PT-2026-41315 · Benmcollins · Libjwt

Published

2026-05-15

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Updated

2026-05-15

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CVE-2026-44699

CVSS v4.0

9.1

Critical

VectorAV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
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.

Exploit

Fix

Improper Verification of Cryptographic Signature

Use of a Broken Cryptographic Algorithm

Weakness Enumeration

CWE-347CWE-327

Related Identifiers

CVE-2026-44699

Affected Products

Libjwt