What’s Vulnerable › Vulnerabilities

CVE-2026-107720: fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-08 · updated 2026-10-09
• Weakness: CWE-20

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.

Affected products

• nearform fast-jwt: before 6.3.1

References

• https://github.com/nearform/fast-jwt/commit/e22a151e83bf6d5e54e281216982d204d5665534
• https://github.com/nearform/fast-jwt/pull/649
• https://github.com/nearform/fast-jwt/releases/tag/v6.3.1
• https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv
• https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv

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