In PHP versions 7.2.x below 7.2.34, 7.3.x below 7.3.23 and 7.4.x below 7.4.11, when PHP is processing incoming HTTP cookie values, the cookie names are url-decoded. This may lead to cookies with prefixes like __Host confused with cookies that decode to such prefix, thus leading to an attacker being able to forge cookie which is supposed to be secure. See also CVE-2020-8184 for more information.
https://www.tenable.com/security/tns-2021-14
https://www.oracle.com/security-alerts/cpuoct2021.html
https://www.debian.org/security/2021/dsa-4856
https://usn.ubuntu.com/4583-1/
https://security.netapp.com/advisory/ntap-20201016-0001/
https://security.gentoo.org/glsa/202012-16
https://lists.debian.org/debian-lts-announce/2020/10/msg00008.html
https://hackerone.com/reports/895727
https://bugs.php.net/bug.php?id=79699
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00067.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00045.html