A security flaw has been discovered in Dromara UJCMS up to 12.3.1. The affected element is the function usernameExist of the file ujcms-cms/src/main/java/com/ujcms/cms/core/web/api/UserController.java of the component UserController. Performing a manipulation of the argument Username results in improper authorization. It is possible to initiate the attack remotely. The project was informed of the problem early through an issue report but has not responded yet.