All vulnerabilities
CVE-2026-112712GHSA-5p92-8765-9fv8

@fastify/middie vulnerable to path-scoped middleware bypass via scope prefix mismatch

@fastify/middie @fastify/middieFrameworks
CVSS
9.1Critical
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.31%Chance of exploitation activity in the next 30 days, higher than 23% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in9.3.6Fixed versionCVE List
Published20 Oct 2026Updated 20 Oct 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

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.

Text from CVE List

Affected versions 2

  • @fastify/middieaffected: 9.0.0 before 9.3.6CVE List
  • @fastify/middieunaffected: 9.3.6CVE List

References 2