In Symfony before versions 4.4.13 and 5.1.5, the CachingHttpClient class from the HttpClient Symfony component relies on the HttpCache class to handle requests. HttpCache uses internal headers like X-Body-Eval and X-Body-File to control the restoration of cached responses. The class was initially written with surrogate caching and ESI support in mind (all HTTP calls come from a trusted backend in that scenario). But when used by CachingHttpClient and if an attacker can control the response for a request being made by the CachingHttpClient, remote code execution is possible. This has been fixed in versions 4.4.13 and 5.1.5.

Affected: Packagist: symfony/http-kernel, Packagist: symfony/symfony

Description -----------

The `CachingHttpClient` class from the HttpClient Symfony component relies on the `HttpCache` class to handle requests. `HttpCache` uses internal headers like `X-Body-Eval` and `X-Body-File` to control the restoration of cached responses. The class was initially written with surrogate caching and ESI support in mind (all HTTP calls come from a trusted backend in that scenario). But when used by `CachingHttpClient` and if an attacker can control the response for a request being made by the `CachingHttpClient`, remote code execution is possible.

Resolution ----------

HTTP headers designed for internal use in `HttpCache` are now stripped from remote responses before being passed to `HttpCache`.

The patch for this issue is available [here](https://github.com/symfony/symfony/commit/d9910e0b33a2e0f993abff41c6fbc86951b66d78) for the 4.4 branch.

Credits -------

I would like to thank Matthias Pigulla (webfactory GmbH) for reporting and fixing the issue.