CVE-2020-5255

Name: CVE-2020-5255
Creator: NVD / NIST
Published: 2020-03-30T20:15:19.57+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 1.30%

Last modified Jun 17, 2026

CVE-2020-5255 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. In Symfony before versions 4.4.7 and 5.0.7, when a `Response` does not contain a `Content-Type` header, affected versions of Symfony can fallback 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 prevent the use of the website by other users. EPSS estimates a 1.30% chance of exploitation in the next 30 days.

Description

In Symfony before versions 4.4.7 and 5.0.7, when a `Response` does not contain a `Content-Type` header, affected versions of Symfony can fallback 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 prevent the use of the website by other users. This has been patched in versions 4.4.7 and 5.0.7.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS Probability

1.30%

66.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Sensiolabs	Symfony	>= 4.4.0, < 4.4.7
Sensiolabs	Symfony	>= 5.0.0, < 5.0.7

References

https://github.com/symfony/symfony/commit/dca343442e6a954f96a2609e7b4e9c21ed6d74e6Patch, Third Party Advisory
https://github.com/symfony/symfony/security/advisories/GHSA-mcx4-f5f5-4859Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/C36JLPHUPKDFAX6D5WYFC4ALO2K7RDUQ/
https://symfony.com/blog/cve-2020-5255-prevent-cache-poisoning-via-a-response-content-type-headerThird Party Advisory
https://github.com/symfony/symfony/commit/dca343442e6a954f96a2609e7b4e9c21ed6d74e6Patch, Third Party Advisory
https://github.com/symfony/symfony/security/advisories/GHSA-mcx4-f5f5-4859Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/C36JLPHUPKDFAX6D5WYFC4ALO2K7RDUQ/
https://symfony.com/blog/cve-2020-5255-prevent-cache-poisoning-via-a-response-content-type-headerThird Party Advisory

Timeline

Published: Mar 30, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-5255?

How severe is CVE-2020-5255?

CVE-2020-5255 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 1.30% probability of exploitation in the next 30 days.

How do I fix CVE-2020-5255?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2020-5255?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST