@fastify/static vulnerable to route guard bypass via path traversal

Summary

@fastify/static up to and including version 10.1.0 fails to reject dot-dot path segments in request pathnames before the file-resolution stage. This is a bypass of the earlier fix for CVE-2026-6414, which only covered encoded forward slashes. Because the underlying send library normalizes dot segments before applying its own path-traversal guard, an unauthenticated attacker can bypass any route-scoped middleware and read files inside the static root that live under the guarded URL prefix. The bypass does not allow access outside the configured static root by itself, it defeats route-guard filtering only. The issue is patched in @fastify/static 10.1.1.

Timeline

1. Jul 23, 2026, 3:01 AM UTCCVE published
2. Jul 23, 2026, 2:14 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Jul 23, 2026, 2:14 PM UTCRecord last updated

Affected versions

• @fastify/static @fastify/static

  fixed in 10.1.1

• @fastify/staticnpm

  fixed in 10.1.1

References 2