Squid is a high-performance proxy caching server for web clients, supporting FTP, Gopher, and HTTP data objects. A flaw was found in the way Squid processed certain external ACL helper HTTP header fields that contained a delimiter that was not a comma. A remote attacker could issue a crafted request to the Squid server, causing excessive CPU use . Note: The CVE-2009-2855 issue only affected non-default configurations that use an external ACL helper script. A flaw was found in the way Squid handled truncated DNS replies. A remote attacker able to send specially-crafted UDP packets to Squid"s DNS client port could trigger an assertion failure in Squid"s child process, causing that child process to exit. This update also fixes the following bugs: * Squid"s init script returns a non-zero value when trying to stop a stopped service. This is not LSB compliant and can generate difficulties in cluster environments. This update makes stopping LSB compliant. * Squid is not currently built to support MAC address filtering in ACLs. This update includes support for MAC address filtering. * Squid is not currently built to support Kerberos negotiate authentication. This update enables Kerberos authentication. * Squid does not include the port number as part of URIs it constructs when configured as an accelerator. This results in a 403 error. This update corrects this behavior. * the error_map feature does not work if the same handling is set also on the HTTP server that operates in deflate mode. This update fixes this issue. All users of squid should upgrade to this updated package, which resolves these issues. After installing this update, the squid service will be restarted automatically.