The vulnerability exists in the openUrl function of the @a2ui/web_core package by Google, where an attacker-controlled URL is passed directly to window.open() without proper validation of the URI scheme. This allows an attacker to supply a javascript: URI as the url argument in a Button component's functionCall action. When a user clicks the button, arbitrary JavaScript executes within the context of the victim application's browser origin. This constitutes a stored or reflected cross-site scripting (XSS) vulnerability with a CVSS 4.0 base score of 6.1 (medium severity). The issue affects multiple versions including 0.9.0 through 0.10.1 and requires no non-default configuration as the Basic Catalog is enabled by default. No official remediation or patch has been published as of the data provided.

Successful exploitation allows an attacker to execute arbitrary JavaScript in the context of the victim application's browser origin. This can lead to actions such as session hijacking, unauthorized actions on behalf of the user, or other malicious behaviors typical of XSS vulnerabilities. The vulnerability is rated medium severity with a CVSS score of 6.1 and does not require elevated privileges or complex attack vectors.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should avoid using affected versions or implement additional input validation and sanitization on URLs passed to window.open(). Consider disabling or restricting the use of the Button component's functionCall action with user-controlled URLs if feasible.