---
id: CVE-2026-107720
title: fast-jwt provides fast JSON Web Token (JWT) implementation
summary: >-
  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
  prepar…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-20
  - CWE-347
vendor: fast-jwt
product: fast-jwt
affected:
  - fast-jwt <= 6.3.0
patched:
  - fast-jwt 6.3.1
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T22:17:28.227'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107720'
references:
  - url: >-
      https://github.com/nearform/fast-jwt/commit/e22a151e83bf6d5e54e281216982d204d5665534
    label: security-advisories@github.com
  - url: 'https://github.com/nearform/fast-jwt/pull/649'
    label: security-advisories@github.com
  - url: 'https://github.com/nearform/fast-jwt/releases/tag/v6.3.1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-8wpc-h4q6-8fxv'
tags:
  - nvd
  - ghsa
  - npm
aliases:
  - GHSA-8wpc-h4q6-8fxv
ecosystem: npm
ingestedAt: '2026-10-08T22:11:53.872Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-107720)

Affected packages:

- `fast-jwt <= 6.3.0`

Patched in:

- `fast-jwt 6.3.1`

Source: https://github.com/advisories/GHSA-8wpc-h4q6-8fxv