An issue was discovered in Squid 3.3.9 through 3.5.28 and 4.x through 4.7. When Squid is configured to use Digest authentication, it parses the header Proxy-Authorization. It searches for certain tokens such as domain, uri, and qop. Squid checks if this token's value starts with a quote and ends with one. If so, it performs a memcpy of its length minus 2. Squid never checks whether the value is just a single quote (which would satisfy its requirements), leading to a memcpy of its length minus 1.
https://www.debian.org/security/2019/dsa-4507
https://usn.ubuntu.com/4065-2/
https://usn.ubuntu.com/4065-1/
https://seclists.org/bugtraq/2019/Aug/42
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html
https://lists.debian.org/debian-lts-announce/2019/07/msg00018.html
https://github.com/squid-cache/squid/commits/v4
http://www.squid-cache.org/Versions/v4/changesets/
http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00056.html
http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00053.html