CVE-2026-44699

CRITICAL EPSS 11.1%
Published May 15, 20261mo ago · Modified Jun 17, 20261w ago
9.1 CVSS 4.0
Critical
Find Similar
Published May 15, 2026 1mo ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
9.1
Exploitability
—
Impact
—
Vector string
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
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
11.1% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 2

CWE-327
CWE-347

References 1

  • github.com https://github.com/benmcollins/libjwt/security/advisories/GHSA-q843-6q5f-w55g

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.