CVE-2026-107832

fastify vulnerable to header validation bypass via case-sensitive propertyNames

Published Oct 13, 2026 CVSS 3.1 · 3.7 Low EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-389g-gv7q-r4x8 fastify is vulnerable to header validation bypass via case-sensitive propertyNames
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

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

Weaknesses

Sources

Status
PUBLISHED
Assigner
openjs
Published
Updated
Oct 15, 2026, 7:14 PM
Reserved
Oct 8, 2026, 9:50 PM
Status
Awaiting Analysis
Published
Oct 13, 2026, 2:17 PM
Modified
Oct 15, 2026, 8:38 PM
Severity
Low
Public date
Oct 13, 2026, 1:23 PM