CVE-2026-35041 Details
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.
A denial-of-service vulnerability has been identified in the fast-jwt library, affecting versions 5.0.0 prior to 6.2.0. The issue arises when the audience verification option, allowedAud, is configured with a regular expression that allows for catastrophic backtracking. Since the aud claim is controlled by the attacker, a crafted JSON Web Token (JWT) can exploit this by causing excessive CPU usage during the verification process. This vulnerability is particularly concerning in authenticated contexts, such as API gateways and OAuth token validation pipelines.
Users can update to fast-jwt version 6.2.1, which addresses this vulnerability by adding a warning for unsafe regular expressions in the allowed options.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Apr 9, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf | CISA-ADP | ExploitMitigationVendor Advisory |
| https://github.com/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5de94 | [email protected] | Patch |
| https://github.com/nearform/fast-jwt/pull/595 | [email protected] | Issue TrackingPatch |
| https://github.com/nearform/fast-jwt/releases/tag/v6.2.1 | [email protected] | ProductRelease Notes |
| https://github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf | [email protected] | ExploitMitigationVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-1333 | Inefficient Regular Expression Complexity | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| nearform fast-jwt | >= 5.0.0, < 6.2.1 |
CPE
Remediation
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Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Apr 14, 2026 | Initial Analysis | [email protected] |
| Apr 9, 2026 | CVE Modified | CISA-ADP |
| Apr 9, 2026 | New CVE Received | [email protected] |