source: https://www.securityfocus.com/bid/53413/info

JibberBook is prone to a security-bypass vulnerability that may allow attackers to perform actions without proper authorization.

Attackers can exploit this issue to bypass authentication to gain administrative privileges ; this may aid in launching further attacks.

JibberBook 2.3 is vulnerable; other versions may also be affected. 

http://www.example.com/Admin/Login_form.php?loggedin=true