8.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-47201

CVE-2026-47201: authentik: XML Signature Wrapping in SAML Source ACS allows authentication as arbitrary federated user

authentik is an open-source identity provider. Prior to versions 2025.12.5, 2026.2.3, and 2026.5.1, 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. This issue has been patched in versions 2025.12.5, 2026.2.3, and 2026.5.1.

(GitHub Advisory)

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CVE-2026-47201

CVE-2026-47201:

8.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
goauthentik.io	go	< 0.0.0-20260528144335-a370d76d23c7	0.0.0-20260528144335-a370d76d23c7

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in authentik's SAML Source ACS endpoint, which was susceptible to XML Signature Wrapping (XSW). The core of the issue was in the signature verification process for SAML responses. The application would verify that a signature was cryptographically valid but failed to ensure that the signature corresponded to the correct part of the SAML document that was being processed for user authentication. This allowed an attacker to take a legitimately signed SAML assertion, include it in a crafted response alongside a forged assertion, and trick the system. The signature from the legitimate assertion would be validated, but the system would then proceed to use the identity information from the attacker's forged assertion. This could allow an attacker to impersonate any other federated user.

The patch addresses this by modifying the signature verification logic. The key change is in the _verify_signature function within authentik/sources/saml/processors/response.py. It now requires the specific XML element that is expected to be signed (the target) as an argument. It then explicitly checks that the Reference URI inside the XML Signature points directly to the ID of this target element. This ensures that the signature being verified is undeniably linked to the data being consumed, effectively preventing the signature from being wrapped around malicious content. The functions _verify_response_signature and _verify_assertion_signature were updated to call the new, more secure _verify_signature with the correct target element (either the whole response or the specific assertion).

Vulnerable functions

ResponseProcessor._verify_signature

authentik/sources/saml/processors/response.py

The original `_verify_signature` function was vulnerable to XML Signature Wrapping because it only checked the cryptographic validity of the signature, not what element it was signing. An attacker could reuse a valid signature and apply it to a different, malicious element in the SAML response. The patch fixes this by requiring a `target` element to be passed and verifying that the signature's Reference URI points to this target element.

ResponseProcessor._verify_response_signature

authentik/sources/saml/processors/response.py

This function was vulnerable because it used the flawed `_verify_signature` method without ensuring the signature corresponded to the main response element. The fix passes the response's root element (`self._root`) to the patched `_verify_signature` function, ensuring that the signature being verified is for the entire response.

ResponseProcessor._verify_assertion_signature

authentik/sources/saml/processors/response.py

This function was vulnerable because it called the flawed `_verify_signature` method and did not reliably link the signature to the assertion it was supposed to be signing. An attacker could craft a response where a valid signature was used to verify a malicious assertion. The patch fixes this by explicitly getting the parent assertion of the signature and passing it as the target for verification.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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