ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification

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Summary

CVECVE-2026-35041
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-09 16:16:27 UTC
Updated2026-04-09 17:16:25 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 4.2 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H

Problem Types: CWE-1333 | CWE-1333 CWE-1333: Inefficient Regular Expression Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.2MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H
3.1CNADECLARED4.2MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
High
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Nearform Fast-jwt affected >= 5.0.0, < 6.2.1 Not specified

References

ReferenceSourceLinkTags
github.com/nearform/fast-jwt/pull/595 [email protected] github.com
github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/nearform/fast-jwt/releases/tag/v6.2.1 [email protected] github.com
github.com/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5... [email protected] github.com
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