CVE-2026-112712

About vulnerability

@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.

Affected product:

Fastify , callstack-repack , callstack-repack-plugin-expo-modules , callstack-repack-plugin-nativewind , callstack-repack-plugin-reanimated , ecosystem , nestjs-platform-fastify , repack , rock-js-plugin-repack

Affected packages:

@fastify/middie @ 9.0.3 (+96 more)