{"id":"CVE-2026-107724","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-107724","generatedAt":"2026-10-28T03:59:23.531Z","title":"If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts.","description":"fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because src/crypto.js performDetectPublicKeyAlgorithms treats non-PEM strings as symmetric key material. If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts. Serialization ordering or whitespace differences can prevent exploitation, and applications using supported PEM keys with an asymmetric-only algorithm allowlist are not affected. This issue is fixed in version 6.3.0.","published":"2026-10-08T22:17:29.000Z","lastModified":"2026-10-09T16:17:24.000Z","status":"Deferred","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":7.4,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"},"cwe":["CWE-347"],"affected":[],"epss":{"score":0.00282,"percentile":0.20545,"date":"2026-10-27","history":[{"date":"2026-10-09","score":0.00222,"percentile":0.11709}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.28%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-08T22:17:29.000Z","detail":{"score":"7.4","severity":"HIGH","publishedAt":"2026-10-08T22:17:28.800Z"},"summary":"New CVE, high severity (CVSS 7.4)."}],"references":[{"url":"https://github.com/nearform/fast-jwt/commit/10f9591349199ed2ab9fa1748ce92cdca697f6cf","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/pull/636","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/releases/tag/v6.3.0","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-g3jj-5cmm-3hxx","source":"security-advisories@github.com"},{"url":"https://github.com/nearform/fast-jwt/security/advisories/GHSA-g3jj-5cmm-3hxx","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-107724","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}