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

Panoptic
An overview of Panoptic, an open source penetration testing tool that automates the process of search and retrieval of common log and config files through LFI vulnerabilities.

Special discount code for "Nmap 6: Network Exploration and Security Auditing Cookbook"
PacktPub created a special discount code for our friends from HackerHalted

Mac2WepKey HHG5xx for iPhone
The famous app to obtain the default WiFi passwords for Huawei routers is now available for the iPhone iOS 5.

Latest News

Oct 01, 2013
Websec at DerbyCon 2013
A summary of Websec's participation at DerbyCon 2013 in Louisville, Kentucky.

Sep 16, 2013
Websec's participation at Black Hat, CSI and XCon
Websec is grateful to have been able to participate in the month of August at great conferences such as Black Hat, CSI and XCon.