CVE-2026-76169fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers

Descripción

fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later.

Datos: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Se publican tal como los indican las fuentes, en inglés.

Productos y versiones afectados

Referencias y parches

• https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7 MitigationVendor Advisory
• https://cna.openjsf.org/security-advisories.html Third Party Advisory