Auth bypass in Duende Identityserver4
CVE-2026-4349
A vulnerability was determined in Duende IdentityServer4 up to 4.1.2. The affected element is an unknown function of the file /connect/authorize of the component Token Renewal Endpoint. This manipulation of the argument id_token_hint causes improper authentication. It is possible to initiate the attack remotely. The attack is considered to have high complexity. The exploitability is described as difficult. This vulnerability only affects products that are no longer supported by the maintainer.
Vulnerability class: Broken Authentication
EPSS: 0.004 (33.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.6 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L.
Affected products
- Duende Identityserver4 — versions 4.1.0, 4.1.1, 4.1.2
Weakness classification (CWE)
References
- cna@vuldb.com (technical-description, vdb-entry)
- cna@vuldb.com (signature, permissions-required)
- cna@vuldb.com (third-party-advisory)
Frequently asked questions
- What is CVE-2026-4349?
- CVE-2026-4349 is a medium-severity vulnerability in Duende Identityserver4, classified under Improper Authentication. CVSS score: 5.6/10. Published 2026-03-17.
- How severe is CVE-2026-4349?
- Medium severity. CVSS v3 base score is 5.6 out of 10.