CVE-2026-85184: fastify fastify\/middie

CVSS 9.1 (critical) · published 2026-09-04

@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.

Affected products (NVD): fastify fastify\/middie

Fixed in (NVD): 9.3.4

Weakness: CWE-436

Source: NVD CVE-2026-85184

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/middie/security/advisories/GHSA-hx87-8wv7-pjv8

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