Historically, Exchange utilized BinaryFormatter serialization, a method that, while efficient, was prone to deserialization attacks—a common vector for remote code execution. CU12 introduced the capability to change the serialization mode to JsonFormatter . While this change was not enabled by default immediately upon installation, CU12 provided the necessary groundwork for administrators to switch to a more secure serialization method. This update was a direct response to the evolving threat landscape, forcing organizations to modernize their security posture. By prioritizing the mitigation of deserialization vulnerabilities, CU12 marked a turning point in the hardening of on-premises Exchange environments.
Navigating the Critical Update: An Analysis of Exchange Server 2019 Cumulative Update 12 exchange 2019 cu12
Technical Overview: Microsoft Exchange Server 2019 CU12 (KB5011156) This update was a direct response to the
: Added support for Multi-Factor Authentication (MFA) enabled admin credentials in Hybrid Management PowerShell cmdlets. was released on January 11, 2022
was released on January 11, 2022 . It is a cumulative update that includes all fixes, security updates, and changes from previous CUs. It also introduces new features and resolves known issues from earlier versions.