CVE-2026-84469: Fastify Fastify Vulnerable To Request Validation Vulnerability

HIGH
Advisory Identifier: GHSA-hwr6-493r-vm6h
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CVSS 7.5
CWE-20
Published
Advisory Summary

CVE-2026-84469 is a HIGH (CVSS 7.5) fastify vulnerable to request validation vulnerability (CWE-20: Improper Input Validation) affecting Fastify libraries in the npm ecosystem. The issue involves fastify vulnerable to request validation bypass via skipped boolean false schemas. Remediation is available by upgrading affected packages to version 5.12.2.

CVE-2026-84469 at a Glance

CVE Identifier CVE-2026-84469
GHSA Identifier GHSA-hwr6-493r-vm6h
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-20: Improper Input Validation
Affected Product Fastify
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-84469

To remediate this vulnerability, upgrade all affected Fastify dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

fastify fixed: 5.12.2 
npm install fastify@5.12.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls fastify

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-84469, inspect your project dependencies using npm:

npm ls fastify

Analyze the terminal output to locate any version of Fastify in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 5.12.2), your application is affected.

Note: The npm ls fastify command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Fastify, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Fastify decided whether to validate a request part by checking its schema for JavaScript truthiness. JSON Schema Draft 7 defines the boolean `false` as a valid schema that rejects every instance, but because `false` is falsy, a route that set `body`, `querystring`, `params`, or `headers` to `false` had that part left uncompiled: no validator was attached and the request reached the handler. An application that used `false` as a deny-all schema to make a route unreachable was therefore fully bypassed, and an unauthenticated remote client could reach the handler with any input. The same applied to the documented `query` alias for `querystring`. This is a complete bypass rather than a weak-schema issue, since `false` is the strongest JSON Schema assertion and must always fail. ### Patches Request-part schemas are now selected by an explicit presence check rather than truthiness, so a boolean `false` (or `true`) schema is compiled and enforced, including through the `query` alias. Patched in fastify `5.12.2`. The fix is also included in the `6.0.0` release. ### Workarounds If upgrading is not immediately possible, express a deny-all request schema with an always-failing object schema instead of the boolean `false` (for example `{ "not": {} }`), or reject the request in an `onRequest` hook.

CVE-2026-84469 Affected Fastify Versions

1 component(s)
Fixed Versions:
5.12.2
Product / Package Ecosystem Affected Versions Fixed Version
fastify
npm/fastify
npm
< 5.12.2
5.12.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h
NVD — CVE-2026-84469 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84469
Security Fix Commit FIX COMMIT
https://github.com/fastify/fastify/commit/7de6e81697778f9f41bd327a3b1c5c9a0d9637b4
Fastify Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Fastify Source Repository REPOSITORY
https://github.com/fastify/fastify
Fastify Release RELEASE
https://github.com/fastify/fastify/releases/tag/v5.12.2

Frequently Asked Questions

What is CVE-2026-84469?
CVE-2026-84469 is a security vulnerability in Fastify involving fastify vulnerable to request validation bypass via skipped boolean false schemas under CWE-20: Improper Input Validation.
Which Fastify versions are affected?
Affected versions include releases prior to 5.12.2 across affected packages: fastify.
What version fixes CVE-2026-84469?
Upgrading to 5.12.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is fastify affected?
Yes, fastify is affected in releases prior to 5.12.2. Upgrade your dependency to 5.12.2 or later.
What is the CVSS score of CVE-2026-84469?
CVE-2026-84469 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2026-84469?
CVE-2026-84469 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check npm dependencies for CVE-2026-84469?
Run the dependency tree command: 'npm ls fastify'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hwr6-493r-vm6h",
  "modified" : "2026-09-30T23:44:58Z",
  "published" : "2026-09-30T23:44:58Z",
  "aliases" : [ "CVE-2026-84469" ],
  "summary" : "fastify vulnerable to request validation bypass via skipped boolean false schemas",
  "details" : "### Impact\n\nFastify decided whether to validate a request part by checking its schema for JavaScript truthiness. JSON Schema Draft 7 defines the boolean `false` as a valid schema that rejects every instance, but because `false` is falsy, a route that set `body`, `querystring`, `params`, or `headers` to `false` had that part left uncompiled: no validator was attached and the request reached the handler. An application that used `false` as a deny-all schema to make a route unreachable was therefore fully bypassed, and an unauthenticated remote client could reach the handler with any input. The same applied to the documented `query` alias for `querystring`. This is a complete bypass rather than a weak-schema issue, since `false` is the strongest JSON Schema assertion and must always fail.\n\n### Patches\n\nRequest-part schemas are now selected by an explicit presence check rather than truthiness, so a boolean `false` (or `true`) schema is compiled and enforced, including through the `query` alias. Patched in fastify `5.12.2`. The fix is also included in the `6.0.0` release.\n\n### Workarounds\n\nIf upgrading is not immediately possible, express a deny-all request schema with an always-failing object schema instead of the boolean `false` (for example `{ \"not\": {} }`), or reject the request in an `onRequest` hook.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fastify"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.12.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84469"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fastify/commit/7de6e81697778f9f41bd327a3b1c5c9a0d9637b4"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fastify/fastify"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fastify/releases/tag/v5.12.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-30T23:44:58Z",
    "nvd_published_at" : "2026-09-04T10:17:13Z"
  }
}