CVE-2026-35041: CWE-1333: Inefficient Regular Expression Complexity in nearform fast-jwt
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.
AI Analysis
Technical Summary
The fast-jwt library, used for JSON Web Token implementation, contains a denial-of-service vulnerability in versions from 5.0.0 up to but not including 6.2.1. When the allowedAud verification option is set using a regular expression, the library evaluates the attacker-controlled 'aud' claim against this regex. Crafted JWTs can exploit inefficient regex evaluation leading to catastrophic backtracking and excessive CPU usage. This vulnerability is tracked as CWE-1333 and has a CVSS 3.1 base score of 4.2 (medium severity). The issue is resolved in fast-jwt version 6.2.1.
Potential Impact
Successful exploitation results in a denial-of-service condition due to high CPU consumption during JWT verification. There is no impact on confidentiality or integrity, only availability is affected. The vulnerability requires high attack complexity and privileges with user interaction, limiting its exploitability.
Mitigation Recommendations
Upgrade fast-jwt to version 6.2.1 or later where this vulnerability is fixed. Since the vendor advisory indicates the issue is resolved in 6.2.1, applying this official fix is the recommended remediation. No alternative mitigations or workarounds are provided.
CVE-2026-35041: CWE-1333: Inefficient Regular Expression Complexity in nearform fast-jwt
Description
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The fast-jwt library, used for JSON Web Token implementation, contains a denial-of-service vulnerability in versions from 5.0.0 up to but not including 6.2.1. When the allowedAud verification option is set using a regular expression, the library evaluates the attacker-controlled 'aud' claim against this regex. Crafted JWTs can exploit inefficient regex evaluation leading to catastrophic backtracking and excessive CPU usage. This vulnerability is tracked as CWE-1333 and has a CVSS 3.1 base score of 4.2 (medium severity). The issue is resolved in fast-jwt version 6.2.1.
Potential Impact
Successful exploitation results in a denial-of-service condition due to high CPU consumption during JWT verification. There is no impact on confidentiality or integrity, only availability is affected. The vulnerability requires high attack complexity and privileges with user interaction, limiting its exploitability.
Mitigation Recommendations
Upgrade fast-jwt to version 6.2.1 or later where this vulnerability is fixed. Since the vendor advisory indicates the issue is resolved in 6.2.1, applying this official fix is the recommended remediation. No alternative mitigations or workarounds are provided.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-03-31T21:06:06.428Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d7d5661cc7ad14daeeafcd
Added to database: 4/9/2026, 4:35:50 PM
Last enriched: 4/9/2026, 4:50:50 PM
Last updated: 5/25/2026, 2:41:24 AM
Views: 117
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