Vulnerability-Lookup

GHSA-9Q9J-Q6P8-XQ58

Vulnerability from github – Published: 2026-09-30 23:44 – Updated: 2026-09-30 23:44

Summary

fastify vulnerable to header validation bypass via incomplete schema case normalization

Details

Impact

Fastify lowercases header-schema property names before compiling the schema, because Node.js stores request header names in lowercase. That normalization was incomplete: it lowercased only top-level properties keys and the root required array, and did not lowercase the JSON Schema Draft 7 dependencies keyword (its trigger keys and dependent property names) or names in nested subschemas. As a result, a header schema that uses dependencies to require one header when another is present (for example X-Admin requiring X-Admin-Token) never matches the lowercased request headers, so the dependency assertion is silently skipped. An unauthenticated remote client can send the header that activates a privileged path while omitting the header the dependency was meant to require, bypassing a schema-enforced security control. The header schema is idiomatic, valid JSON Schema Draft 7, and no custom validator, malformed request, or misconfiguration is required.

Patches

Header-schema names are now normalized across all schema positions (properties, required, dependencies, dependentRequired, dependentSchemas, and nested subschemas). Patched in fastify 5.12.2. The fix is also included in the 6.0.0 release. Header schemas referenced through an external shared $ref (registered with addSchema) are not reached by this normalization and now emit an FSTSEC002 startup warning; inline the header schema to keep case-insensitive assertions in effect.

Workarounds

If upgrading is not immediately possible, write header-schema names in lowercase so the dependencies and other case-sensitive assertions match Node's lowercased request headers, or enforce the cross-header requirement in an onRequest or preValidation hook instead of the schema.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "fastify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.12.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84428"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-178"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-30T23:44:27Z",
    "nvd_published_at": "2026-09-04T11:17:19Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nFastify lowercases header-schema property names before compiling the schema, because Node.js stores request header names in lowercase. That normalization was incomplete: it lowercased only top-level `properties` keys and the root `required` array, and did not lowercase the JSON Schema Draft 7 `dependencies` keyword (its trigger keys and dependent property names) or names in nested subschemas. As a result, a header schema that uses `dependencies` to require one header when another is present (for example `X-Admin` requiring `X-Admin-Token`) never matches the lowercased request headers, so the dependency assertion is silently skipped. An unauthenticated remote client can send the header that activates a privileged path while omitting the header the dependency was meant to require, bypassing a schema-enforced security control. The header schema is idiomatic, valid JSON Schema Draft 7, and no custom validator, malformed request, or misconfiguration is required.\n\n### Patches\n\nHeader-schema names are now normalized across all schema positions (`properties`, `required`, `dependencies`, `dependentRequired`, `dependentSchemas`, and nested subschemas). Patched in fastify `5.12.2`. The fix is also included in the `6.0.0` release. Header schemas referenced through an external shared `$ref` (registered with `addSchema`) are not reached by this normalization and now emit an `FSTSEC002` startup warning; inline the header schema to keep case-insensitive assertions in effect.\n\n### Workarounds\n\nIf upgrading is not immediately possible, write header-schema names in lowercase so the `dependencies` and other case-sensitive assertions match Node\u0027s lowercased request headers, or enforce the cross-header requirement in an `onRequest` or `preValidation` hook instead of the schema.",
  "id": "GHSA-9q9j-q6p8-xq58",
  "modified": "2026-09-30T23:44:27Z",
  "published": "2026-09-30T23:44:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-84428"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/commit/179619c8e99d54924309b9933402151ef9af37e0"
    },
    {
      "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fastify vulnerable to header validation bypass via incomplete schema case normalization"
}

CVE-2026-84428 (GCVE-0-2026-84428)

Vulnerability from cvelistv5 – Published: 2026-09-04 10:24 – Updated: 2026-09-04 16:06

Title

fastify vulnerable to header validation bypass via incomplete schema case normalization

Summary

fastify versions before 5.12.2 implement the case-insensitive nature of HTTP header names by lowercasing names in a route's header schema before compiling it, but the transformation is incomplete: it lowercases the properties keys and the root-level required array, and does not lowercase the trigger and dependent names inside the JSON Schema Draft 7 dependencies keyword. Because Node stores request header names in lowercase, a canonical-case dependency such as requiring an authentication header whenever a privileged-mode header is present never matches, and the presence assertion is silently skipped. An unauthenticated remote client can therefore send the header that activates a privileged branch while omitting the header the dependency was meant to require, bypassing the conditional check. Users should upgrade to fastify 5.12.2 or later.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-04 16:04 UTC

CWE

CWE-178 - Improper Handling of Case Sensitivity

Assigner

openjs redhat root Scorecard

References

2 references

URL	Tags
https://github.com/fastify/fastify/security/advis…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version
fastify	fastify	Affected: 0 , < 5.12.2 (semver) Unaffected: 5.12.2 (semver)

Credits

schecthellraiser606 mcollina UlisesGascon

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JSON

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Sightings

Author	Source	Type	Date	Other

Nomenclature

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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
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