An information disclosure vulnerability exists in the way that Microsoft Edge handles cross-origin requests. An attacker who successfully exploited this vulnerability could determine the origin of all webpages in the affected browser.
In a web-based attack scenario, an attacker could host a website that is used to attempt to exploit the vulnerability. Additionally, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could be used to exploit the vulnerability. However, in all cases an attacker would have no way to force users to view attacker-controlled content. Instead, an attacker would have to convince users to take action. For example, an attacker could trick users into clicking a link that takes them to the attacker's site.
The security update addresses the vulnerability by correcting how Microsoft Edge handles cross-origin requests.