A Cross-site Scripting (XSS) vulnerability exists when Team Foundation Server does not properly sanitize user provided input. An authenticated attacker could exploit the vulnerability by sending a specially crafted payload to the Team Foundation Server, which will get executed in the context of the user every time a user visits the compromised page.
The attacker who successfully exploited the vulnerability could then perform cross-site scripting attacks on affected systems and run script 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, execute malicious code, and use the victim's identity to take actions on the site on behalf of the user, such as change permissions and delete content.
The security update addresses the vulnerability by ensuring that Team Foundation Server sanitizes user inputs.