A cross-site-scripting security issue in the uninstall package feature was reported by Ngo Van Thien, Sun* Inc.
Since this vulnerability requires a user to be authenticated this is only a low impact security issue for most sites.
The issue affects UliCMS Version 2018.4 to 2020.1.
The security hotfix FixPackageControllerXSS was released for UliCMS 2019.4 to 2020.1.
If you still use an older release of UliCMS you should upgrade to a supported version and then install the patch.
Version 2020.2 will include the fix at release state.