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.

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 wi…

EPSS: 0.001 (24.6th percentile) — read the EPSS interpretation.

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.

Affected products

Fastify Fastify\/middie
@Fastify/middie — versions 0, 9.3.2

Weakness classification (CWE)

CWE-436

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.