{"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":"Description\n-----------\n\nWhen a Symfony application is running behind a proxy or a load-balancer, you can tell Symfony to look for the `X-Forwarded-*` HTTP headers. HTTP headers that are not part of the \"trusted_headers\" allowed list are ignored and protect you from \"Cache poisoning\" attacks. \n\nIn Symfony 5.2, we've added support for the `X-Forwarded-Prefix` header, but this header was accessible in sub-requests, 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` HTTP header, leading to a web cache poisoning issue.\n\nResolution\n----------\n\nSymfony now ensures that the `X-Forwarded-Prefix` HTTP header is not forwarded to sub-requests when it is not trusted.\n\nThe patch for this issue is available [here](https://github.com/symfony/symfony/commit/95dcf51682029e89450aee86267e3d553aa7c487) for branch 5.3.\n\nCredits\n-------\n\nWe would like to thank Soner Sayakci for reporting the issue and Jérémy Derussé for fixing the issue.\n","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":{"score":0.0128,"percentile":0.68592,"asOf":"2026-09-17"},"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"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-41267"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/http-kernel/CVE-2021-41267.yaml"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2021-41267.yaml"},{"type":"WEB","url":"https://symfony.com/cve-2021-41267"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T19:57:38.075293Z"}}