This script is Copyright (C) 2009-2015 Tenable Network Security, Inc.
The remote FreeBSD host is missing a security-related update.
From the Squid advisory :
Squid versions 2.5.STABLE4 and earlier contain a bug in the '%xx' URL
decoding function. It may insert a NUL character into decoded URLs,
which may allow users to bypass url_regex ACLs.
See also :
Update the affected package.
Risk factor :
High / CVSS Base Score : 7.5