Vulnerability in Fastify Fastify\/middie
CVE-2026-85184
@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped. An unauthenticated network attacker can use this to bypass path-based access controls in a Fastify application that relies on middie for those controls. Users should upgrade to @fastify/middie 9.3.4 or later.
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: 0.005 (43.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 43.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Third Party Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-85184?
- CVE-2026-85184 is a critical-severity vulnerability in Fastify Fastify\/middie, classified under CWE-436. CVSS score: 9.1/10. Published 2026-09-04.
- How severe is CVE-2026-85184?
- Critical severity. CVSS v3 base score is 9.1 out of 10.