CVE-2026-44699 (GCVE-0-2026-44699)

Vulnerability from cvelistv5 – Published: 2026-05-15 16:08 – Updated: 2026-05-15 18:04
VLAI
Title
LibJWT: Algorithm confusion allows JWT forgery with RSA JWK as empty-key HMAC
Summary
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.
Severity
9.1 (Critical)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SSVC
Exploitation: poc Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-05-15 18:00 UTC
CWE
  • CWE-327 - Use of a Broken or Risky Cryptographic Algorithm
  • CWE-347 - Improper Verification of Cryptographic Signature
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7771 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
benmcollins libjwt Affected: >= 3.0.0, < 3.3.3
guessed Create a notification for this product.
Show details on NVD website
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