nearform fast-jwt up to 6.3.0 Verification createVerifier key/algorithms input validation

Summaryinfo

A vulnerability identified as critical has been detected in nearform fast-jwt up to 6.3.0. This vulnerability affects the function createVerifier of the component Verification. This manipulation of the argument key/algorithms causes input validation. This vulnerability is tracked as CVE-2026-107720. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in nearform fast-jwt up to 6.3.0. It has been declared as critical. Affected by this vulnerability is the function createVerifier of the component Verification. The manipulation of the argument key/algorithms with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-107720 since 10/08/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 6.3.1 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-95344). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• nearform

Name

• fast-jwt

Version

• 6.0
• 6.1
• 6.2
• 6.3.0

Website

• Product: https://github.com/nearform/fast-jwt/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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