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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-107721: 0.34% estimated exploitation activity in the next 30 days; percentile 27.71 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: Infinity passes (it's a number, not less than 0, truthy). src/verifier.js:583-602 — clockTolerance flows into the date-claim validators: src/verifier.js:198-205 — applies modifier additively, producing always-pass comparisons: Empirical PoC Verified against fast-jwt@HEAD on 2026-06-03 (commit pulled today). Cache side-effect The verifier's LRU cache uses clockTolerance to compute the cache entry's expiry window: src/verifier.js:121-134: With clockTolerance: Infinity, cache entries are stored with min=-Infinity,…

Published by the source

8 Oct 2026, 22:02 UTC

Last modified by the source

8 Oct 2026, 22:15 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-687g-22h4-j4w4

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-687g-22h4-j4w4

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-687g-22h4-j4w4

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# Patch Next advisory brief: CVE-2026-107721

Advisory: fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)
IDs: CVE-2026-107721, GHSA-687g-22h4-j4w4
Record: https://patchnext.com/advisories/cve-2026-107721 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fast-jwt 6.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fast-jwt: affected <= 6.2.4; fixed in 6.3.0

## Suggested inspection (read-only)
- `npm ls fast-jwt --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fast-jwt.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-687g-22h4-j4w4 (GitHub-reviewed advisory GHSA-687g-22h4-j4w4 lists affected ranges: npm fast-jwt >=0 <=6.2.4)
- Verified: https://osv.dev/vulnerability/GHSA-687g-22h4-j4w4 (OSV record GHSA-687g-22h4-j4w4 lists affected ranges: npm fast-jwt >=0 <6.3.0 (fixed))

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