An updated squid package is avaliable that fixes a security vulnerability in URL decoding and provides a new ACL type for protecting vulnerable clients.
Squid is a full-featured Web proxy cache. A bug was found in the processing of %-encoded characters in a URL in versions of Squid 2.5.STABLE4 and earlier. If a Squid configuration uses Access Control Lists (ACLs), a remote attacker could create URLs that would not be correctly tested against Squid's ACLs, potentially allowing clients to access prohibited URLs. Users of Squid should update to these erratum packages which are not vulnerable to this issue. In addition, these packages contain a new Access Control type, "urllogin", which can be used to protect vulnerable Microsoft Internet Explorer clients from accessing URLs that contain login information. Such URLs are often used by fraudsters to trick web users into revealing valuable personal data. Note that the default Squid configuration does not make use of this new access control type. You must explicitly configure Squid with ACLs that use this new type, in accordance with your own site policies.