MyBB contains a flaw that may allow an attacker to carry out an SQL injection attack. The issue is due to the inc/function_upload.php script not properly sanitizing user-supplied input to the file extension of the uploaded file. This may allow an attacker to inject or manipulate SQL queries in the back-end database.
Upgrade to version 1.0.2 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.