CVE-2026-107722

Deferred Deferred - Pending Action

JWT Authentication Bypass in fast-jwt

Publication date: 2026-10-08

Last updated on: 2026-10-08

Assigner: GitHub, Inc.

Description

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.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-08

Last Modified

2026-10-08

Generated

2026-10-09

AI Q&A

2026-10-09

EPSS Evaluated

N/A

NVD

CVE-2026-107722

Affected Vendors & Products

Vendor	Product	Version / Range
nearform	fast-jwt	>= 6.2.0, < 6.3.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-347	The product does not verify, or incorrectly verifies, the cryptographic signature for data.

Attack-Flow Graph

Executive Summary

fast-jwt versions 6.2.0 to 6.3.0 incorrectly classify RSA public keys as HMAC secrets if the key contains non-whitespace text before the PEM header. This happens because the public key detection fails to recognize the key format, leading the system to use HMAC instead of RSA for signing. Attackers can exploit this by signing arbitrary HS256 tokens with the public key material, bypassing authentication or authorization checks.

Impact Analysis

If you use fast-jwt versions between 6.2.0 and 6.3.0, an attacker could forge JWT tokens to impersonate users or escalate privileges. This could allow unauthorized access to sensitive data or actions protected by the JWT authentication system. The impact is high as it affects confidentiality, integrity, and availability of the system.

Compliance Impact

This vulnerability could lead to unauthorized access to personal or sensitive data, violating GDPR's data protection principles and HIPAA's security requirements. Non-compliance may result in legal penalties, reputational damage, and loss of trust. Organizations must ensure JWT implementations are secure to meet these regulatory standards.

Mitigation Strategies

Upgrade fast-jwt to version 6.3.0 or later to address the vulnerability. Ensure only asymmetric algorithms are allowed in JWT verification to prevent HMAC fallback abuse.

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