ZITADEL is an open source identity management platform. From version 4.0.0 to 4.11.1, a vulnerability in Zitadel's login V2 interface was discovered that allowed a possible account takeover via XSS in /saml-post Endpoint. This issue has been patched in version 4.12.0.

Affected: Go: github.com/zitadel/zitadel, Go: github.com/zitadel/zitadel/v2

### Summary

A vulnerability was discovered in Zitadel's login V2 interface that allowed a possible account takeover.

### Impact

Zitadel exposes an HTTP endpoint named /saml-post. This endpoint is used for handling requests to SAML IdPs and accepts two HTTP GET parameters: url and id. When these parameters are supplied, users’ browsers auto-submit an HTTP POST request to the provided url parameter. The endpoint insecurely redirects users using the provided url GET parameter. As a result, by specifying a javascript: scheme, malicious JS code could be executed on Zitadel users’ browsers.

The endpoint also reflects user-supplied input in the server response, without HTML-encoding it. As a result, it is possible to inject arbitrary HTML code, which again leads to malicious JS code execution in the Zitadel users’ browsers.

An unauthenticated remote attacker can exploit these XSS vulnerabilities, and thus, execute malicious JavaScript code on behalf of Zitadel users. By doing so, such an attacker could reset the password of their victims, and take over their accounts.

It's important to note that this specific attack vector is mitigated for accounts that have Multi-Factor Authentication (MFA) or Passwordless authentication enabled.

### Affected Versions

Systems running one of the following versions are affected: - **4.x**: `4.0.0` through `4.11.1` (including RC versions) Important Note: Although this /saml-post endpoint is used when Zitadel is integrated with a SAML Ide…