[MajorSecurity Advisory #38]eXV2 CMS - Session fixation and Cross-Site-Scripting Issues

[Securityaudit () majorsecurity de]

[MajorSecurity Advisory #38]eXV2 CMS - Session fixation and Cross-Site-Scripting Issues

Details
=======
Product: eXV2 CMS <= 2.0.4.3 
Severity: moderated
Remote-Exploit: yes
Vendor-URL: http://www.exv2.com/
Vendor-Status: informed
Advisory-Status: published

Credits
============
Discovered by: David Vieira-Kurz
http://www.majorsecurity.de

Original Advisory:
============
http://www.majorsecurity.de/index_2.php?major_rls=major_rls38

Introduction
============
eXV2 CMS is a Content Management System.

More Details
============
1. Cross Site Scripting:
Input passed directly to the "set_lang" parameter in "archive.php", "article.php", "index.php" and "topics.php" is not 
properly sanitised before being returned to the user.
This can be exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected 
site. 

2. Session fixation:
The Cookie variable "PHPSESSID" can be set to a malicious and arbitrary value.

2.1 Classification:
Session Fixation is an attack technique that forces a user's session ID to an explicit value.
Depending on the functionality of the target web site, a number of techniques can be utilized to "fix" the session ID 
value.
These techniques range from Cross-site Scripting exploits to peppering the web site with previously made HTTP requests.
After a user's session ID has been fixed, the attacker will wait for them to login.
Once the user does so, the attacker uses the predefined session ID value to assume their online identity.

Workaround: [Cross Site Scripting]
=============
Edit the source code to ensure that input is properly sanitised.
You should work with "htmlspecialchars()" or "htmlentities()" php-function to ensure that html tags
are not going to be executed. 

Example:
$pass = htmlentities($_POST['pass']);
$test = htmlspecialchars($_GET('test'));
?>

Workaround: [Session fixation]
============
1. Do not accept session identifiers from GET / POST variables:
Session identifiers in URL (query string, GET variables) or POST variables are not recommended as it simplifies this 
attack - it is easy to make links or forms which sets GET / POST variables.

2.Regenerate SID on each request:
A powerful countermeassure against session fixation is to "regenerate" session identifier (SID) on each request.
This means that although attacker may trick a user into accepting a known SID, the SID will be invalid when attacker 
attempts to re-use the SID.

3. Accept only server generated SID:
One way to improve security is to not accept session identifiers not generated by server.

if ( ! isset( $_SESSION['SERVER_GENERATED_SID'] ) ) {
session_destroy(); // destroy all data in session
}
session_regenerate_id(); // generate a new session identifier
$_SESSION['SERVER_GENERATED_SID'] = true;


History/Timeline
================
01.04.2007 discovery of the vulnerabilities
01.04.2007 additional tests with other versions
02.04.2007 contacted the vendor
02.04.2007 vendor confirmed bugs
04.04.2007 advisory is written
04.04.2007 advisory released

MajorSecurity
=======
MajorSecurity is a German penetration testing and security research project
which consists of only one person at the present time.
http://www.majorsecurity.de/