CVE-2026-84428

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://cna.openjsf.org/security-advisories.html	Third Party Advisory
https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:*

History

No history.

Information

Published : 2026-09-04 11:17

Updated : 2026-09-15 19:54

NVD link : CVE-2026-84428

Mitre link : CVE-2026-84428

CVE.ORG link : CVE-2026-84428

JSON object : View

Products Affected

fastify

fastify

CWE

CWE-178

Improper Handling of Case Sensitivity

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