{"id":"CVE-2021-41267","aliases":["BIT-symfony-2021-41267","GHSA-q3j3-w37x-hq2q"],"url":"https://o3.security/vulnerability/CVE-2021-41267","summary":"Webcache Poisoning in symfony/http-kernel","details":"Symfony/Http-Kernel is the HTTP kernel component for Symfony, a PHP framework for web and console applications and a set of reusable PHP components. Headers that are not part of the \"trusted_headers\" allowed list are ignored and protect users from \"Cache poisoning\" attacks. In Symfony 5.2, maintainers added support for the `X-Forwarded-Prefix` headers, but this header was accessible in SubRequest, even if it was not part of the \"trusted_headers\" allowed list. An attacker could leverage this opportunity to forge requests containing a `X-Forwarded-Prefix` header, leading to a web cache poisoning issue. Versions 5.3.12 and later have a patch to ensure that the `X-Forwarded-Prefix` header is not forwarded to subrequests when it is not trusted.","published":"2021-11-24T19:15:07.737Z","modified":"2026-08-07T19:57:38.075293Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"symfony/http-kernel","fixedVersion":"5.3.12"},{"ecosystem":"Packagist","name":"symfony/symfony","fixedVersion":"5.3.12"}],"fix":{"url":"https://github.com/symfony/symfony/commit/95dcf51682029e89450aee86267e3d553aa7c487","label":"symfony/symfony@95dcf51"},"references":[{"type":"ADVISORY","url":"https://github.com/symfony/symfony/releases/tag/v5.3.12"},{"type":"FIX","url":"https://github.com/symfony/symfony/commit/95dcf51682029e89450aee86267e3d553aa7c487"},{"type":"FIX","url":"https://github.com/symfony/symfony/pull/44243"},{"type":"FIX","url":"https://github.com/symfony/symfony/security/advisories/GHSA-q3j3-w37x-hq2q"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T19:57:38.075293Z"}}