CVE-2026-6270: @fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers…

PriorityP264critical9.1CVSS 3.1

AVNACLPRNUINSUCHIHAN

EPSS

0.50%

38.9th percentile

@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.

Affected

3 ranges

Vendor	Product	Version range	Fixed in
fastify	fastify_middie	< 9.3.2	9.3.2
fastify	middie	>= 0 < 9.3.2	9.3.2
fastify	middie_fastify_middie	< 9.3.2	9.3.2

CVSS provenance

nvdv3.19.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

ghsa9.1CRITICAL

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