What’s Vulnerable › Vulnerabilities

CVE-2020-5255: Prevent cache poisoning via a Response Content-Type header

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-03-30 · updated 2026-06-17
• Weakness: CWE-435

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.

Affected products

• symfony: from 4.4.0 before 4.4.7; from 5.0.0 before 5.0.7 — fixed in 4.4.7, 5.0.7

How to fix

Upgrade to a fixed version: symfony 4.4.7, 5.0.7. Check the vendor advisory for mitigations.

References

• https://github.com/symfony/symfony/commit/dca343442e6a954f96a2609e7b4e9c21ed6d74e6
• https://github.com/symfony/symfony/security/advisories/GHSA-mcx4-f5f5-4859
• 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-header
• https://github.com/symfony/symfony/commit/dca343442e6a954f96a2609e7b4e9c21ed6d74e6
• https://github.com/symfony/symfony/security/advisories/GHSA-mcx4-f5f5-4859
• 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-header

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