source: https://www.securityfocus.com/bid/17537/info

phpGuestbook is prone to an HTML-injection vulnerability because the application fails to properly sanitize user-supplied input before using it in dynamically generated content. 

Attacker-supplied HTML and script code would be executed in the context of the affected website, potentially allowing an attacker to steal cookie-based authentication credentials. An attacker could also exploit this issue to control how the site is rendered to the user; other attacks are also possible. 

Versions 1.0 and prior are vulnerable.

Post Comment:-

Name: '><script>alert(document.cookie)</script>
Website:
Comment: '><script>alert(document.cookie)</script>