A security issue and a vulnerability have been reported in MyBB, which can be exploited by malicious users to conduct spoofing and SQL injection attacks.

1) Input passed via avatar extensions is not properly sanitised before being used in SQL queries. This can be exploited to manipulate SQL queries by uploading specially named avatars.

2) The script allows to sign up with usernames containing zero width space characters, which can be exploited to e.g. conduct spoofing attacks.

Note: Additionally, an error within the Custom MyCode implementation can allow administrators to use eval expressions.

Solution
Update to version 1.4.9 or apply patches.
Further details available to Secunia VIM customers

Provided and/or discovered by
The vendor credits endeavormac, frostschutz, and TheLinx.

Original Advisory
http://blog.mybboard.net/2009/09/21/mybb-1-4-9-released-security-update/

1) http://dev.mybboard.net/issues/464
2) http://dev.mybboard.net/issues/418

http://dev.mybboard.net/issues/317

Deep Links
Links available to Secunia VIM customers