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 there are any questions or comments about this advisory:
- Send an email to [email protected]
Impact
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2026-47201 has a CVSS score of 8.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.0.0-20260528144335-a370d76d23c7); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-47201? CVE-2026-47201 is a high-severity improper input validation vulnerability in goauthentik.io (go), affecting versions < 0.0.0-20260528144335-a370d76d23c7. It is fixed in 0.0.0-20260528144335-a370d76d23c7. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2026-47201? CVE-2026-47201 has a CVSS score of 8.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of goauthentik.io are affected by CVE-2026-47201? goauthentik.io (go) versions < 0.0.0-20260528144335-a370d76d23c7 is affected.
- Is there a fix for CVE-2026-47201? Yes. CVE-2026-47201 is fixed in 0.0.0-20260528144335-a370d76d23c7. Upgrade to this version or later.
- Is CVE-2026-47201 exploitable, and should I be worried? Whether CVE-2026-47201 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-47201 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-47201? Upgrade
goauthentik.ioto 0.0.0-20260528144335-a370d76d23c7 or later.