dbcve.org
Information ExposureWeakness · CWE-200

CVE-2026-40166

HIGH · 7.1 CVSS v4.0 Published 2026-05-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
77/100
Remediation priority · High
Remotely reachable 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
authentik is an open-source identity provider. In versions prior to 2025.12.5 and 2026.2.0-rc1 through 2026.2.2, authenticated non-admin users with at least one OAuth2 access token can retrieve the client_secret of confidential OAuth2 providers they have previously authenticated against, exposing sensitive information to users without the correct permissions. This logic is GET /api/v3/oauth2/access_tokens/. The API response includes a nested provider object containing client_id and client_secret for providers configured with client_type: confidential, which should not be accessible to low-privilege users. This issue has been fixed in versions 2025.12.5 and 2026.2.3.

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 · high confidence

Non-admin authenticated users with OAuth2 access tokens can retrieve client_secrets of confidential OAuth2 providers via the GET /api/v3/oauth2/access_tokens/ endpoint. The API response incorrectly includes a nested provider object containing both client_id and client_secret for confidential client types, exposing sensitive credentials to unauthorized users.

MitigationUpgrade authentik to version 2025.12.5 or 2026.2.3 which contains the fix. Additionally, rotate any potentially exposed OAuth2 client_secrets as a precaution.

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
Low
Privileges
Low
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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 installed authentik version
    Run 'ak version' or check the Docker container/image tag or Helm chart version deployed in your environment. Compare against fixed versions 2025.12.5 and 2026.2.3.
    Affected if The installed version is earlier than 2025.12.5 or between 2026.0.0 and 2026.2.2 (not inclusive).
  2. Confirm OAuth2 providers are configured
    Navigate to the authentik admin UI, go to the OAuth2 provider section, or query the /api/v3/oauth2/provider/ endpoint using an authenticated session to list configured providers.
    Affected if Any OAuth2 providers are defined in the system, particularly confidential providers that use client_id and client_secret.
  3. Verify non-admin user access to the token endpoint
    Using a non-admin user account (not assigned admin privileges), authenticate and make a GET request to /api/v3/oauth2/access_tokens/. Check the HTTP response status and content.
    Affected if The endpoint returns a 200 OK response with token data when accessed by a non-admin user, rather than returning 403 Forbidden.
  4. Check for credential exposure in API response
    Examine the JSON response from /api/v3/oauth2/access_tokens/ for any fields containing 'client_id' or 'client_secret' values that should be restricted.
    Affected if The response includes actual client_secret values in plain text for any OAuth2 provider object.

You are affected if your authentik version is before 2025.12.5 or between 2026.0.0 and 2026.2.2, and non-admin users can retrieve OAuth2 provider credentials from the access_tokens endpoint.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade authentik to version 2025.12.5 or 2026.2.3 which contains the fix. Additionally, rotate any potentially exposed OAuth2 client_secrets as a precaution.

Recommended fix High confidence

2025.12.5 or 2026.2.3 (or later stable release)

  1. Identify the currently running version of authentik by checking the system or deployment configuration
  2. If running a version prior to 2025.12.5, upgrade to version 2025.12.5 or later
  3. If running version 2026.2.0-rc1 through 2026.2.2, upgrade to version 2026.2.3 or later
  4. After upgrading, verify that non-admin users can no longer access client_secret values via the /api/v3/oauth2/access_tokens/ endpoint
  5. Review OAuth2 provider configurations to ensure client_type settings are appropriate for your security requirements
Caveat Review release notes for any breaking changes between your current version and the target upgrade version before deploying

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2026-40166 in production — separate from our analysis above.

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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