CVE-2026-2880: Fastify Fastify/middie

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

A vulnerability in @fastify/middie versions < 9.2.0 can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)). When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.

Affected products

• Fastify Fastify/middie: before 9.2.0 (fixed in 9.2.0)

Published 2026-02-27. Last modified 2026-06-17.