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fastify vulnerable to request validation bypass via skipped boolean false schemas

Type: advisorySources: OSV

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.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-84469
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 18:36 UTC · Revision 1

Source evidence

fastify vulnerable to request validation bypass via skipped boolean false schemas

core-osv · Original source

Published 4 Sept 2026, 09:59 UTC

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.

osv:CVE-2026-84469
Complete source record
{
  "id": "b2008b864f5dd0d3a042ad682c13722e71eed30c49aadd9da56e717dc0dfd275",
  "url": "https://osv.dev/vulnerability/CVE-2026-84469",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fastify vulnerable to request validation bypass via skipped boolean false schemas",
    "summary": "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.",
    "evidence": "osv:CVE-2026-84469",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-84469",
      "aliases": [
        "CVE-2026-84469",
        "GHSA-hwr6-493r-vm6h"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
        }
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      "affected": [
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                    "source": "AFFECTED_FIELD",
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                    "range": [
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      "provider": "osv",
      "references": [
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        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84469.json",
        "https://github.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-84469"
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    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 505753,
  "published_at": "2026-09-04T09:59:36.406+00:00"
}