Affected versions
Symfony 4.3, 4.4.0 to 4.4.12, 5.0, and 5.1.0 to 5.1.4 versions of the Symfony HttpClient component are affected by this security issue.
The issue has been fixed in Symfony 4.4.13 and 5.1.5. Symfony 4.3 and 5.0 won't be patched as they are not maintained anymore.
Description
The CachingHttpClient class from the HttpClient Symfony componeny 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.