Symfony storing cookie headers in HttpCache

Description

The Symfony HTTP cache system acts as a reverse proxy: it caches HTTP responses (including headers) and returns them to clients.

In a recent AbstractSessionListener change, the response might now contain a Set-Cookie header. If the Symfony HTTP cache system is enabled, this header might be stored and returned to some other clients. An attacker can use this vulnerability to retrieve the victim’s session.

Resolution

The HttpStore constructor now takes a parameter containing a list of private headers that are removed from the HTTP response headers.
The default value for this parameter is Set-Cookie, but it can be overridden or extended by the application.

The patch for this issue is available here for branch 4.4.

Credits

We would like to thank Soner Sayakci for reporting the issue and Nicolas Grekas for fixing it.