How severe is CVE-2026-40166?

CVE-2026-40166 has a CVSS 4.0 base score of 7.1, rated high severity.

Is CVE-2026-40166 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-40166?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-40166 have an EU (EUVD) identifier?

Yes. CVE-2026-40166 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31490.

When was CVE-2026-40166 published?

CVE-2026-40166 was published on 2026-05-22 and last updated on 2026-06-17.

CVE-2026-40166

CVE-2026-40166 is a high-severity vulnerability with a CVSS 4.0 base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-200.

Key facts

Severity: High (CVSS 4.0 base score 7.1)
EPSS exploit prediction: 0% (26th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-31490
Weakness: CWE-200
Published: 2026-05-22
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-40166?: 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.
How severe is CVE-2026-40166?: CVE-2026-40166 has a CVSS 4.0 base score of 7.1, rated high severity.
Is CVE-2026-40166 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-40166?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-40166 have an EU (EUVD) identifier?: Yes. CVE-2026-40166 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31490.
When was CVE-2026-40166 published?: CVE-2026-40166 was published on 2026-05-22 and last updated on 2026-06-17.

References

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