CVE-2026-35040
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.
Does this matter?
Lower severity and a low EPSS score (0.38%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- EPSS
- 0.38% probability · 32th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-440, CWE-697
- Affected
- nearform/fast-jwt
- Source
- security-advisories@github.com
References
- https://github.com/nearform/fast-jwt/commit/18d25904e4617e8753526d1b3ab5a2cccdea726aPatch
- https://github.com/nearform/fast-jwt/pull/593Issue Tracking, Patch
- https://github.com/nearform/fast-jwt/releases/tag/v6.2.1Product, Release Notes
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-3j8v-cgw4-2g6qExploit, Mitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.