Webcache Poisoning in Symfony

Vulnerability 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.

References

• https://github.com/symfony/symfony/pull/44243
• https://github.com/symfony/symfony/releases/tag/v5.3.12
• https://github.com/symfony/symfony/security/advisories/GHSA-q3j3-w37x-hq2q
• https://github.com/symfony/symfony/commit/95dcf51682029e89450aee86267e3d553aa7c487