Gunhead was the second web hacking challenge of the Hack The Box Cyber Apocalypse Capture The Flag competition. Hello world, welcome to Haxez where I will be talking about the web hacking challenge Gunhead. Notably, this challenge is a great step up from the first challenge and like the other challenges here is the description.
During Pandora’s training, the Gunhead AI combat robot had been tampered with and was now malfunctioning, causing it to become uncontrollable. With the situation escalating rapidly, Pandora used her hacking skills to infiltrate the managing system of Gunhead and urgently needs to take it down.
Enumerating The Gunhead Application
The Gunhead application had a bit more functionality than the first application. It appeared to be an interface for a weapons control system. There were a number of interactable icons on the right side of the page. The first option showed us the status of the bot, the second told us its needs and the third appeared to be a command window.
The command window had a help option. Obviously, running ‘/HELP’ in the terminal showed us that we had a number of commands that we could run. These commands included ‘/CLEAR’ to clear the current terminal, ‘/STORAGE’ to list the current storage space and ‘/PING’ which lets us ping a target.
Looking at the source it seems that ‘/STORAGE’ command is printing prewritten information. However, the ‘/PING’ command appears to be directly invoking systems commands. If we can find a way to tack on additional commands then perhaps we can enumerate the filesystem and find and cat the flag.
Gunhead Command Injection
By running the ping command with an IP address and a semicolon, we can add our own commands on to the end such as the list command. For example, if we were to run ‘/PING 10.10.10.10; LS -LASH;’ then we would see the output of the list command. Unfortunately no ‘flag.txt’ file here.
If we continue enumerating the filesystem we can see that the flag file is in the ‘/’ directory. Consequently, all we should need to do now is cat the file.
Gunhead Capture The Flag
As shown below, we were able to capture the flag.txt file by appending the ‘cat’ command. Next, all we need to do now is copy the flag and submit and we’re done.
The Gunhead web hacking challenge was a lot of fun and a good place to start learning about command injection. I remember that the Mr Robot lab had a similar vulnerability. Anyway, there isn’t much more to say about the challenge than that. It was well-designed and had fun visuals. I like challenges with strong themes as it helps to immerse you.