New Update Microsoft issues SECOND emergency out of band update for Windows 11 to address disastrous Patch Tuesday bugs — KB5078127 released globally

While the previous advisory recommended immediate patching via KB5078127 to fix application errors (Outlook/Dropbox), new evidence indicates that the underlying January 2026 update (KB5074109) is causing catastrophic boot failures on physical hardware. Systems are failing with the stop code UNMOUNTABLE_BOOT_VOLUME, rendering them unbootable without manual recovery. Administrators should immediately halt the deployment of KB5074109 to critical physical systems until a definitive fix is confirmed.

Given the risk of total system loss, I am revising the previous recommendation for home and enterprise users.

Halt Automated Updates
If your system has NOT yet installed the January update, go to Settings > Windows Update and Pause updates for 1 week immediately to avoid the unbootable state.

Enterprise Postponement
Per NIST 800-40 (Patch Management), administrators should move from "Immediate" to "Hold" for KB5074109 for any physical workstation fleet.

Manual Recovery if Impacted
If you are already facing the <span>UNMOUNTABLE_BOOT_VOLUME</span> error, you must use the Windows Recovery Environment (WinRE).

Boot from a Windows 11 installation media.
Select Repair your computer > Troubleshoot > Advanced Options > Command Prompt.
Attempt a disk repair using chkdsk /f C:.
If that fails, use Uninstall Updates from the Advanced Options menu to remove the latest Cumulative Update.

Feedback Loop
Microsoft is actively requesting logs via the Feedback Hub app for users who can still access their desktop.

Caution
No setup is 100% secure, but in this specific instance, the risk of an unbootable system outweighs the immediate need for the January security patches. Wait for Microsoft to release a "Fixed" version of the Cumulative Update or a specific Kir (Known Issue Rollback).

References
Microsoft Investigation (Jan 25, 2026)
"Windows 11 boot failures after January updates"

NIST SP 800-40
Patch Management discipline regarding "Emergency Rollbacks."
 
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Divine_Barakah said:
I do too take system images before installing W U, but unfortunately I had just received my laptop and after installing Windows the Jan update got installed.

The only problem I am experiencing is that my device never gets in hibernation when I close the lid. I left if for about 15 hours and it was in sleep.
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According to the hotfix details, the issue of sleep/hibernation has been fixed. I'll keep the updates paused for now as I am not ready for other surprises.
 
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Divine_Barakah said:
I'll keep the updates paused for now as I am not ready for other surprises.
Click to expand...
Why? When Windows Update offers the update, just don't install it. Don't even pay attention to it and Windows will install the update itself when it's ready. It's not that hard. Pretend like Windows Update doesn't exist at all.
 
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Parkinsond said:
You are using W 11 IoT LTSC just like me; I have no issues; you should be okay too, unless you have MS store installed while this issue is related to.
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Now I am using Windows 11 Pro 25H2 on both of my laptops
Marko :) said:
Why? When Windows Update offers the update, just don't install it. Don't even pay attention to it and Windows will install the update itself when it's ready. It's not that hard. Pretend like Windows Update doesn't exist at all.
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The update was installed automatically on my Thinkpad, but not my Dell. The update broke hibernation and when I leave my laptop on with the lid closed it stays running and I have just realised it does not even sleep. It just turns off the screen.
 
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Divine_Barakah said:
Honestly I am lost. Wasn't it supposed to be a security update? Or was it a quality one? I thought security updates were supposed to fix vulnerabilities not break things.
Click to expand...
Systems using certain SSD firmware versions, RAID modes, legacy drivers, or encryption setups are more likely to hit this. The update changes expectations, but the driver or firmware doesn’t respond the way Windows now expects, so mounting the boot volume fails.

Click to expand...
 
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I have set up WSUS on my home server a few years ago. I've added a my own 60-day rollout period for any updates (security or feature).

All my machines use it for updates and I never bothered with these issues again.

I swear I will eventually get around moving everything to Linux. I can't stand microslop anymore with their crap.
 
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Parkinsond said:
Linux will stay in the "but it is not perfect" forever, unless sponsored by a giant tech company; ToyOS.
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The best thing about Linux distro is the fact they are not sponsored by big tech, but it is also a problem of fragmentation. Linux is community-driven but it is too fragmented and there are countless distros.
 
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Divine_Barakah said:
The best thing about Linux distro is the fact they are not sponsored by big tech, but it is also a problem of fragmentation. Linux is community-driven but it is too fragmented and there are countless distros.
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Linux is an OS, not just a small app with no need for much maitanance such as 7-zip; without generous sponsor, it will stay ToyOS.
 
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Parkinsond said:
Linux is an OS, not just a small app with no need for much maitanance such as 7-zip; without generous sponsor, it will stay ToyOS.
Click to expand...
Most of the distributions are generously sponsored but it's just devs are lazy to do a good jog generally, as there is not much control and not much incentive.

Everyone does whatever they want and if they want.
 
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Divine_Barakah said:
Calling Linux a toyOS is so belittling. Linux is btw used on countless servers. Let's not forgot about Linux kernel.
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Home user use Linux as a toy, not for productivity.
For productivity, home user resort to Windows.
Market share figures can tell the current situation.
 
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Trident said:
Most of the distributions are generously sponsored but it's just devs are lazy to do a good jog generally
Click to expand...
That is even worse; I was looking for an execuse.
So the OS relies on "lazy" developers using your own words, not mine.
 
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