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

{
  "id": "a301fe5e6afbfbddb59075a75ffcae766f34608e13ac04f07998dbab2a60c939",
  "url": "https://osv.dev/vulnerability/GHSA-687g-22h4-j4w4",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)",
    "summary": "## 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 < 0)) { throw new TokenError(TokenError.codes.invalidOption, 'The clockTolerance option must be a positive number.') } ``` `Infinity` passes (it's a number, not less than 0, truthy). `src/verifier.js:583-602` — clockTolerance flows into the date-claim validators: ```js if (!ignoreNotBefore) { validators.push({ ..., modifier: -clockTolerance }) // → -Infinity } if (!ignoreExpiration) { validators.push({ ..., modifier: +clockTolerance }) // → Infinity } ``` `src/verifier.js:198-205` — applies modifier additively, producing always-pass comparisons: ```js function validateClaimDateValue(value, modifier, now, greater, errorCode, errorVerb) { const adjusted = value * 1000 + (modifier || 0) // → ±Infinity const valid = greater ? now >= adjusted : now <= adjusted // → always true ... } ``` ## Empirical PoC ```js const { createSigner, createVerifier } = require('fast-jwt') const secret = 'test-secret-with-enough-length-to",
    "evidence": "osv:GHSA-687g-22h4-j4w4",
    "products": [
      {
        "name": {
          "value": "fast-jwt",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.3.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-687g-22h4-j4w4",
      "aliases": [
        "CVE-2026-107721",
        "GHSA-687g-22h4-j4w4"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "6.3.0"
                }
              ]
            }
          ],
          "package": {
            "name": "fast-jwt",
            "purl": "pkg:npm/fast-jwt",
            "ecosystem": "npm"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-687g-22h4-j4w4/GHSA-687g-22h4-j4w4.json",
            "last_known_affected_version_range": "<= 6.2.4"
          }
        }
      ],
      "modified": "2026-10-08T22:15:05.893519907Z",
      "provider": "osv",
      "references": [
        "https://github.com/nearform/fast-jwt/security/advisories/GHSA-687g-22h4-j4w4",
        "https://github.com/nearform/fast-jwt/commit/c0fb5b88b4c88ff2bdd194ca2c713599ad9e38b6",
        "https://github.com/nearform/fast-jwt",
        "https://github.com/nearform/fast-jwt/releases/tag/v6.3.0"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-613",
          "CWE-682"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-08T22:02:02Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-107721",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 104808,
  "published_at": "2026-10-08T22:02:02+00:00"
}