{"id":"CVE-2026-107720","sourceIdentifier":"security-advisories@github.com","published":"2026-10-08T22:17:28.090","lastModified":"2026-10-09T15:17:08.947","vulnStatus":"Deferred","cveTags":[],"descriptions":[{"lang":"en","value":"fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"nearform","product":"fast-jwt","versions":[{"version":"< 6.3.1","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","baseScore":7.4,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"NONE"},"exploitabilityScore":2.2,"impactScore":5.2}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-10-09T14:31:56.862139Z","id":"CVE-2026-107720","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-20"},{"lang":"en","value":"CWE-347"}]}],"references":[{"url":"https://github.com/nearform/fast-jwt/commit/e22a151e83bf6d5e54e281216982d204d5665534","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/pull/649","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/releases/tag/v6.3.1","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}]}