CVE-2026-4349 | Duende IdentityServer 4 Token Renewal Endpoint /connect/authorize id_token_hint improper authentication

VDB-351380 · CVE-2026-4349 · GCVE-100-351380 DUENDE IDENTITYSERVER 4 TOKEN RENEWAL ENDPOINT /CONNECT/AUTHORIZE ID_TOKEN_HINT IMPROPER AUTHENTICATION HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 5.6 $0-$5k 2.05+ Summaryinfo A vulnerability categorized as critical has been discovered in Duende IdentityServer 4. The impacted element is an unknown function of the file /connect/authorize of the component Token Renewal Endpoint. Such manipulation of the argument id_token_hint leads to improper authentication. This vulnerability is referenced as CVE-2026-4349. It is possible to launch the attack remotely. No exploit is available. The vendor was contacted early about this disclosure but did not respond in any way. Detailsinfo A vulnerability, which was classified as critical, has been found in Duende IdentityServer 4. Affected by this issue is an unknown functionality of the file /connect/authorize of the component Token Renewal Endpoint. The manipulation of the argument id_token_hint with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is confidentiality, integrity, and availability. This vulnerability is handled as CVE-2026-4349. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 03/17/2026). The vendor was contacted early about this disclosure but did not respond in any way. There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product. Productinfo Vendor Duende Name IdentityServer Version 4 CPE 2.3info 🔒 CPE 2.2info 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 5.6 VulDB Meta Temp Score: 5.6 VulDB Base Score: 5.6 VulDB Temp Score: 5.6 VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Improper authentication CWE: CWE-287 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: no mitigation known Status: 🔍 0-Day Time: 🔒 Timelineinfo 03/17/2026 Advisory disclosed 03/17/2026 +0 days VulDB entry created 03/17/2026 +0 days VulDB entry last update Sourcesinfo Status: Not defined CVE: CVE-2026-4349 (🔒) GCVE (CVE): GCVE-0-2026-4349 GCVE (VulDB): GCVE-100-351380 Entryinfo Created: 03/17/2026 18:08 Changes: 03/17/2026 18:08 (53) Complete: 🔍 Submitter: Edcarlos Cache ID: 99:F79:101 Submitinfo Accepted Submit #772071: DuendeSoftware Identity Server 4 Authentication Bypass Issues (by Edcarlos) Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸