CVE-2026-44351— fast-jwt: Empty HMAC secret accepted via async key resolver - JWT auth bypass

fast-jwt: Empty HMAC secret accepted via async key resolver - JWT auth bypass

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

认证机制不恰当

fast-jwt 授权问题漏洞

fast-jwt是Nearform开源的一个 JSON Web Token 实现。 fast-jwt 6.2.4之前版本存在授权问题漏洞，该漏洞源于异步密钥解析流程中的关键身份验证绕过漏洞，允许未经身份验证的攻击者伪造任意JWT令牌。

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