Microsoft Issues Another Emergency Patch to Fix Widespread Outlook and Cloud Storage Problems
Microsoft has released a second emergency out-of-band update for Windows 11 to address critical bugs introduced by the January 2026 Patch Tuesday security update. The mandatory patch, designated KB5078127, fixes problems affecting Outlook and third-party applications that work with cloud-based file storage.
What Problems Does KB5078127 Fix?
The emergency update addresses a significant bug where applications that open or save files stored in cloud-backed locations became unresponsive or displayed error messages. Outlook users experienced particularly severe issues, with the email client crashing or failing to open when PST files were stored in cloud-based services like OneDrive. The broader problem also affected other applications like Dropbox and OneDrive that rely on cloud file syncing.
Context: A Troubled Patch Tuesday Update
The January 2026 security update has proven to be one of Microsoft’s most problematic releases in recent memory. This is the second time this month that Microsoft has had to issue a last-minute fix for bugs related to its January security update. The original Patch Tuesday release, distributed on January 13, introduced multiple critical issues:
- Remote Desktop login failures across Azure-based sessions
- Shutdown and hibernation failures on Windows 11 version 23H2
- Boot failures with “UNMOUNTABLE_BOOT_VOLUME” errors on Windows 11 versions 25H2 and 24H2
- Sleep mode failures on some older systems
Which Versions Are Affected?
KB5078127 is rolling out to Windows 11 version 25H2 and version 24H2, bringing build numbers to 26200.7628 and 26100.7628 respectively. The update is mandatory and will download automatically through Windows Update.
Installation and Performance
The emergency patch takes approximately 5 minutes to download and 3 minutes to install, with a single reboot required. Users can check for the update manually by navigating to Settings > Windows Update > Check for updates, where it will appear as “2026-01 Update (KB5078127).”
Why Out-of-Band Updates Matter
Microsoft only issues out-of-band updates when there’s a serious issue that can’t wait until its regular update cycle. The fact that two such updates have been required within days of the January Patch Tuesday release underscores the severity of the issues introduced by the original security update.
What Users Should Do
While the mandatory nature of KB5078127 means it will eventually install automatically, users experiencing Outlook crashes or unresponsive applications with cloud file storage are encouraged to install it immediately. The update includes all protections and improvements from the original January 2026 Windows security update released January 13, as well as the first out-of-band update from January 17, ensuring users don’t miss critical security protections while addressing the reported bugs.