[HackTheBox] Lame

Lame Card

Summary

  • Nmap reveals that VSFTPD and Samba services are running.
  • VSFTPD's popular exploit doesn't work.
  • SMB's 'Username' map script' Command Execution exploit on version 3.0.20 works perfectly and instantly gives a shell as root.

Recon

Port Scan

nmap -n -sV -p- -T 5 -Pn 10.10.10.3

PORT     STATE SERVICE     VERSION
21/tcp   open  ftp         vsftpd 2.3.4
22/tcp   open  ssh         OpenSSH 4.7p1 Debian 8ubuntu1 (protocol 2.0)
139/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
3632/tcp open  distccd     distccd v1 ((GNU) 4.2.4 (Ubuntu 4.2.4-1ubuntu4))
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

FTP

nmap -n -A -p 21 -T 5 -Pn 10.10.10.3

PORT   STATE SERVICE VERSION
21/tcp open  ftp     vsftpd 2.3.4
|_ftp-anon: Anonymous FTP login allowed (FTP code 230)
| ftp-syst: 
|   STAT: 
| FTP server status:
|      Logged in as ftp
|      TYPE: ASCII
|      No session bandwidth limit
|      Session timeout in seconds is 300
|      Control connection is plain text
|      Data connections will be plain text
|      vsFTPd 2.3.4 - secure, fast, stable
|_End of status
Service Info: OS: Unix

Exploit

There is a popular exploit for this version of VSFTPD (2.3.4) that I've seen in many CTF's before. It utilizes a malicious backdoor that was added to the VSFTPD download archive. The exploit I've used is available HERE.

Surprisingly... it didn't work.

SMB

nmap -A -T 5 -n -p 139,445 -Pn 10.10.10.3

PORT     STATE SERVICE     VERSION
139/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 3.0.20-Debian (workgroup: WORKGROUP)
Host script results:
|_clock-skew: mean: -3d00h52m19s, deviation: 2h49m42s, median: -3d02h52m19s
| smb-os-discovery: 
|   OS: Unix (Samba 3.0.20-Debian)
|   Computer name: lame
|   NetBIOS computer name: 
|   Domain name: hackthebox.gr
|   FQDN: lame.hackthebox.gr
|_  System time: 2020-07-04T10:20:51-04:00
| smb-security-mode: 
|   account_used: <blank>
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
|_smb2-time: Protocol negotiation failed (SMB2)

Exploit

A quick search on ExploitDB revealed an exploit for this exact version (3.0.20) of Samba.

"This module exploits a command execution vulnerability in Samba versions 3.0.20 through 3.0.25rc3 when using the non-default "username map script" configuration option. By specifying a username containing shell meta characters, attackers can execute arbitrary commands. No authentication is needed to exploit this vulnerability since this option is used to map usernames prior to authentication!"
~Rapid7

It is available HERE.

After setting up module and payload options in Metasploit we get an instant root shell!

Lame Shell