[ CVE-2026-84428 · Published 4 Sep 2026 ]
fastify vulnerable to header validation bypass via incomplete schema case normalization
[ Description ]Official description
fastify versions before 5.12.2 implement the case-insensitive nature of HTTP header names by lowercasing names in a route's header schema before compiling it, but the transformation is incomplete: it lowercases the properties keys and the root-level required array, and does not lowercase the trigger and dependent names inside the JSON Schema Draft 7 dependencies keyword. Because Node stores request header names in lowercase, a canonical-case dependency such as requiring an authentication header whenever a privileged-mode header is present never matches, and the presence assertion is silently skipped. An unauthenticated remote client can therefore send the header that activates a privileged branch while omitting the header the dependency was meant to require, bypassing the conditional check. Users should upgrade to fastify 5.12.2 or later.
[ Fixes ]Fixes and patches
- fastify 5.12.2Fixed version · GitHub Advisories · npm package fastify: upgrade to 5.12.2 or later (affected < 5.12.2)
[ Packages ]Affected open-source packages
- fastify npmAffected < 5.12.2 · fixed in 5.12.2 · GHSA-9q9j-q6p8-xq58