Insufficient Session Expiration Affecting fast-jwt package, versions <6.3.4
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Start learning- Snyk IDSNYK-JS-FASTJWT-20825051
- published11 Oct 2026
- disclosed8 Oct 2026
- creditSomnath Das, Eurico Nicacio, BlueN0r, kagebunsher
Introduced: 8 Oct 2026
NewCVE-2026-107719 (opens in a new tab)How to fix?
Upgrade fast-jwt to version 6.3.4 or higher.
Overview
fast-jwt is a Fast JSON Web Token implementation
Affected versions of this package are vulnerable to Insufficient Session Expiration via the verifier cache in src/verifier.js, where the cacheSet function only derived exp and nbf bounds from a token's payload when the iat claim was also present. An attacker can present a token that lacks iat to bypass expiration enforcement: the token is cached until the cacheTTL bound rather than until exp, and the nbf lower bound is also not applied, allowing an expired or not-yet-valid token to be accepted on subsequent cached lookups.
Note: This is only exploitable when the verifier cache is enabled and the presented JWT omits the iat claim.