BroScience HackTheBox Writeup
Scanning
We launch nmap tool with scripts and versions on all ports.
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 8.4p1 Debian 5+deb11u1 (protocol 2.0)
| ssh-hostkey:
| 3072 df17c6bab18222d91db5ebff5d3d2cb7 (RSA)
| 256 3f8a56f8958faeafe3ae7eb880f679d2 (ECDSA)
|_ 256 3c6575274ae2ef9391374cfdd9d46341 (ED25519)
80/tcp open http Apache httpd 2.4.54
|_http-server-header: Apache/2.4.54 (Debian)
|_http-title: Did not follow redirect to https://broscience.htb/
443/tcp open ssl/http Apache httpd 2.4.54 ((Debian))
| http-cookie-flags:
| /:
| PHPSESSID:
|_ httponly flag not set
| ssl-cert: Subject: commonName=broscience.htb/organizationName=BroScience/countryName=AT
| Not valid before: 2022-07-14T19:48:36
|_Not valid after: 2023-07-14T19:48:36
|_http-title: BroScience : Home
| tls-alpn:
|_ http/1.1
|_ssl-date: TLS randomness does not represent time
|_http-server-header: Apache/2.4.54 (Debian)
Service Info: Host: broscience.htb; OS: Linux; CPE: cpe:/o:linux:linux_kernel
We see that nmap shows us the domain broscience.htb, so we include it in our /etc/hosts file.
Enumeration
Web access the website:
We detected a couple of interesting parameters, and we also listed the users on the site.
We managed to list all the users on the platform by changing the identifier.
In addition, there is an authentication and registration form, but the registration is not enabled.
We created a Python script for brute-forcing and managed to enumerate the credentials of the user ‘hacker’, but the account is not activated.
Exploitation
After trying to use the activate.php file and being unable to determine the code, we discovered that some variables load the ID or other functionalities. As a result, we tested the img.php file.
We tried with the ‘path’ parameter, and it seems to attempt to load the file, but without success.
We attempted a basic Local File Inclusion attack and noticed that the code mitigates the attack through some filtering mechanism. However, this is interesting because the vulnerability is likely to be located here.
We used the payloads from HackTricks and found that we were able to bypass the protection with the first few attempts.
It seems that we don’t need to use any wrappers, so we can read the contents of the PHP files.
We are viewing the register.php file:
We are enumerating the utils.php file, which is responsible for generating the random activation code. We can generate the activation code ourselves, so we will download the code to obtain the activation code.
Now that we have the code, we can create a small script that generates valid tokens associated with the registration date and time in a loop, and activate it ourselves without being an administrator.
Proof of concept
Using the exploit to generate one token per second:
To simplify the process, I used all the tokens and launched it with the Intruder tool in Burp Suite to filter by the response ‘Account activated!’
We authenticate ourselves and access the user panel:
After reviewing all the PHP files, it seems that this one writes content in temporary files of the path of an image:
<?php
class Avatar {
public $imgPath;
public function __construct($imgPath) {
$this->imgPath = $imgPath;
}
public function save($tmp) {
$f = fopen($this->imgPath, "w");
fwrite($f, file_get_contents($tmp));
fclose($f);
}
}
class AvatarInterface {
public $tmp;
public $imgPath;
public function __wakeup() {
$a = new Avatar($this->imgPath);
$a->save($this->tmp);
}
}
$code = base64_encode(serialize(new AvatarInterface));
echo "$code"
?>
We did a test and found that we can serialize and deserialize the ‘code’ parameter correctly.
We generated our malicious payload to obtain a reverse shell.
We copied the payload and placed it in the cookie, then reloaded the website.
In my scenario, I set up a server with Python to run my ‘m3.php’ file on the victim server. This file contains a classic reverse shell from Pentester Monkey:
We waited for the server to execute the payload, and then we obtained an interactive connection with the victim machine.
Once inside, I enumerated the database and extracted the hashes it stored, and then attempted to crack them with hashcat.
Cracking with hashcat
We reused Bill’s credentials to authenticate via SSH.
Privilege Escalation
It seems that there’s a bash script for renewing certificates, and they’re being moved to Bill’s folder.
We launched the pspy tool and observed the execution of the script:
We created the certificate and injected a reverse shell into several fields, with the idea of it being executed by the root user and obtaining privileged shell access.
