What is CVE-2026-33804?

CVE-2026-33804 is a high-severity vulnerability in Fastify Fastify\/middie, classified under CWE-436. CVSS score: 7.4/10. Published 2026-04-16.

How severe is CVE-2026-33804?

High severity. CVSS v3 base score is 7.4 out of 10.

Vulnerability in Fastify Fastify\/middie

CVE-2026-33804

@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization perf…

EPSS: 0.001 (21.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:N/AC:H/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 (Mitigation, Vendor Advisory)
ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)

Frequently asked questions

What is CVE-2026-33804?: CVE-2026-33804 is a high-severity vulnerability in Fastify Fastify\/middie, classified under CWE-436. CVSS score: 7.4/10. Published 2026-04-16.
How severe is CVE-2026-33804?: High severity. CVSS v3 base score is 7.4 out of 10.