@fastify/static evaluates the allowedPath callback before normalizing dot segments and duplicate path separators in the pathname used for file resolution. Versions up to and including 10.1.1 are affected. An unauthenticated attacker can bypass allowedPath restrictions by requesting equivalent non-canonical pathnames, causing files that were intended to be denied to be served anyway. The bypass does not allow access outside the configured static root by itself, it defeats path-based filtering only. The issue is patched in @fastify/static 10.1.2.

@fastify/static vulnerable to Authorization Bypass via Non-Canonical URL Paths