Microsoft Active Directory Federation Services (AD FS) 1.x through 2.1 on Windows Server 2003 R2 SP2, Windows Server 2008 SP2 and R2 SP1, and Windows Server 2012 allows remote attackers to obtain sensitive information about the service account, and possibly conduct account-lockout attacks, by connecting to an endpoint, aka "AD FS Information Disclosure Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A18318
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-066