An issue was discovered in Squid through 4.13 and 5.x through 5.0.4. Due to improper input validation, it allows a trusted client to perform HTTP Request Smuggling and access services otherwise forbidden by the security controls. This occurs for certain uri_whitespace configuration settings.
https://www.debian.org/security/2021/dsa-4873
https://security.netapp.com/advisory/ntap-20210727-0010/
https://security.gentoo.org/glsa/202105-14
https://github.com/squid-cache/squid/security/advisories/GHSA-jvf6-h9gj-pmj6
http://www.squid-cache.org/Versions/v5/changesets/SQUID-2020_11.patch
http://www.squid-cache.org/Versions/v4/changesets/SQUID-2020_11.patch