Microsoft has officially acknowledged a significant issue with the Windows 11 update KB5089549, which has been confirmed to cause installation failures on some systems. Concurrently, a growing number of user complaints indicate that the update is also leading to slower internet connections. These widespread issues have escalated from forum discussions to a confirmed problem acknowledged by Microsoft.
The installation problem, now officially recognized by the company, is particularly affecting computers with very limited free space on their EFI partition, specifically 10MB or less. While Microsoft has confirmed this specific installation error, the reports of slow internet speeds are still largely based on user testimonials, though the sheer volume of these reports suggests a broader problem.
KB5089549, a Critical Windows 11 Update, Faces Major Installation Failures
The KB5089549 update was released less than a week ago for Windows 11 versions 25H2 and 24H2 (builds 26200.8457 and 26100.8457). Beyond its usual security enhancements, the update includes cumulative improvements from previous patches and various system tweaks.
The confirmed installation failure, marked by error code 0x800f0922, occurs on systems with insufficient EFI partition space. According to Microsoft, the installation may proceed normally until the reboot phase, where it fails around 35-36%, prompting Windows to undo the changes and display an error message.
Microsoft has proposed two solutions. The first involves opening the Command Prompt as an administrator and executing the following command:
reg add “HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc” /v EspPaddingPercent /t REG_DWORD /d 0 /f
After running the command, users should restart their computer and attempt to install KB5089549 again via Windows Update. Microsoft cautions that incorrectly modifying the Windows registry can lead to serious problems, advising this solution only for users who are experiencing the 0x800f0922 error and are confident in their technical abilities.
The second solution is to wait for the Known Issue Rollback (KIR) system to automatically apply the fix. KIR is Microsoft’s mechanism for automatically reverting problematic changes without user intervention. Microsoft states that this mitigation has already been deployed to consumer devices and unmanaged enterprise devices. For managed enterprise environments, a specific Group Policy update, “KB5089549 260514_06221 Known Issue Rollback,” is available for Windows 11 25H2 and 24H2, which needs to be installed and configured through the Computer Configuration > Administrative Templates path, followed by a device restart.
Slow Internet Speeds Reported Following the Update
In addition to installation woes, a second major concern has emerged: significantly slower internet speeds after installing KB5089549. While Microsoft has not yet officially confirmed a widespread network failure affecting either LAN or WiFi, the increasing number of user reports is drawing significant attention.
Many users have reported a noticeable drop in internet speeds immediately after installing KB5089549. Reports on Microsoft Q&A and Reddit detail instances of organizations experiencing slow network performance on multiple systems after applying the patch to Windows 11 25H2. In these cases, network infrastructure and internet providers have been checked without finding any issues, suggesting the problem is isolated to the updated Windows machines.
While the installation error related to the EFI partition is 100% confirmed, the slow internet issue remains in the reporting phase. Despite this, it has become another critical point of focus for an update that was intended to enhance Windows 11’s stability and security. The installation of KB5089549 has proven to be a significant headache for Microsoft, although they have at least addressed the most critical installation problem, and further announcements regarding the internet speed issues are anticipated.
