CVE-2026-107721
published 2026-10-08CVE-2026-107721: fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts Infinity for clockTolerance because its option…
PriorityP433medium5.9CVSS 3.1
AVNACHPRHUINSUCHIHAN
EPSS
0.33%
25.6th percentile
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.
Affected
2 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| nearform | fast-jwt | < 6.3.0 | 6.3.0 |
| nearform | fast-jwt | >= 0 < 6.3.0 | 6.3.0 |
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VulDB
nearform fast-jwt up to 6.2.x Verifier createVerifier clockTolerance comparison (EUVD-2026-95345)
vuldb·2026-10-09·CVSS 5.9
CVE-2026-107721 [MEDIUM] nearform fast-jwt up to 6.2.x Verifier createVerifier clockTolerance comparison (EUVD-2026-95345)
A vulnerability described as problematic has been identified in nearform fast-jwt up to 6.2.x. The affected element is the function createVerifier of the component Verifier. Executing a manipulation of the argument clockTolerance can lead to incorrect comparison.
This vulnerability is registered as CVE-2026-107721. It is possible to launch the attack remotely. No exploit is available.
Upgrading the affected component is recommended.
GHSA
fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)
ghsa·2026-10-08
CVE-2026-107721 [MEDIUM] CWE-613 fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)
fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)
## Summary
`createVerifier({ clockTolerance: Infinity })` silently bypasses both `exp` (expiry) AND `nbf` (not-before) validation. Any expired or not-yet-active token is accepted as valid. The same primitive also corrupts the verifier's internal cache so cached entries inherit infinite validity — they remain valid past a later developer-removed Infinity config until LRU eviction.
## Vulnerable code
`src/verifier.js:531-533` — option validation only rejects negative values, not Infinity:
```js
if (clockTolerance && (typeof clockTolerance !== 'number' || clockTolerance = adjusted : now <= adjusted // → always true
...
}
```
## Empirical PoC
```js
const { createSigner, c
No detection rules found.
No public exploits indexed.
No writeups or analysis indexed.
2026-10-08
Published