CVE-2026-40166
Published: 22 May 2026
Summary
CVE-2026-40166 is a high-severity Exposure of Sensitive Information to an Unauthorized Actor (CWE-200) vulnerability. Its CVSS base score is 7.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Unsecured Credentials (T1552); ranked at the 29.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-31490
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability enables unauthorized retrieval of OAuth2 client secrets (application credentials) via improper authorization on an API endpoint.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Defining permitted attribute values and auditing modifications reduces the chance of incorrect authorization outcomes due to tampered or missing labels.
Ensures authorization decisions for external system use are correctly implemented and enforced.
It assists users in evaluating and applying correct authorization decisions when sharing information with external partners.
Session auditing enables detection of unauthorized exposure or access to sensitive information during user activities.
Drives review and correction of flawed authorization logic applied to organizational data.
Annual reviews and proposal scrutiny detect and block matching programs that would expose sensitive data to unauthorized recipients or systems.
Restricts processing strictly to documented authorized uses, mitigating incorrect authorization decisions for sensitive data.
Addresses incorrect authorization by requiring independent verification of results and an opportunity to contest before any adverse action is taken.