fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts Infinity for clockTolerance because its option validation checks type and negativity but not finiteness. In validateClaimDateValue, infinite positive and negative modifiers make exp and nbf comparisons always pass, allowing expired or not-yet-active tokens to be accepted. The verifier cache also derives infinite bounds, so entries created under this configuration can remain valid until eviction. Exploitation requires an application administrator or equivalent configuration path to set clockTolerance to Infinity. This issue is fixed in version 6.3.0.

Source published

8 Oct 2026 21:45:57 UTC

Source modified

9 Oct 2026 15:13:11 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N