Microsoft has released an emergency update to fix a server authentication problem affecting Domain Controllers (DC) running supported versions of Windows Server.

The issue prevents users from logging into services or applications that use Single Sign-On (SSO) in Active Directory On premises or hybrid Azure Active Directory environments.

In its statement accompanying the update, Microsoft stated that it is “a known issue that might cause authentication failures related to Kerberos tickets you acquired from Service for User to Self (S4U2self). This issue occurs after you install the November 9, 2021 security updates on domain controllers (DC) that are running Windows Server.”

In order to install the updates, users are advised to download the update package by searching the Microsoft Update Catalogue. Afterwards, they can import the update into Windows Server Update Services (WSUS) following instructions in the Microsoft Update Catalogue.