Coming two and a half months after the second point release, Univention Corporate Server 4.2-3 is a small maintenance update that appears to mostly address various regressions reported by users from previous versions of the operating systems. These include more checks for Microsoft Active Directory (AD) domains and expanded configurability and usability of the management system. In addition to the new Microsoft AD checks, which enable displaying of information about known problems, as well as hints on how to fix them, the Univention Corporate Server 4.2-3 update integrates various security patches for core components, including the Linux kernel, Samba, and Asterisk. It also adds a bunch of new functional tests to the UMC diagnostic module.