Cross-site scripting (XSS) vulnerability in Sources/Register.php in Simple Machine Forum (SMF) 1.0.6 allows remote attackers to inject arbitrary web script or HTML via the X-Forwarded-For HTTP header field.

Simple Machines Forum (SMF) 1-0-5 and earlier supports the use of URLs for avatar images, which allows remote attackers to monitor sensitive information of forum visitors such as IP address and user agent, as demonstrated using a PHP script on a malicious server.