{"id":"CVE-2026-44351","sourceIdentifier":"security-advisories@github.com","published":"2026-05-13T20:16:22.860","lastModified":"2026-10-26T14:10:00.130","vulnStatus":"Deferred","cveTags":[],"descriptions":[{"lang":"en","value":"fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4."},{"lang":"es","value":"fast-jwt proporciona una implementación rápida de JSON Web Token (JWT). Antes de la versión 6.2.4, una vulnerabilidad crítica de omisión de autenticación en el flujo asíncrono de resolución de claves de fast-jwt permite a cualquier atacante no autenticado forjar JWTs arbitrarios que son aceptados como auténticos. Cuando el resolvedor de claves de la aplicación devuelve una cadena vacía (’’), por ejemplo a través del fallback común estilo JWKS keys[decoded.header.kid] || ’’, fast-jwt lo convierte en un Buffer de longitud cero, lo entrega a crypto.createSecretKey, deriva allowedAlgorithms = [’HS256’,’HS384’,’HS512’] de él, y luego verifica la firma del token contra un HMAC de clave vacía. El atacante simplemente calcula HMAC-SHA256(key=’’, input=’${header}.${payload}’), lo cual Node acepta sin quejas - y el verificador devuelve la carga útil elegida por el atacante (sub, admin, scopes, etc.) como auténtica. Esta vulnerabilidad se corrige en la versión 6.2.4."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"nearform","product":"fast-jwt","versions":[{"version":"< 6.2.4","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","baseScore":9.1,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"NONE"},"exploitabilityScore":3.9,"impactScore":5.2}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-14T18:13:28.571023Z","id":"CVE-2026-44351","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-287"},{"lang":"en","value":"CWE-326"},{"lang":"en","value":"CWE-1391"}]}],"references":[{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}]}