Microsoft has launched an pressing investigation into extreme stability points plaguing the January 2026 safety replace for Home windows 11, following studies that the patch is inflicting vital boot failures on bodily units.
The replace, recognized as KB5074109, was meant to convey safety enhancements to Home windows 11 variations 25H2 and 24H2 however has as a substitute triggered a wave of “UNMOUNTABLE_BOOT_VOLUME” errors that render affected methods unusable.
Vital Boot Failures Confirmed
The first concern underneath investigation entails units coming into a boot loop or displaying a “Black Display screen of Dying” instantly after making use of the January 13, 2026, Patch Tuesday replace.
Affected customers report seeing a cease code 0xED (UNMOUNTABLE_BOOT_VOLUME) accompanied by the message: “Your gadget bumped into an issue and desires a restart.”.
Microsoft has acknowledged the issue, stating they’ve acquired “a restricted variety of studies” the place units can’t full startup.
Notably, this regression seems to have an effect on solely bodily {hardware}, with digital machine environments presently displaying no indicators of the defect, Askwoody noticed first.
For directors and customers struck by this bug, the working system turns into inaccessible, requiring guide intervention through the Home windows Restoration Setting (WinRE) to uninstall the defective package deal.
Whereas the boot failure represents essentially the most extreme regression, KB5074109 can be answerable for a broader array of system-breaking bugs. Experiences verify that customers who efficiently boot are encountering widespread stability issues, together with complete system lockups and graphics driver conflicts.
In response to person documentation, the replace has launched vital regressions within the graphics stack, resulting in freezes in GPU-intensive purposes. Particular incidents have been recorded with BforArtists 5.0 (a Blender fork), the place switching viewport shading modes causes the system to hold indefinitely with out producing a blue display screen.
These “silent” lockups are attributed to conflicts between the brand new kernel adjustments and present DirectX/GPU drivers, with Nvidia and AMD methods additionally affected by black screens the place the Home windows UI fails to render appropriately.
The fallout from KB5074109 extends to enterprise connectivity and productiveness apps. Microsoft confirmed that the replace broke credential prompts for Azure Digital Desktop (AVD) and Home windows 365, stopping distant connections, a vital flaw that was subsequently patched through the out-of-band replace KB5077744 on January 17.
Moreover, Outlook Traditional customers have reported the applying freezing on launch or failing to sync POP/SMTP accounts as a result of lingering processes.
Mitigation Technique
For customers experiencing the UNMOUNTABLE_BOOT_VOLUME error, the one present recourse is to enter WinRE and uninstall the newest high quality replace. For these with bootable however unstable methods, Microsoft and safety consultants advocate pausing updates or rolling again KB5074109 through:
Settings > Home windows Replace > Replace historical past > Uninstall updates.
Enterprise directors are suggested to deploy Recognized Challenge Rollback (KIR) insurance policies the place accessible, whereas shoppers are urged to delay set up till Microsoft releases a complete repair for model 25H2.
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