CVE-2025-64166: Mercurius is a GraphQL adapter for Fastify

Routine

MEDIUM 5.4UPGRADE

CVE-2025-64166 is a medium-severity flaw (CVSS 5.4) affecting mercurius. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 b

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 94%)
CISA exploited list	No
Weakness	CWE-352
Published	2026-03-05
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: mercurius project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-05 16:16 UTCPublished CVE record published
2026-06-17 09:53 UTCUpdated Record last modified

mercurius project mercurius UPGRADE

Affected: < 16.4.0

Fixed in: 16.4.0

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls mercurius

2. UPGRADE to 16.4.0

npm install mercurius@">=16.4.0"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-64166?

mercurius: upgrade to 16.4.0. Exact commands for each OS are on this page.

Is CVE-2025-64166 being exploited?

CVE-2025-64166 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-64166 affect?

CVE-2025-64166 affects mercurius. Severity is medium (CVSS 5.4). 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 wi

How urgent is CVE-2025-64166?

Priority 25/100. Public exploit reference

Related CVEs

CVE-2026-30241 HIGH 8.2 UPGRADE Mercurius is a GraphQL adapter for Fastify

References

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