---
id: "CVE-2026-112712"
kind: "vulnerability"
aliases: ["CVE-2026-112712"]
title: "Fastify middie: path-scoped middleware silently skipped, bypassing auth checks"
severity: "critical"
cvss: 9.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["api-servers", "fastify", "node", "package"]
not_affected_if: ["default-config"]
published_at: "2026-10-20T21:17:17+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-23T22:39:14+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112712", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# Fastify middie: path-scoped middleware silently skipped, bypassing auth checks

In @fastify/middie versions 9.0.0 through 9.3.5, path-scoped middleware can be silently skipped while the route handler still runs. An unauthenticated request can therefore bypass authentication, authorization, or rate limiting that was attached as middleware.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

Check the installed version: npm ls @fastify/middie

## Fix

Upgrade @fastify/middie to 9.3.6 or later.
As a workaround, move authorization checks into a Fastify preHandler hook.

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112712

## From the sources

@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.

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