CVE-2026-6270

CRITICAL 9.1

@fastify/middie vulnerable to middleware authentication bypass in child plugin scopes

CVSS Score

9.1

EPSS Score

0.0%

EPSS Percentile

0th

@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.

CWE	CWE-436
Vendor	@fastify/middie
Product	@fastify/middie
Published	Apr 16, 2026
Last Updated	Apr 16, 2026

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CVSS v3 Breakdown

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

Attack Vector

Attack Complexity

Privileges Required

User Interaction

Scope

Confidentiality

Integrity

Availability

Affected Versions

@fastify/middie / @fastify/middie

0 < 9.3.2

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c github.com: https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5w cna.openjsf.org: https://cna.openjsf.org/security-advisories.html

Credits

🔍 FredKSchott climba03003 UlisesGascon