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

fast-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.

Source published

9 Apr 2026 14:55:22 UTC

Source modified

9 Apr 2026 16:15:25 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

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CVSS 3.1 · 4.2 CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H