Symfony storing cookie headers in HttpCache
Description
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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
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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
https://github.com/symfony/symfony/commit/d2f6322af9444ac5cd1ef3ac6f280dbef7f9d1fb for branch 4.4.
Credits
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We would like to thank Soner Sayakci for reporting the issue and Nicolas Grekas for fixing it.