Anti-CSRF Filter Bypass SMF 2.0 / 1.1.14

Anti-CSRF Filter Bypass SMF 2.0 / 1.1.14

Posted on Aug 23 2011   |  Plain text version

Summary

The [img] BBCode tag anti-CSRF filter can be bypassed due to incorrect parsing of the 'action' variable, because of this it is possible to execute CSRF successfully.

Description

Software: Simple Machines Forum (SMF)
Versions: SMF 1.1.14 - 2.0
Publication date: 2011-08-23
Impact: Cross Site Request Forgery
Solution: N/A (Vendor informed)
Websec-id: ws11-15

When a user posts a URL as the source of an [img] tag and it seems malicious, SMF tries to avoid execution of the action parameter by replacing the string "action=something" with "action-something".

If a user makes a specially crafted URL by adding to the end of the variable name a null-byte (%00), the filter is successfully circumvented and CSRF can be achieved.

POC

Remove user 102 from the buddy list (SMF 1.1.14):
[img]http://example.com/index.php?sa=editBuddies;remove=102;action%00=profile[/img]

Logout (SMF 2.0):
[img]http://example.com/community/index.php?action%00=logout;token[/img]

Christian Yerena
cyerena [ at ] websec [ dot ] mx


Latest Blog Entries

Downloading an Application's Entire Source Code Through an Exposed GIT Directory
Website administrators sometimes inadvertently leave an exposed .git directory, from which it is possible to download the entire source code of the web application using just wget and a common server misconfiguration.

credmap: The Credential Mapper
An overview of credmap, an open source penetration testing tool that automates the process of testing for credential reuse. It does so by testing supplied user credentials on known websites and verifies if the password has been reused on any of these.

New publication: Mastering the Nmap Scripting Engine
We invite you to learn more about the latest publication from our team, "Mastering the Nmap Scripting Engine".

Latest News

Blackhat EU 2015
Websec participated with two tools at the Blackhat, EU Arsenal held in Amsterdam, NL from the 10-13 of November, 2015. During this event, we introduced our brand new tool "credmap: The Credential Mapper" and also presented an amped-up version of Panoptic.

BSides Vancouver 2015
Websec is proud to announce that we will be attending the 3rd annual edition of BSides Vancouver, a local non-profit information security conference held in the heart of Vancouver, BC on March 16 and 17.