fast-jwt: Empty HMAC secret accepted via async key resolver – JWT auth bypass_CVE-2026-44351

{
    "lastseen": "",
    "description": "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 \u2014 and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4.",
    "published": "2026-05-13T19:12:33.347Z",
    "modified": "2026-05-13T19:12:33.347Z",
    "type": "cve",
    "title": "fast-jwt: Empty HMAC secret accepted via async key resolver - JWT auth bypass",
    "source": "GitHub_M",
    "references": "https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc",
    "id": "CVE-2026-44351",
    "bulletinFamily": "",
    "cwe": [
        "CWE-287",
        "CWE-326",
        "CWE-1391"
    ],
    "cvelist": null,
    "sourceData": "nearform fast-jwt < 6.2.4",
    "sourceHref": "",
    "cvss": {
        "score": 9.1,
        "severity": "CRITICAL",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "fast-jwt",
    "version": "< 6.2.4",
    "vendor": "nearform",
    "ai_description": "Authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows unauthenticated attackers to forge arbitrary JWTs",
    "ai_severity": "Critical",
    "ai_vendor": "nearform",
    "ai_product": "fast-jwt",
    "ai_version": "< 6.2.4",
    "ai_score": 9.1
}