[MajorSecurity Advisory #41]onelook courts online - Session fixation Issue Apr 06 2007 07:43AM
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[MajorSecurity Advisory #41]onelook courts online - Session fixation Issue

Product: courts online
Remote-Exploit: yes
Vendor-URL: http://www.onebyone.ch/
Vendor-Status: informed
Advisory-Status: published

Discovered by: David Vieira-Kurz

Original Advisory:

courts online is an Online Booking 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.

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


29.03.2007 discovery of the vulnerability
30.03.2007 additional tests with other versions
03.04.2007 contacted the vendor
03.04.2007 advisory is written
04.04.2007 advisory released

MajorSecurity is a German penetration testing and security research project
which consists of only one person at the present time.

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