A vulnerability exists in certain .Net Framework API's and Visual Studio in the way they parse URL's. An attacker who successfully exploited this vulnerability could use it to bypass security logic intended to ensure that a user-provided URL belonged to a specific hostname or a subdomain of that hostname. This could be used to cause privileged communication to be made to an untrusted service as if it was a trusted service.To exploit the vulnerability, an attacker must provide a URL string to an application that attempts to verify that the URL belongs to a specific hostname or to a subdomain of that hostname. The application must then make an HTTP request to the attacker-provided URL either directly or by sending a processed version of the attacker-provided URL to a web browser.