source: http://www.securityfocus.com/bid/34798/info

MyBB is prone to multiple security vulnerabilities, including an HTML-injection issue and an unspecified issue.

An attacker may leverage the HTML-injection issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may allow the attacker to steal cookie-based authentication credentials, control how the site is rendered to the user, and to launch other attacks.

MyBB 1.4.5 is vulnerable; other versions may also be affected.

http://www.example.com/somefile.png?"><script>alert('xss')</script>