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9.1
CVE-2026-85184: Fastify middie may skip authentication on specific requests
CVE-2026-85184 · published 1 day ago
Summary
If you use Fastify with the @fastify/middie package version 9.1.0 through 9.3.3, a specially crafted request can avoid the middleware that checks login or permissions. This lets an unauthenticated user reach parts of your app that should be protected. Upgrade to version 9.3.4 or newer to close the gap.
What to do
- Update @fastify/middie @fastify/middie to version 9.3.4 or later.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| @fastify/middie | @fastify/middie | < 9.3.4 |
Original advisory text
@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 reques...
@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.
Severity
9.1
Critical
CVSS 3.1: 9.1 (NVD)
Exploitation
EPSS <1%
Type
CWE-436Interpretation Conflict
Timeline
Published4 Sep 2026
Updated4 Sep 2026
First seen4 Sep 2026
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