Vulnerability in Fastify Fastify\/middie
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (47.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 47th percentile — 47.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.006 · change: +0.001
Affected products
- Fastify Fastify\/middie
- @Fastify/middie — versions 0, 9.3.2
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Exploit, Mitigation, Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-6270?
- CVE-2026-6270 is a critical-severity vulnerability in Fastify Fastify\/middie, classified under CWE-436. CVSS score: 9.1/10. Published 2026-04-16.
- How severe is CVE-2026-6270?
- Critical severity. CVSS v3 base score is 9.1 out of 10.