CVE-2026-35040

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.

The following products are affected by CVE-2026-35040 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-35040.

URL	Resource
https://github.com/nearform/fast-jwt/commit/18d25904e4617e8753526d1b3ab5a2cccdea726a
https://github.com/nearform/fast-jwt/pull/593
https://github.com/nearform/fast-jwt/releases/tag/v6.2.1
https://github.com/nearform/fast-jwt/security/advisories/GHSA-3j8v-cgw4-2g6q