CVE-2026-84469

Описание

fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.

A flaw was found in fastify. An unauthenticated remote attacker can bypass request validation by exploiting how fastify processes boolean false schemas. When an application intends to deny all input by assigning 'false' to a route's schema, fastify incorrectly treats it as a missing schema and fails to compile a validator. This allows the attacker to reach handlers that should be unreachable, leading to unauthorized state changes or the execution of disabled operations.