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Description

fast-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.

PUBLISHED Reserved 2026-03-31 | Published 2026-04-09 | Updated 2026-04-13 | Assigner GitHub_M




MEDIUM: 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Problem types

CWE-697: Incorrect Comparison

CWE-440: Expected Behavior Violation

Product status

< 6.2.1
affected

References

github.com/...st-jwt/security/advisories/GHSA-3j8v-cgw4-2g6q

github.com/nearform/fast-jwt/pull/593

github.com/...ommit/18d25904e4617e8753526d1b3ab5a2cccdea726a

github.com/nearform/fast-jwt/releases/tag/v6.2.1

cve.org (CVE-2026-35040)

nvd.nist.gov (CVE-2026-35040)

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