Impact: Fastify applications using schema.body.content for per-content-type body validation can have validation bypassed entirely by prepending a space to the Content-Type header. The body is still parsed correctly but schema validation is skipped. This is a regression introduced in fastify >= 5.3.2 by the fix for CVE-2025-32442 Patches: Upgrade to fastify v5.8.5 or later. Workarounds: None. Upgrade to the patched version.

Fastify is a fast and low overhead web framework, for Node.js. In versions 5.0.0 to 5.3.0 as well as version 4.29.0, applications that specify different validation strategies for different content types have a possibility to bypass validation by providing a _slightly altered_ content type such as with different casing or altered whitespacing before `;`. This was patched in v5.3.1, but the initial patch did not cover all problems. This has been fully patched in v5.3.2 and v4.29.1. A workaround involves not specifying individual content types in the schema.