Squid Internet Object Cache 1.1.20 allows users to bypass access control lists (ACLs) by encoding the URL with hexadecimal escape sequences.
Squid 2.2.STABLE5 and below, when using external authentication, allows attackers to bypass access controls via a newline in the user/password pair.
squid 2.3 and earlier allows local users to overwrite arbitrary files via a symlink attack in some configurations.