CVE-2026-41577: Authentik SAML Assertion Validation Bypass (CWE-345)

Technical summary

The SAML ResponseProcessor.parse() method in authentik versions prior to 2025.12.5 and 2026.2.3 does not enforce validation of the Conditions element within SAML assertions. Specifically, the NotBefore and NotOnOrAfter temporal constraints, as well as AudienceRestriction elements, are ignored during processing. This permits the acceptance of assertions beyond their validity window and assertions addressed to unintended service providers, contrary to the SAML 2.0 specification. The vulnerability is rooted in insufficient input validation during assertion processing (CWE-345: Insufficient Verification of Data Authenticity).

Business impact

Organizations deploying authentik as their identity provider face elevated risk of authentication bypass. An attacker able to obtain a valid SAML assertion—whether expired or intended for a different application—could reuse it to gain unauthorized access. The scope of impact depends on the sensitivity of protected applications and the attacker's ability to capture assertions. In environments where authentik serves multiple service providers, the risk multiplies, as assertions meant for one application could be weaponized against others.

Affected systems

Authentik versions prior to 2025.12.5 (in the 2025.12 release series) and prior to 2026.2.3 (in the 2026.2 release series) are affected. Organizations running authentik should verify their deployed version against these release tags. Versions 2025.12.5, 2026.2.3, and later are patched.

Exploitability

Exploitation requires network access to a service that accepts SAML assertions from the affected authentik instance. No user interaction or special privileges are required once an assertion is obtained. The attacker must either intercept a legitimate assertion or recover one from logs or cache. The base CVSS vector (7.5, HIGH) reflects the combination of low attack complexity and high integrity impact, though the attack does not affect confidentiality or availability directly.

Remediation

Upgrade authentik to version 2025.12.5 or later if running the 2025.12 series, or to version 2026.2.3 or later if running the 2026.2 series. Verify the patch by checking the release notes and confirming the ResponseProcessor now properly validates Conditions. No interim workarounds are documented; patching is the primary mitigation.

Patch guidance

Apply the patched versions 2025.12.5 or 2026.2.3 as appropriate to your deployment. Review your authentik deployment architecture before patching to minimize service interruption. Test the patch in a non-production environment to confirm compatibility with your connected service providers. After patching, audit your SAML assertion logs to detect any suspicious replay activity during the vulnerability window.

Detection guidance

Monitor SAML assertion logs for patterns indicative of replay attacks: repeated use of the same assertion ID, assertions being accepted after their NotOnOrAfter timestamp, or assertions with AudienceRestriction values that do not match the receiving service provider. Implement alerting on authentication failures followed by successes with identical assertion identifiers. Review authentik access logs for anomalous authentication patterns around the discovery date (2026-06-02).

Why prioritize this

This vulnerability should be prioritized for patching due to its direct impact on authentication integrity. A HIGH CVSS score coupled with low attack complexity reflects the practical risk. Organizations with multi-tenant or multi-service-provider SAML deployments face compounded risk. Although the KEV program has not flagged this issue, the authentication bypass vector and public disclosure warrant urgent attention.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) is driven by: (1) network-accessible attack vector with no prerequisites (AV:N/PR:N); (2) low attack complexity (AC:L); (3) high integrity impact (I:H), reflecting the ability to bypass authentication controls; and (4) no direct confidentiality or availability impact in the base scenario (C:N/A:N). The unchanged scope (S:U) indicates the impact is limited to the authorization logic of the affected component, not broader system compromise.

Frequently asked questions