Overview
- New out-of-band updates such as KB5078127 (Windows 11 25H2/24H2), KB5078132 (Windows 11 23H2), and KB5078129 (Windows 10) restore Outlook and other cloud‑file workflows that broke after the January 13 security update.
- Microsoft confirms the bug primarily hit classic Outlook configurations using POP accounts or PST files stored in cloud services like OneDrive or Dropbox, causing hangs, missing Sent Items, and repeated downloads.
- The emergency fixes are cumulative and include the January 13 security patches and the January 17 out-of-band update, and they can be installed via Windows Update or the Microsoft Update Catalog.
- Devices that are not experiencing these issues do not need the new updates, and Microsoft cautions that uninstalling the January security update leaves systems exposed to vulnerabilities.
- Microsoft is investigating reports of some physical PCs failing to boot with UNMOUNTABLE_BOOT_VOLUME after the January update, while earlier regressions included Remote Desktop sign-in failures and shutdown issues now addressed by prior patches.