source: https://www.securityfocus.com/bid/9919/info

Reportedly SquidGuard is prone to a remote NULL URL character unauthorized access vulnerability. This issue is due to a failure of the application to properly filter out invalid URIs.

Successful exploitation of this issue may allow a remote attacker to bypass access controls resulting in unauthorized access to attacker-specified resources. This may allow the attacker to gain unauthorized access to sensitive resources.

http://foo%00@www.example.com/