Description

When a Response does not contain a Content-Type header, Symfony falls back to the format defined in the Accept header of the request, leading to a possible mismatch between the response's content and Content-Type header. When the response is cached, this can lead to a corrupted cache where the cached format is not the right one.

Resolution

Symfony does not use the Accept header anymore to guess the Content-Type.

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

Credits

I would like to thank Xavier Lacot from JoliCode for reporting & Yonel Ceruto and Tobias Schultze for fixing the issue.

References

• GHSA-mcx4-f5f5-4859
• symfony/symfony@dca3434
• https://nvd.nist.gov/vuln/detail/CVE-2020-5255
• https://symfony.com/blog/cve-2020-5255-prevent-cache-poisoning-via-a-response-content-type-header
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/C36JLPHUPKDFAX6D5WYFC4ALO2K7RDUQ/
• https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/http-foundation/CVE-2020-5255.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2020-5255.yaml
• https://symfony.com/cve-2020-5255