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 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.

The following products are affected by CVE-2026-6270 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-6270.

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