Vulnerability Description
@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.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Fastify | Fastify\/Middie | < 9.3.2 |
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.htmlVendor Advisory
- https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7pExploitMitigationVendor Advisory
- https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5wVendor Advisory
FAQ
What is CVE-2026-6270?
CVE-2026-6270 is a vulnerability with a CVSS score of 9.1 (CRITICAL). @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 sc...
How severe is CVE-2026-6270?
CVE-2026-6270 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-6270?
Check the references section above for vendor advisories and patch information. Affected products include: Fastify Fastify\/Middie.