An issue was discovered in Squid 3.x and 4.x through 4.8 when the append_domain setting is used (because the appended characters do not properly interact with hostname length restrictions). Due to incorrect message processing, it can inappropriately redirect traffic to origins it should not be delivered to.
www.squid-cache.org/Advisories/SQUID-2019_9.txt
www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-e5f1813a674848dde570f7920873e1071f96e0b4.patch
www.squid-cache.org/Versions/v4/changesets/squid-4-36492033ea4097821a4f7ff3ddcb971fbd1e8ba0.patch
bugzilla.suse.com/show_bug.cgi?id=1156328
github.com/squid-cache/squid/pull/427
lists.debian.org/debian-lts-announce/2019/12/msg00011.html
lists.debian.org/debian-lts-announce/2020/07/msg00009.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MTM74TU2BSLT5B3H4F3UDW53672NVLMC/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UEMOYTMCCFWK5NOXSXEIH5D2VGWVXR67/
usn.ubuntu.com/4213-1/
www.debian.org/security/2020/dsa-4682