[MajorSecurity Advisory #40]onelook oboShop - Session fixation Issue

Details

Product: oboShop
Remote-Exploit: yes
Vendor-URL: http://www.onebyone.ch/
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_rls40

Introduction

oboShop is a E-Commerce WebShop Script.

More Details

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

1.1 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:

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;

References:

http://www.acrossecurity.com/papers/session_fixation.pdf
http://www.webappsec.org/projects/threat/classes/session_fixation.shtml

History/Timeline

29.03.2007 discovery of the vulnerability
30.03.2007 additional tests with other versions
03.04.2007 contacted the vendor
05.04.2007 advisory is written
06.04.2007 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/