Cross-site scripting (XSS) vulnerability in index.php in Simple Machines Forum (SMF) allows remote attackers to inject arbitrary web script or HTML via a base64 encoded params value in the action parameter.

DISPUTED NOTE: this issue has been disputed by the vendor and third parties. SQL injection vulnerability in Memberlist.php in Simple Machines Forum (SMF) 1.1 rc1 and earlier allows remote attackers to execute arbitrary SQL commands via the start parameter. NOTE: the vendor says that since only one character can be modified, there is no SQL injection. Thus this might be an "invalid SQL syntax error." Multiple followups support the vendor.