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CVE-2026-112712

9.1 CRITICALpublic exploit available

Published 2026-10-20 · Updated 2026-10-22

AI risk analysis

Summary
A path construction bug in @fastify/middie versions 9.0.0–9.3.5 caused path-scoped middleware (e.g., auth, rate limiting) to be silently skipped when the scope prefix ended with a slash or when using array/non-leading-slash mount paths, allowing unauthenticated requests to bypass intended protections.
Exploitability
Trivial to exploit remotely without authentication or user interaction; requires only crafting a request to a vulnerable path pattern.
Blast radius
Any application using affected versions of @fastify/middie with path-scoped middleware is at risk of complete authentication/authorization bypass, potentially exposing sensitive endpoints and data.
Detection
No reliable host or network indicator is derivable from the published description.
Prioritized remediation
Upgrade to @fastify/middie version 9.3.6 or later immediately.
auth-bypassmiddlewarenodejsfastifypath-traversal

Analysis generated locally by garnet-coder (no data left the box). AI-assisted — verify against primary sources before acting.

NVD description

@fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when the scope prefix ended in a slash, and also for array mount paths and for mount paths written without a leading slash. When the two paths disagreed, the middleware was silently skipped while the route handler still ran, so path-scoped middleware such as authentication, authorization, or rate limiting could be bypassed by a single unauthenticated request. The issue is fixed in @fastify/middie 9.3.6, and users should upgrade to 9.3.6 or later. As a workaround, enforce authorization in a Fastify hook such as preHandler that runs after the router has resolved the request.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Weaknesses

CWE-436

Public exploit & PoC references

All references

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

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