nearform fast-jwt up to 6.2.0 JWT redos

Summaryinfo

A vulnerability classified as problematic has been found in nearform fast-jwt up to 6.2.0. This vulnerability affects unknown code of the component JWT Handler. The manipulation leads to redos. This vulnerability is traded as CVE-2026-35041. It is possible to initiate the attack remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in nearform fast-jwt up to 6.2.0. It has been rated as problematic. This issue affects some unknown processing of the component JWT Handler. The manipulation with an unknown input leads to a redos vulnerability. Using CWE to declare the problem leads to CWE-1333. The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles. Impacted is availability. The summary by CVE is:

fast-jwt provides fast JSON Web Token (JWT) implementation. From 5.0.0 to 6.2.0, a denial-of-service condition exists in fast-jwt when the allowedAud verification option is configured using a regular expression. Because the aud claim is attacker-controlled and the library evaluates it against the supplied RegExp, a crafted JWT can trigger catastrophic backtracking in the JavaScript regex engine, resulting in significant CPU consumption during verification. This vulnerability is fixed in 6.2.1.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-35041 since 03/31/2026. The exploitation is known to be difficult. The attack may be initiated remotely. Additional levels of successful authentication are needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1449.003 according to MITRE ATT&CK.

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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