{"id":"CVE-2021-41267","aliases":["BIT-symfony-2021-41267","EUVD-2021-2377","GHSA-q3j3-w37x-hq2q"],"status":"published","title":"Webcache Poisoning in Symfony","description":"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.","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.0128,"percentile":0.70214,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-444"],"published":"2021-11-24T18:55:17Z","modified":"2026-10-24T10:50:42Z","fixes":[{"ecosystem":"Packagist","package":"symfony/http-kernel","fixed_in":["5.3.12"],"sources":["ghsa","osv"]},{"ecosystem":"Packagist","package":"symfony/symfony","fixed_in":["5.3.12"],"sources":["ghsa","osv"]},{"ecosystem":"Bitnami","package":"symfony","fixed_in":["5.3.12"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Packagist","package":"symfony/http-kernel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.2.0"},{"fixed":"5.3.12"}]}]},{"source":"ghsa","ecosystem":"Packagist","package":"symfony/symfony","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.2.0"},{"fixed":"5.3.12"}]}]},{"source":"osv","ecosystem":"Bitnami","package":"symfony","ranges":[{"type":"SEMVER","events":[{"introduced":"5.2.0"},{"fixed":"5.3.12"}]}]},{"source":"osv","ecosystem":"Packagist","package":"symfony/http-kernel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.2.0"},{"fixed":"5.3.12"}]}],"versions":["v5.2.0","v5.2.1","v5.2.10","v5.2.11","v5.2.12","v5.2.13","v5.2.14","v5.2.2","v5.2.3","v5.2.4","v5.2.5","v5.2.6","v5.2.7","v5.2.8","v5.2.9","v5.3.0","v5.3.0-BETA1","v5.3.0-BETA2","v5.3.0-BETA3","v5.3.0-BETA4","v5.3.0-RC1","v5.3.1","v5.3.10","v5.3.11","v5.3.2","v5.3.3","v5.3.4","v5.3.5","v5.3.6","v5.3.7","v5.3.8","v5.3.9"]},{"source":"osv","ecosystem":"Packagist","package":"symfony/symfony","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.2.0"},{"fixed":"5.3.12"}]}],"versions":["v5.2.0","v5.2.1","v5.2.10","v5.2.11","v5.2.12","v5.2.13","v5.2.14","v5.2.2","v5.2.3","v5.2.4","v5.2.5","v5.2.6","v5.2.7","v5.2.8","v5.2.9","v5.3.0","v5.3.0-BETA1","v5.3.0-BETA2","v5.3.0-BETA3","v5.3.0-BETA4","v5.3.0-RC1","v5.3.1","v5.3.10","v5.3.11","v5.3.2","v5.3.3","v5.3.4","v5.3.5","v5.3.6","v5.3.7","v5.3.8","v5.3.9"]}],"products":[{"vendor":"sensiolabs","product":"symfony"},{"vendor":"symfony","product":"symfony"}],"references":[{"url":"https://github.com/symfony/symfony/pull/44243","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","web","fix"]},{"url":"https://github.com/symfony/symfony/releases/tag/v5.3.12","tags":["x_refsource_MISC","x_transferred","Release Notes","Third Party Advisory","web","advisory"]},{"url":"https://github.com/symfony/symfony/security/advisories/GHSA-q3j3-w37x-hq2q","tags":["x_refsource_CONFIRM","x_transferred","Patch","Third Party Advisory","web","fix"]},{"url":"https://github.com/symfony/symfony/commit/95dcf51682029e89450aee86267e3d553aa7c487","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","web","fix"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-41267","tags":["advisory"]},{"url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/http-kernel/CVE-2021-41267.yaml","tags":["web"]},{"url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2021-41267.yaml","tags":["web"]},{"url":"https://symfony.com/cve-2021-41267","tags":["web"]},{"url":"https://github.com/advisories/GHSA-q3j3-w37x-hq2q"}],"sources":{"cve":[{"id":"CVE-2021-41267","title":"Webcache Poisoning in Symfony","description":"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.","status":"published","published":"2021-11-24T18:55:17Z","modified":"2024-08-04T03:08:31.656Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-444"],"updated_at":"2026-11-02T14:32:59.105382Z"}],"euvd":[{"id":"EUVD-2021-2377","description":"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.","status":"published","published":"2021-11-24T18:55:17Z","modified":"2024-08-04T03:08:31Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-03T03:24:18.226903Z"}],"ghsa":[{"id":"GHSA-q3j3-w37x-hq2q","title":"Webcache Poisoning in symfony/http-kernel","description":"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","status":"published","published":"2021-11-24T20:04:25Z","modified":"2024-02-05T11:13:50Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-444"],"updated_at":"2026-11-02T14:37:35.293818Z"}],"nvd":[{"id":"CVE-2021-41267","description":"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.","status":"published","published":"2021-11-24T19:15:07.737Z","modified":"2026-06-17T04:08:12.26Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium","assessor":"secondary"},{"version":"2.0","score":4.3,"vector":"AV:N/AC:M/Au:N/C:N/I:P/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-444"],"updated_at":"2026-11-02T14:07:01.428028Z"}],"osv":[{"id":"CVE-2021-41267","description":"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.","status":"published","published":"2021-11-24T19:15:07.737Z","modified":"2026-10-24T10:50:42.85284915Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T15:44:21.557945Z"},{"id":"GHSA-q3j3-w37x-hq2q","title":"Webcache Poisoning in symfony/http-kernel","description":"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","status":"published","published":"2021-11-24T20:04:25Z","modified":"2026-07-08T06:28:30.044634543Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-444"],"updated_at":"2026-11-02T15:46:54.055966Z"},{"id":"BIT-symfony-2021-41267","description":"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.","status":"published","published":"2024-03-06T11:07:55.104Z","modified":"2024-03-06T11:25:28.861Z","updated_at":"2026-11-02T15:28:35.51001Z"}]}}