CVE-2026-4349Network attack vector

Authentication bypass via manipulated id_token_hint

Published Mar 17, 2026 · Updated Mar 17, 2026

Improper authentication in Duende IdentityServer4 4.1.2 and earlier allows remote attackers to bypass authentication via id_token_hint. An undisclosed function at /connect/authorize improperly processes a manipulated id_token_hint during token renewal; no vendor mechanism details are public. The request needs no credentials but has high attack complexity; the record does not identify the resulting account or session capability.

CVSS severity6.3
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Duende IdentityServer4 4.1.2 and earlier allows remote attackers to bypass authentication via id_token_hint. An undisclosed function at /connect/authorize improperly processes a manipulated id_token_hint during token renewal; no vendor mechanism details are public. The request needs no credentials but has high attack complexity; the record does not identify the resulting account or session capability.

The record

CVE
CVE-2026-4349
Published
Mar 17, 2026
Updated
Mar 17, 2026
Vendor
Duende Software
Product
Duende IdentityServer
Classifications
CWE-287, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 17, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Duende Software · Duende IdentityServerversion=4

Published CVSS scores

6.3VulDBCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
5.6VulDBCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
5.1VulDBAV:N/AC:H/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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