EUVD-2026-30560CVSS VectorNVD
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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4DescriptionNVD
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.
AnalysisAI
Algorithm confusion in LibJWT 3.0.0 through 3.3.2 allows authentication bypass when RSA JWKs lack the 'alg' parameter. The OpenSSL backend incorrectly processes HMAC verification with a zero-length key when an RSA key without 'alg' is used to verify HS256/HS384/HS512 tokens, enabling attackers to forge valid JWTs without knowing any secret. …
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RemediationAI
Within 24 hours: Inventory all applications and services using LibJWT 3.0.0-3.3.2 and assess exposure in authentication-critical paths. Within 7 days: Apply vendor-released patch to upgrade LibJWT to version 3.3.3 or later across all production, staging, and development environments. …
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