nearform fast-jwt up to 6.2.0 verify comparison

Summaryinfo

A vulnerability described as problematic has been identified in nearform fast-jwt up to 6.2.0. This affects the function verify. Executing a manipulation of the argument allowedAud/allowedIss/allowedSub/allowedJti/allowedNonce can lead to comparison. This vulnerability appears as CVE-2026-35040. The attack may be performed from remote. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in nearform fast-jwt up to 6.2.0. It has been declared as problematic. This vulnerability affects the function verify. The manipulation of the argument allowedAud/allowedIss/allowedSub/allowedJti/allowedNonce with an unknown input leads to a comparison vulnerability. The CWE definition for the vulnerability is CWE-697. The product compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses. As an impact it is known to affect availability. CVE summarizes:

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unintended behaviours. This is because some modifiers are stateful and will cause failures in every second verification attempt regardless of the validity of the token provided. Such modifiers are /g (global matching) and /y (sticky matching). This does NOT allow invalid tokens to be accepted, only for valid tokens to be improperly rejected in some configurations. Instead it causes 50% of valid authentication requests to fail in an alternating pattern. This vulnerability is fixed in 6.2.1.

The advisory is available at github.com. This vulnerability was named CVE-2026-35040 since 03/31/2026. The exploitation appears to be easy. The attack can be initiated remotely. Technical details are known, but there is no available exploit.

Upgrading to version 6.2.1 eliminates this vulnerability.

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Productinfo

Vendor

• nearform

Name

• fast-jwt

Version

• 6.0
• 6.1
• 6.2.0

Website

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

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