RCE in 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 for the 4.4 branch.

Credits

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