Update 7/15/2025: Added a mention of Exchange 2016/2019 ESU program.
In May 2024, we shared our Exchange Server Roadmap Update and our plans for the future of Exchange Server. Since then, we’ve bee...
Updated Aug 13, 2025
Version 17.0
Blog Post
Rollback of Exchange Migration caused by Windows Update KB5065426
On September 9, 2025, Microsoft released Security Update KB5065426 (OS Build 26100.6584).
During our ongoing Exchange migration, we discovered that this update triggered severe issues in combination with VMware.
What Happened?
When deploying new virtual machines, VMware reported no Sysprep errors.
In reality, however, the MachineSID was not regenerated — a critical step to ensure unique system identities.
As a result, several systems ended up with duplicate SIDs. The issue was first identified after installing KB5065426 on Windows Server 2025, but reports indicate that Windows 11 and Windows Server 2022 may also be affected under certain VMware build versions.