CVE-2026-44699— LibJWT: Algorithm confusion allows JWT forgery with RSA JWK as empty-key HMAC
Possible ATT&CK Techniques 1AI
T1190 · Exploit Public-Facing ApplicationAffected Version Matrix 1
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| benmcollins | libjwt | >= 3.0.0, < 3.3.3 | affected |
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I. Basic Information for CVE-2026-44699
Vulnerability Information
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Vulnerability Title
LibJWT: Algorithm confusion allows JWT forgery with RSA JWK as empty-key HMAC
Source: NVD (National Vulnerability Database)
Vulnerability Description
LibJWT is a C JSON Web Token Library. From 3.0.0 to 3.3.2, libjwt accepts an RSA JWK that does not contain an alg parameter as the verification key for an HS256/HS384/HS512 token. In the OpenSSL backend, this causes HMAC verification to run with a zero-length key, so an attacker can forge a valid JWT without knowing any secret or RSA private key. This is an algorithm-confusion authentication bypass. It affects applications that load RSA keys from JWKS where alg is omitted, which is valid JWK syntax and common in real deployments, and then choose the verification algorithm from the JWT header, for example in a kid lookup callback. This vulnerability is fixed in 3.3.3.
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
使用已被攻破或存在风险的密码学算法
Source: NVD (National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| benmcollins | libjwt | >= 3.0.0, < 3.3.3 | - |
II. Public POCs for CVE-2026-44699
| # | POC Description | Source Link | Shenlong Link |
|---|
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IV. Related Vulnerabilities
Same weakness: CWE-327
V. Comments for CVE-2026-44699
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