Authentication bypass via empty-key HMAC verification
Published May 15, 2026 · Updated May 15, 2026
Algorithm confusion in LibJWT 3.0.0 through 3.3.2 allows remote attackers to forge JWTs and bypass application authentication. __setkey_check() accepts an RSA JWK lacking alg for an HMAC algorithm, and the OpenSSL path reads the union's zero-length octet key while treating RSA modulus bits as HMAC strength. Exploitation requires an application to load such an RSA key from JWKS and let the token header select HS256, HS384, or HS512; forged claims can grant unauthorized identity or privileges.
Summary
What happened
Algorithm confusion in LibJWT 3.0.0 through 3.3.2 allows remote attackers to forge JWTs and bypass application authentication. __setkey_check() accepts an RSA JWK lacking alg for an HMAC algorithm, and the OpenSSL path reads the union's zero-length octet key while treating RSA modulus bits as HMAC strength. Exploitation requires an application to load such an RSA key from JWKS and let the token header select HS256, HS384, or HS512; forged claims can grant unauthorized identity or privileges.
The record
- CVE
- CVE-2026-44699
- Published
- May 15, 2026
- Updated
- May 15, 2026
- Vendor
- LibJWT
- Product
- LibJWT
- Classifications
- CWE-347, CWE-327, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 15, 2026CVE publishedPublication date reported by the CVE source.
- May 15, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 3.0.0, < 3.3.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Upstream empty-key HMAC JWT forgery PoCproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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