Important Security Updates for Windows 10 in August 2026

On August 14, 2026, Microsoft released an important security update designated KB5120249 for Windows 10 versions 22H2 and 21H2. This update also affects Windows 10 Enterprise LTSC 2021 and Windows 10 IoT Enterprise LTSC 2021. As is customary with monthly Patch Days, this update does not introduce new features but addresses critical security vulnerabilities in the operating system. Update KB5120249 resolves several specific issues.

Among other things, it corrects a bug that can cause automatic backups of the file version history to fail on network shares via Server Message Block (SMB) with the error message "Invalid Credentials." This issue can result in scheduled backups not copying files, jeopardizing data security. Another important aspect of the update is the enhancement of Secure Boot functionality. Microsoft has added additional, highly reliable data for device targeting. This expands the coverage of devices that can automatically receive new Secure Boot certificates.

The distribution of these certificates via Windows Updates will continue over the coming months on supported PCs and unmanaged enterprise devices. In addition to security improvements, Microsoft is also updating Windows Defender, the .NET Framework, and the Windows Malicious Software Removal Tool. These updates are part of Microsoft's ongoing efforts to ensure the security and stability of the operating system. To receive update KB5120249, it will be automatically installed on Windows 10 systems that have subscribed to the Extended Security Updates (ESU) for Windows 10. The installation of the update should take only a few minutes.

Alternatively, users can manually download the update from the Microsoft Update Catalog, with the file size being under 1 gigabyte. Participation in the ESU program is crucial, as support for Windows 10 without this program ended on October 14, 2025. Computers that do not participate in the ESU program have been unprotected against newly discovered security vulnerabilities since then. The ESU program ensures that Windows 10 continues to receive security updates until October 12, 2027.

In recent years, Microsoft has increasingly focused on the security of its operating systems, particularly in light of the growing threats from cyberattacks. Regular security updates are part of this strategy to protect system integrity and secure user data. Update KB5120249 is another step in the continuous improvement of the Windows 10 platform. Users are strongly urged to install the update immediately to protect their systems from potential security risks. Microsoft plans to continue the rollout of the new Secure Boot certificates until the end of 2026.