fastify is a fast and low overhead web framework for Node.js. In versions 5.12.2 through 5.12.5, the routine that lowercases header names declared in a route schema does not lowercase the enum or const header names nested inside a propertyNames subschema. As a result, a header allow-list or deny-list written with canonical (non-lowercase) casing never matches the incoming lowercased header, so a restricted header passes validation and reaches the route handler. An attacker can therefore bypass a case-sensitive header validation rule and smuggle a forbidden header past the schema, affecting the integrity of request handling. The issue is fixed in fastify 5.12.6, and users should upgrade to 5.12.6 or later. There is no workaround other than upgrading, though applications can declare header names in lowercase to avoid the mismatch.

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History

Wed, 14 Oct 2026 00:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Low


Tue, 13 Oct 2026 15:00:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify
Vendors & Products Fastify
Fastify fastify

Tue, 13 Oct 2026 13:45:00 +0000

Type Values Removed Values Added
Description fastify is a fast and low overhead web framework for Node.js. In versions 5.12.2 through 5.12.5, the routine that lowercases header names declared in a route schema does not lowercase the enum or const header names nested inside a propertyNames subschema. As a result, a header allow-list or deny-list written with canonical (non-lowercase) casing never matches the incoming lowercased header, so a restricted header passes validation and reaches the route handler. An attacker can therefore bypass a case-sensitive header validation rule and smuggle a forbidden header past the schema, affecting the integrity of request handling. The issue is fixed in fastify 5.12.6, and users should upgrade to 5.12.6 or later. There is no workaround other than upgrading, though applications can declare header names in lowercase to avoid the mismatch.
Title fastify vulnerable to header validation bypass via case-sensitive propertyNames
Weaknesses CWE-178
References
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-10-13T13:23:24.217Z

Reserved: 2026-10-08T21:50:49.357Z

Link: CVE-2026-107832

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-13T14:17:19.167

Modified: 2026-10-13T14:17:19.167

Link: CVE-2026-107832

cve-icon Redhat

Severity : Low

Publid Date: 2026-10-13T13:23:24Z

Links: CVE-2026-107832 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-13T14:45:10Z

Weaknesses