dbcve.org
Improper AuthenticationWeakness · CWE-287

CVE-2026-4349

MEDIUM · 5.6 CVSS v3.1 Published 2026-03-17
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
65/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Improper authentication vulnerability in Duende IdentityServer4's /connect/authorize endpoint where manipulation of the id_token_hint parameter during token renewal allows authentication bypass. The attack is difficult to exploit with high complexity and only affects end-of-life versions.

MitigationSince this affects only unsupported product versions (EOL), the primary remediation is migrating to a currently supported IdentityServer version or alternative identity solution. If immediate migration is not feasible, implement additional compensating controls such as strict network segmentation and enhanced monitoring on the authorization endpoint.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if Duende IdentityServer4 is in use
    Review application dependencies, deployed assemblies, or running processes for IdentityServer4 components. Check NuGet packages or application configuration files for Duende.IdentityServer references.
    Affected if The environment contains Duende IdentityServer4 or its predecessors (previously known as IdentityServer4 before rebranding)
  2. Determine the installed IdentityServer4 version
    Check the deployed DLL/assembly version, NuGet package reference in .csproj or packages.config, or the version reported by the running service if available via diagnostic endpoints.
    Affected if The version is an end-of-life (unsupported) release - compare against vendor's support lifecycle documentation for IdentityServer4 versions
  3. Verify exposure of the /connect/authorize endpoint
    Review application routing configuration, proxy rules, or network accessibility to confirm the /connect/authorize endpoint is externally or internally accessible.
    Affected if The /connect/authorize endpoint is reachable from any network context where token renewal would occur
  4. Confirm id_token_hint parameter usage in token renewal flows
    Examine OpenID Connect configuration, authorization request logs, or application code to determine if id_token_hint is used during token renewal or silent re-authentication scenarios.
    Affected if The application uses id_token_hint during token renewal, which is common in silent token refresh patterns

The environment is likely affected if it runs an end-of-life version of Duende IdentityServer4 with the /connect/authorize endpoint exposed and id_token_hint used in token renewal flows, though exploitation requires high complexity.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Since this affects only unsupported product versions (EOL), the primary remediation is migrating to a currently supported IdentityServer version or alternative identity solution. If immediate migration is not feasible, implement additional compensating controls such as strict network segmentation and enhanced monitoring on the authorization endpoint.

Have this fixed Scoped from the published advisory
  • Consultation8.0 h
  • Implementation24.0 h
  • Testing12.0 h
  • Review / QA6.0 h
50.0 hours of engineering $8,800
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $14,080.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-4349 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-4349 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data