KB5120249: Windows 10 Version 21H2 Security Update (August 2026)

Full tracking and change history for KB5120249

Released

2026-08-11

Last changed

2026-09-24

Changes tracked

8

Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.

Check if KB5120249 is installed

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Known issues, from Microsoft

Quoted from Microsoft's support article for KB5120249 (checked 2026-10-10). Verify against the article before acting.

Devices with an unrecommended BitLocker Group Policy configuration might be required to enter their BitLocker recovery key

Symptoms

Some devices with an unrecommended BitLocker Group Policy configuration might be required to enter their BitLocker recovery key on the first restart after installing this update.

This issue only affects a limited number of systems in which ALL the following conditions are true. These conditions are unlikely to be found on personal devices not managed by IT departments.

BitLocker is enabled on the OS drive.

The Group Policy Configure TPM platform validation profile for native UEFI firmware configurations is configured, and PCR7 is included in the validation profile (or the equivalent registry key is set manually).

System Information (msinfo32.exe) reports Secure Boot State PCR7 Binding as Not Possible .

The Windows UEFI CA 2023 certificate is present in the device’s Secure Boot Signature Database (DB), making the device eligible for the 2023‑signed Windows Boot Manager to be made the default.

The device is not already running the 2023-signed Windows Boot Manager.

In this scenario, the BitLocker recovery key only needs to be entered once -- subsequent restarts will not trigger a BitLocker recovery screen, as long as the group policy configuration remains unchanged. For help finding your BitLocker recovery key, see [Find your BitLocker recovery key](https://support.microsoft.com/Windows/Security/Encryption/find-your-bitlocker-recovery-key).

Enterprises are recommended to audit their BitLocker group policies for explicit PCR7 inclusion and check msinfo32.exe for their PCR7 binding status before installing this update.

Resolution

This issue is addressed in update KB5122878 . After installing update KB5122878, devices with this incompatible group policy configuration are prevented from installing the 2023-signed Windows Boot Manager. If your device was impacted, Event ID 1032 will appear in the System event log when installing Windows updates: "The Secure Boot update Boot Manager (2023) was not applied due to a known incompatibility with the current BitLocker configuration."

If you receive Event ID 1032 , Microsoft strongly recommends removing the Group Policy configuration before installing updates so that you can install the 2023-signed Windows Boot Manager and continue to receive the latest Secure Boot protection.

Remove the Group Policy configuration before installing the update (Recommended)

Open Group Policy Editor (gpedit.msc) or your Group Policy Management Console.

Navigate to: Computer Configuration > Administrative ...

CVEs fixed by this update

Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.

Scope and sources

Affected products

• Windows 10 Version 21H2 for 32-bit Systems
• Windows 10 Version 21H2 for ARM64-based Systems
• Windows 10 Version 21H2 for x64-based Systems

Also released in August 2026

KB5120228

215 CVEs · Critical · exploited

KB5120229

195 CVEs · Critical · exploited

KB5120233

215 CVEs · Critical · exploited

KB5120238

183 CVEs · Critical · exploited

KB5120240

170 CVEs · Critical · exploited

KB5120242

195 CVEs · Critical · exploited

KB5120385

144 CVEs · Critical · exploited

KB5120386

139 CVEs · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references

Official KB5120249 page (Microsoft Support)Microsoft Update CatalogMicrosoft Security Update Guide