Duende IdentityServer4 up to 4.1.2 Token Renewal Endpoint /connect/authorize id_token_hint improper authentication

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.
CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.6$0-$5k0.00

Summaryinfo

A vulnerability categorized as critical has been discovered in Duende IdentityServer4 up to 4.1.2. 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 only affects products that are no longer supported by the maintainer. This vulnerability is referenced as CVE-2026-4349. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Duende IdentityServer4 up to 4.1.2. 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 03/25/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

Name

Version

Support

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

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: 🔍

CNA Base Score: 5.6
CNA Vector: 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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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

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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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
03/25/2026 +8 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
Updated: 03/25/2026 13:10
Changes: 03/17/2026 18:08 (53), 03/21/2026 22:36 (30), 03/25/2026 12:00 (4), 03/25/2026 13:10 (1)
Complete: 🔍
Submitter: Edcarlos
Cache ID: 216::103

Submitinfo

Accepted

  • Submit #772071: DuendeSoftware Identity Server 4 Authentication Bypass Issues (by Edcarlos)

Once again VulDB remains the best source for vulnerability data.

Discussion

 damian-duende (+0)
2 months ago
There is no such thing as "Duende IdentityServer 4".

There is IdentityServer4 https://github.com/DuendeArchive/IdentityServer4 which is deprecated and archived.

Duende IdentityServer is a separate product that started at version 5 and is currently at 7.4.x https://github.com/duendeSoftware/products/

This report should be updated to reflect which *actual* software was tested.
 VulDB Community Team2 months ago
Thank you, we have just updated the entry.
 damian-duende (+0)
2 months ago
To add:

> The vendor was contacted early about this disclosure but did not respond in any way.

This is a falsehood. We have a clear communication procedure https://github.com/duendeSoftware/products/?tab=security-ov-file#reporting-security-issues .

This report should be rescinded pending corrections in the accuracy of the reporting.
 VulDB Community Team2 months ago
The original GitHub repo does not mention any mail address. Therefore, a notification happened on 2026-03-07 via email to the address that was mentioned at https://github.com/DuendeSoftware - Until today we have not received any reply to that inquiry.

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