What is CVE-2026-33808?

CVE-2026-33808 is a critical-severity vulnerability in Fastify @Fastify/express, classified under CWE-436. CVSS score: 9.1/10. Published 2026-04-15.

How severe is CVE-2026-33808?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in Fastify @Fastify/express

CVE-2026-33808

Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled. This allows complete bypass of path-scoped authentication middleware via dup…

EPSS: 0.002 (37.0th 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/express — versions 0, 4.0.5
Fastify Fastify\/express

Weakness classification (CWE)

CWE-436

References

ce714d77-add3-4f53-aff5-83d477b104bb (Exploit, Mitigation, Vendor Advisory)
ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)

Frequently asked questions

What is CVE-2026-33808?: CVE-2026-33808 is a critical-severity vulnerability in Fastify @Fastify/express, classified under CWE-436. CVSS score: 9.1/10. Published 2026-04-15.
How severe is CVE-2026-33808?: Critical severity. CVSS v3 base score is 9.1 out of 10.