DRBGuestbook "action" Cross-Site Scripting Vulnerability

Gokhan has discovered a vulnerability in DRBGuestbook, which can be exploited by malicious people to conduct cross-site scripting attacks.

Input passed to the "action" parameter in index.php is not properly sanitised before being returned to the user. This can be exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected site.

The vulnerability is confirmed in version 1.1.13. Prior versions may also be affected.