Squid before 2.3STABLE5 in HTTP accelerator mode does not enable access control lists (ACLs) when the httpd_accel_host and http_accel_with_proxy off settings are used, which allows attackers to bypass the ACLs and conduct unauthorized activities such as port scanning.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6862
http://www.securityfocus.com/archive/1/197727
http://www.redhat.com/support/errata/RHSA-2001-097.html
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-066.php3
http://www.calderasystems.com/support/security/advisories/CSSA-2001-029.0.txt
http://download.immunix.org/ImmunixOS/7.0/updates/IMNX-2001-70-031-01
http://archives.neohapsis.com/archives/bugtraq/2001-07/0362.html