Information Disclosure in authentik (CVE-2026-40166)
Summary
Vulnerability in authentik (CVE-2026-40166). Risk of unauthorized operations or information disclosure. Exploitable via GET /api/v3/oauth2/access_tokens/.. Mitigation: upgrade to 2025.12.5, 2026.2.3 or later.
Original description
The description as published by the source.
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.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-40166 has been found in authentik.
Attackers can target a specific entry point like GET /api/v3/oauth2/access_tokens/. over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade authentik to 2025.12.5, 2026.2.3 or later.
If unsure, ask your IT team or search "authentik CVE-2026-40166" on the vendor's site.
CVE-2026-40166 (authentik) — CWE-200
Attack surface: GET /api/v3/oauth2/access_tokens/.
Patched: 2025.12.5, 2026.2.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Information disclosure (CWE-200) exists in authentik. Attackers reach the vulnerable code path via GET /api/v3/oauth2/access_tokens/..
Check the vendor advisory for the affected versions of authentik. Attack surface: GET /api/v3/oauth2/access_tokens/..
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 2025.12.5, 2026.2.3.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual GET /api/v3/oauth2/access_tokens/. requests with malformed payloads or SQL meta-characters. Run grep -r 'authentik' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'authentik' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
authentikを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'GET /api/v3/oauth2/access_tokens/.' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
GET /api/v3/oauth2/access_tokens/.への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply patch patch
Upgrade authentik to 2025.12.5, 2026.2.3ステージング環境で 2025.12.5, 2026.2.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
-
4Post-deployment verification verify
Replay attack against GET /api/v3/oauth2/access_tokens/. on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- web github.com
- web github.com