Skip to main content

CVE-2026-47201

XML Signature Wrapping in SAML Source ACS allows authentication as arbitrary federated user​

Summary​

authentik's SAML Source ACS endpoint is vulnerable to XML Signature Wrapping when validating upstream SAML responses. An attacker with any account at the upstream IdP can reuse a valid signed assertion to authenticate as another federated user.

Patches​

authentik 2026.5.1, 2026.2.4 and 2025.12.6 fix this issue.

Impact​

Affected: authentik deployments using a SAML Source for upstream SAML federation with signed assertions, or signed responses without signed assertions. Not affected: deployments that do not use SAML Source for upstream SAML federation.

The SAML Source trusts that the verified XML signature belongs to the assertion or response that authentik later consumes. A crafted SAML response can make signature verification succeed against the attacker's original signed assertion while authentik reads identity data from a different forged assertion.

An attacker first completes a legitimate login to the upstream IdP and captures the signed SAML response sent through their browser. They then submit a modified response to the ACS endpoint where the valid signature still verifies, but the consumed assertion contains a victim identifier or attacker-chosen attributes.

The attacker can authenticate as a victim who has previously used the SAML Source, or as a local user matched by forged email or username when those matching modes are enabled.

Workarounds​

Disable affected SAML Sources, or block access to their ACS endpoints.

For more information​

If you have any questions or comments about this advisory: