[MajorSecurity Advisory #47]Simple Machines Forum (SMF) - Session fixation Issue Details ======= Product: Simple Machines Forum (SMF) Affected version: 1.1.2 and prior Remote-Exploit: yes Vendor-URL: http://www.simplemachines.org 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_rls47 Introduction ============ "Simple Machines Forum ? SMF in short ? is a free, professional grade software package that allows you to set up your own online community within minutes." -from simplemachines.org More Details ============ 1. Session fixation: The "PHPSESSID" parameter can be set to a malicious and arbitrary value. 1.1 Description: In a session fixation attack, the attacker fixes the user's session ID before the user even logs into the target server. 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. 2.Regenerate SID on each request. 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 ================ 30.04.2007 discovery of the vulnerability 03.04.2007 contacted the vendor 04.04.2007 working patch sent to the vendor 05.04.2007 advisory is written 05.04.2007 advisory released MajorSecurity ======= MajorSecurity is a non-profit German penetration testing and security research project which consists of only one person at the present time. http://www.majorsecurity.de/