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.

Project Subscriptions

Vendors Products
Benmcollins Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Fri, 15 May 2026 18:15:00 +0000

Type Values Removed Values Added
First Time appeared Benmcollins
Benmcollins libjwt
Vendors & Products Benmcollins
Benmcollins libjwt
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Fri, 15 May 2026 16:45:00 +0000

Type Values Removed Values Added
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.
Title LibJWT: Algorithm confusion allows JWT forgery with RSA JWK as empty-key HMAC
Weaknesses CWE-327
CWE-347
References
Metrics cvssV4_0

{'score': 9.1, 'vector': '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'}


Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-15T18:04:58.082Z

Reserved: 2026-05-07T17:07:09.316Z

Link: CVE-2026-44699

cve-icon Vulnrichment

Updated: 2026-05-15T18:01:05.454Z

cve-icon NVD

Status : Received

Published: 2026-05-15T17:16:47.783

Modified: 2026-05-15T19:17:00.467

Link: CVE-2026-44699

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-15T18:00:05Z

Weaknesses