CVE-2026-4349: Duende IDENTITYSERVER4

Medium severity, CVSS 5.6. EPSS: 0.5% chance of exploitation in the next 30 days.

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.

Affected products

• Duende IDENTITYSERVER4: version 4.1.0 only; version 4.1.1 only; version 4.1.2 only

Published 2026-03-17. Last modified 2026-06-17.