Vulnerability in Squid before 2.4.STABLE6 related to proxy authentication credentials may allow remote web sites to obtain the user's proxy login and password.
http://www.squid-cache.org/Versions/v2/2.4/bugs/
http://www.squid-cache.org/Advisories/SQUID-2002_3.txt
http://www.securityfocus.com/bid/5154
http://www.linux-mandrake.com/en/security/2002/MDKSA-2002-044.php
http://www.iss.net/security_center/static/9478.php
http://rhn.redhat.com/errata/RHSA-2002-130.html