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.
What this means for your business
- It affects Fastify\/Middie. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 0.5% chance of attack attempts being seen in the next 30 days, ranking above 42% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Fastify\/Middie, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Fastnexa security experts
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Scoring
- CVSS
- 9.1 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N- Weakness
- CWE-436
- Assigned by
- ce714d77-add3-4f53-aff5-83d477b104bb
Dates
- Published
- 2026-09-04
- Last modified
- 2026-09-15
- Sources
- NVD
Affected products
- Fastify Fastify\/Middie9.1.0 - 9.3.4
As listed in the NVD configuration data. Not a statement about your estate.