OSCAL-GUI contains a reflected cross-site scripting vulnerability that allows unauthenticated attackers to execute arbitrary JavaScript in a victim's browser by injecting malicious content through the project request parameter in oscal-forms.php. The parameter value is URL-decoded and assigned to the project_id variable without sanitization in oscal-functions.php, and when the supplied project ID is not found, the unsanitized value is concatenated into an error message via the Messages() function and reflected into the HTML response body without encoding.