A spoofing vulnerability exists when Microsoft browsers improperly handles specific redirects. An attacker who successfully exploited this vulnerability could trick a user into believing that the user was on a legitimate website. The specially crafted website could either spoof content or serve as a pivot to chain an attack with other vulnerabilities in web services.
To exploit the vulnerability, the user must either browse to a malicious website or be redirected to it. In an email attack scenario, an attacker could send an email message in an attempt to convince the user to click a link to a malicious site.
In a web-based attack scenario, an attacker could host a specially crafted website designed to appear as a legitimate website to the user. However, the attacker would have no way to force the user to visit the specially crafted website. The attacker would have to convince the user to visit the specially crafted website, typically by way of enticement in an email or instant message.
The security update addresses the vulnerability by correcting how browsers handles specific redirects.