Description
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.
Published: 2026-10-08
Score: 7.4 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-8wpc-h4q6-8fxv fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set
History

Thu, 08 Oct 2026 22:00:00 +0000

Type Values Removed Values Added
Description fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.
Title fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set
Weaknesses CWE-20
CWE-347
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'}

Subscriptions

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-08T21:44:06.843Z

Reserved: 2026-10-08T17:21:52.975Z

Link: CVE-2026-107720

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-10-08T22:17:28.090

Modified: 2026-10-08T22:17:28.227

Link: CVE-2026-107720

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

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Weaknesses
  • CWE-20

    Improper Input Validation

  • CWE-347

    Improper Verification of Cryptographic Signature