Description
fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.
Published: 2026-09-04
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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History

Fri, 04 Sep 2026 12:45:00 +0000

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

Fri, 04 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-1287
References
Metrics threat_severity

None

threat_severity

Important


Fri, 04 Sep 2026 10:15:00 +0000

Type Values Removed Values Added
Description fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.
Title fastify vulnerable to request validation bypass via skipped boolean false schemas
Weaknesses CWE-20
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-09-04T09:59:36.406Z

Reserved: 2026-09-01T20:07:12.965Z

Link: CVE-2026-84469

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-04T10:17:13.677

Modified: 2026-09-04T10:17:13.677

Link: CVE-2026-84469

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-04T09:59:36Z

Links: CVE-2026-84469 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-04T12:30:17Z

Weaknesses
  • CWE-1287

    Improper Validation of Specified Type of Input

  • CWE-20

    Improper Input Validation