CVE-2026-107721 fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)
Attackers can bypass JWT expiration and not-before checks if clockTolerance is set to Infinity, allowing use of invalid tokens.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-107721?
CVE-2026-107721 is a medium-severity vulnerability in nearform fast-jwt, published on 8 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-107721?
2 open source packages ship an affected version, including fast-jwt.
| Package | Affected | Fixed in |
|---|---|---|
fast-jwt npm | All versions | 6.3.0 |
fast-jwt npm | All versions | 6.3.0 |
How do I fix CVE-2026-107721?
Upgrade fast-jwt to 6.3.0 or later.
Is CVE-2026-107721 being exploited?
There is no known exploitation of CVE-2026-107721 in the wild and no public exploit code.
Sources
Also known as GHSA-687g-22h4-j4w4.