AIKIDO-2026-94607
fastify is vulnerable to Header Validation Bypass
75
High Risk
This Affects:
fastifyTL;DR
Fastify's header-schema normalization lowercases top-level properties keys and the root required array but leaves dependencies, related keywords, and nested subschemas case-sensitive. An unauthenticated client can send a mixed-case header that activates a privileged path while omitting a dependent header that the schema should require, bypassing a schema-enforced security control. The fix normalizes header names throughout inline schemas and warns when an external $ref cannot be normalized.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your header schemas use mixed-case names in dependencies or nested subschemas.
Background info
fastify is vulnerable to Header Validation Bypass in versions 0.0.1 - 5.12.1.
How to fix this
Upgrade the fastify library to the patch version.
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