CVE-2026-44699 Details
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.
A vulnerability in LibJWT versions 3.0.0 through 3.3.2 allows for the forgery of JSON Web Tokens (JWTs) by exploiting algorithm confusion in the handling of RSA JSON Web Key (JWK) verification. When an RSA JWK is provided without an 'alg' parameter, LibJWT's OpenSSL backend mistakenly uses a zero-length key for HMAC verification of HS256, HS384, or HS512 tokens. This flaw enables an attacker to create a valid JWT without knowledge of any secret or RSA private key. The issue arises in applications that load RSA keys from JWK Sets (JWKS) where the 'alg' is omitted—a common scenario in real-world deployments—and then select the verification algorithm based on the JWT header, such as through a key ID lookup callback.
Users can upgrade to LibJWT version 3.3.3, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 15, 2026CISA-ADP
Assessed May 15, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/benmcollins/libjwt/security/advisories/GHSA-q843-6q5f-w55g | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/benmcollins/libjwt/security/advisories/GHSA-q843-6q5f-w55g | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-327 | Use of a Broken or Risky Cryptographic Algorithm | [email protected] |
| CWE-347 | Improper Verification of Cryptographic Signature | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| LibJWT | All versions |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 15, 2026 | CVE Modified | CISA-ADP |
| May 15, 2026 | New CVE Received | [email protected] |