Wednesday, March 23, 2011

PHP-Nuke 8.x <= Cross Site Request Forgery (CSRF) / Anti-CSRF Bypass Vulnerability

1. OVERVIEW

The PHP-Nuke version 8.x and lower versions are vulnerable to Cross Site Request Forgery (CSRF) because its Anti-CSRF mechanism (Referer Check) is found to be broken.


2. BACKGROUND

PHP-Nuke is a Web Portal System or content management system. The goal of PHP-Nuke is to have an automated web site to distribute news and articles with users system. Each user can submit comments to discuss the articles. Main features include: web based admin, surveys, top page, access stats page with counter, user customizable box, themes manager for registered users, friendly administration GUI with graphic topic manager, option to edit or delete stories, option to delete comments, moderation system, Referrers page to know who link us, sections manager, customizable HTML blocks, user and authors edit, an integrated Banners Ads system, search engine, backend/headlines generation (RSS/RDF format), and many, many more friendly functions. 


3. VULNERABILITY DESCRIPTION

The PHP-Nuke version 8.x and lower versions contain a flaw that allows a remote Cross-site Request Forgery (CSRF / XSRF) attack. The flaw exists because the application does not require multiple steps or explicit confirmation for sensitive transactions for majority of administrator functions such as adding new user, assigning user to administrative privilege. By using a crafted URL, an attacker may trick the victim into visiting to his web page to take advantage of the trust relationship between the authenticated victim and the application. Such an attack could trick the victim into executing arbitrary commands in the context of their session with the application, without further prompting or verification.


4. VERSIONS AFFECTED

8.0 and lower 

Tested version: 8.0
The paid versions, 8.1 and 9.0, of PHP-Nuke may be vulnerable as well.


5. PROOF-OF-CONCEPT/EXPLOIT

Consider the following code snippet in /mainfile.php of PHP-Nuke:

//////////////////////////////////////////////////////////////////////////////

109		if(!function_exists('stripos')) {
			function stripos_clone($haystack, $needle, $offset=0) {
				$return = strpos(strtoupper($haystack), strtoupper($needle), $offset);
				if ($return === false) {
					return false;
				} else {
					return true;
				}
			}
		} else {
			// But when this is PHP5, we use the original function
			function stripos_clone($haystack, $needle, $offset=0) {
				$return = stripos($haystack, $needle, $offset=0);
				if ($return === false) {
					return false;
				} else {
					return true;
				}
			}
128		} 

......

206		// Posting from other servers in not allowed
207		// Fix by Quake
208		// Bug found by PeNdEjO

210		if ($_SERVER['REQUEST_METHOD'] == "POST") {
			if (isset($_SERVER['HTTP_REFERER'])) {
212				if (!stripos_clone($_SERVER['HTTP_REFERER'], $_SERVER['HTTP_HOST'])) {
					die('Posting from another server not allowed!');
				}
			} else {
				die($posttags);
			}
		}
//////////////////////////////////////////////////////////////////////////////

It is clear that stripos_clone checks HTTP_REFERER value whether it matches the target domain or not. 
Attacker can easily bypass it by creating victim domain name under his web root folder like:

http://localhost/victim.com/

From there, he could effectively perform CSRF attacks against php-Nuke users. 

A short P0C demo video can be seen at 
http://yehg.net/lab/pr0js/training/view/misc/PHPNuke_8x_Anti-CSRF-Bypass/


6. SOLUTION

Not Available. 
Use of this product is NOT recommended because of long lack of update and vendor negligence about security reports.


7. VENDOR

PHP-Nuke Developers
http://phpnuke.org/


8. CREDIT

Aung Khant, http://yehg.net, YGN Ethical Hacker Group, Myanmar.


9. DISCLOSURE TIME-LINE

2011-01-01: contacted author through emails
2011-01-25: contacted author through web site contact form
2010-03-23: no replies from author
2010-03-23: vulnerability disclosed


10. REFERENCES

Original Advisory URL: http://yehg.net/lab/pr0js/advisories/[phpnuke-8.x]_cross_site_request_forgery
CSRF Wiki: https://secure.wikimedia.org/wikipedia/en/wiki/Cross-site_request_forgery
About PHP-Nuke: http://en.wikipedia.org/wiki/PHP-Nuke
PHP-Nuke 8.0: http://phpnuke.org/modules.php?name=Downloads&d_op=getit&lid=658
CWE-352: http://cwe.mitre.org/data/definitions/352.html

#yehg [2010-03-23]

keywords: php nuke, php-nuke, phpnuke, 8.0, 8.1, csrf