DotVVM is an open source MVVM framework for web applications. Prior to 4.2.11, 4.3.15, and 5.0.0-preview09-final, AuthorizeActionFilter performs no authorization because its explicit ICommandActionFilter.OnCommandExecutingAsync, IViewModelActionFilter.OnViewModelCreatedAsync, and IPresenterActionFilter.OnPresenterExecutingAsync implementations return completed tasks instead of invoking the corresponding checks. Applications relying on this filter can therefore expose protected commands, view models, or presenters to unauthorized requests without any special bypass technique. AuthorizeAttribute correctly implements the same interfaces and can be used as a workaround. This issue is fixed in versions 4.2.11, 4.3.15, and 5.0.0-preview09-final.