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.

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

Published 2026-03-17 · last modified 2026-06-17.

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.

EPSS exploit prediction

EPSS: 0.005 (43.2th percentile), scored 2026-10-05.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 43.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001

Affected products

Duende Identityserver4 — versions 4.1.0, 4.1.1, 4.1.2

Weakness classification (CWE)

CWE-287 — Improper Authentication

References

vuldb.com/ (technical-description, vdb-entry)
vuldb.com/ (signature, permissions-required)
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.