fast-jwt: Stateful RegExp (/g or /y) causes non-deterministic allowed-claim validation (logical DoS)

MITRE NVD CVE.ORG JSON API Print: PDF PDF

Summary

CVECVE-2026-35040
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-09 16:16:27 UTC
Updated2026-04-17 20:10:05 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

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

EPSS: 0.000720000 probability, percentile 0.219810000 (date 2026-04-17)

Problem Types: CWE-440 | CWE-697 | CWE-697 CWE-697: Incorrect Comparison | CWE-440 CWE-440: Expected Behavior Violation

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

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

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Nearform Fast-jwt All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Nearform Fast-jwt affected < 6.2.1 Not specified

References

ReferenceSourceLinkTags
github.com/nearform/fast-jwt/commit/18d25904e4617e8753526d1b3ab5a2cccdea... [email protected] github.com Patch
github.com/nearform/fast-jwt/security/advisories/GHSA-3j8v-cgw4-2g6q [email protected] github.com Exploit, Mitigation, Vendor Advisory
github.com/nearform/fast-jwt/releases/tag/v6.2.1 [email protected] github.com Product, Release Notes
github.com/nearform/fast-jwt/pull/593 [email protected] github.com Issue Tracking, Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
© CVE.report 2026 |

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report