Fastify onRegister Function Use-After-Free

The vulnerability of the onRegister function in the Fastify framework, a Node.js software platform, is related to the occurrence of interpretation conflicts when processing HTTP headers’ names and values. Exploiting this vulnerability allows an attacker to compromise the confidentiality and...

Improper Access Control

@fastify/express is vulnerable to Improper Access Control. The vulnerability is due to incorrect path handling in the onRegister function, where middleware paths are duplicated when inherited by child plugins, causing them to not match incoming requests and resulting in bypass of security control...

@fastify/express's middleware path doubling causes authentication bypass in child plugin scopes

Summary @fastify/express v4.0.4 contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. This results in complete bypass of Express middleware security controls for all routes defined within child plugin scopes that share ...

CVE-2026-33807

@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time,...