---
id: CVE-2026-107722
title: fast-jwt provides fast JSON Web Token (JWT) implementation
summary: >-
  fast-jwt provides fast JSON Web Token (JWT) implementation. From 6.2.0 until
  6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the
  key has non-whitespace content before its PEM header. In src/crypto.js,
  performDe…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-347
vendor: fast-jwt
product: fast-jwt
affected:
  - 'fast-jwt >= 6.2.0, <= 6.2.4'
patched:
  - fast-jwt 6.3.0
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T22:17:28.583'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107722'
references:
  - url: >-
      https://github.com/nearform/fast-jwt/commit/d96bbc6c5336055a6dbfa318fdbab01197264cfa
    label: security-advisories@github.com
  - url: 'https://github.com/nearform/fast-jwt/pull/632'
    label: security-advisories@github.com
  - url: 'https://github.com/nearform/fast-jwt/releases/tag/v6.3.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/nearform/fast-jwt/security/advisories/GHSA-ww5h-9m49-7xx4
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-ww5h-9m49-7xx4'
tags:
  - nvd
  - ghsa
  - npm
aliases:
  - GHSA-ww5h-9m49-7xx4
ecosystem: npm
ingestedAt: '2026-10-08T22:11:53.872Z'
---

## Overview

fast-jwt provides fast JSON Web Token (JWT) implementation. From 6.2.0 until 6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the key has non-whitespace content before its PEM header. In src/crypto.js, performDetectPublicKeyAlgorithms trims whitespace but publicKeyPemMatcher remains start-anchored, so comments, control characters, zero-width characters, or wrapper text can prevent PEM detection and reach the HMAC fallback. An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass. An asymmetric-only algorithm allowlist prevents the attack. This issue is fixed in version 6.3.0.

## Remediation

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

## Package advisory (CVE-2026-107722)

Affected packages:

- `fast-jwt >= 6.2.0, <= 6.2.4`

Patched in:

- `fast-jwt 6.3.0`

Source: https://github.com/advisories/GHSA-ww5h-9m49-7xx4