Vulnerability in authentik (CVE-2026-40165)
Summary
Vulnerability in authentik (CVE-2026-40165). Confidential information can be exposed externally. 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. Versions 2025.12.4 and prior, and versions 2026.2.0 through 2026.2.2 were vulnerable to Authentication Bypass through SAML NameID XML Comment Injection. Due to how authentik extracted the NameID value from a SAML assertion, it was possible for an attacker to trick authentik into only seeing a part of the NameID value, potentially allowing an attacker to gain access to other accounts. This issue could be exploited on an authentik instance with a SAML Source, where the attacker had an account on the SAML Source and the ability to modify their NameID value (commonly username or E-mail), and XML Signing was enabled. The attacker could modify the SAML assertion given to authentik by injecting a comment within the NameID value, which effectively truncated the NameID value to the snippet before the comment, and gave the attacker access to any user account. This issue has been fixed in versions 2025.12.5 and 2026.2.3.
Source: NIST National Vulnerability Database NVD
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-2026-40165 has been found in authentik.
Confidential information can be exposed externally. CVSS score: 8.7/10.
What to do: upgrade authentik to 2025.12.5, 2026.2.3 or later.
If unsure, ask your IT team or search "authentik CVE-2026-40165" on the vendor's site.
CVE-2026-40165 (authentik) — CWE-91 / CVSS v3 8.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
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.
A vulnerability (CWE-91) exists in authentik.
Check the vendor advisory for the affected versions of authentik.
Severity: High (CVSS 8.7/10). Confidential information can be exposed externally.
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 request patterns matching this CVE's known IOCs. 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
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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。 -
2Apply 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を含めること。
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3Post-deployment verification verify
Confirm patched version is live in production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。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。