A cross-site-scripting (XSS) vulnerability exists when Active Directory Federation Services (ADFS) does not properly sanitize certain error messages. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected ADFS server.
The attacker who successfully exploited the vulnerability could then perform cross-site scripting attacks on affected systems and run scripts in the security context of the current user. The attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim's identity to take actions on the ADFS site on behalf of the user, such as change permissions and delete content, and inject malicious content in the browser of the user.
The security update addresses the vulnerability by helping to ensure that ADFS error handling properly sanitizes error messages.