EUVD-2026-12659CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
Lifecycle Timeline
3Description
A vulnerability was determined in Duende IdentityServer 4. 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. The vendor was contacted early about this disclosure but did not respond in any way.
Analysis
A improper authentication vulnerability exists in Duende IdentityServer 4 affecting the Token Renewal Endpoint at /connect/authorize, where manipulation of the id_token_hint parameter can bypass authentication controls. This vulnerability affects Duende IdentityServer 4 across all versions, allowing remote attackers without credentials to gain unauthorized access with high complexity exploitation requirements. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Audit authentication configurations.
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