The October 10, 2023, Cumulative Update (KB5031358) for Windows 11 (OS Build 22000.2538) was a critical security release specifically targeting Windows 11 version 21H2.
Notably, this update marked the End of Servicing for the original version of Windows 11 (21H2) on Home and Pro editions. Devices remaining on this version after this patch no longer receive monthly security or quality updates. Key Improvements & Fixes
This update addressed several security vulnerabilities, including three zero-day flaws.
Security Patches: Fixed critical vulnerabilities such as the HTTP/2 Rapid Reset Attack (CVE-2023-44487) and an information disclosure flaw in Microsoft WordPad (CVE-2023-36563).
Performance & Stability: Resolved a user-mode memory leak occurring during file copy/move operations and fixed a handle leak related to Microsoft Defender for Endpoint. Application & Hardware Fixes:
Addressed an issue where Microsoft Defender prevented some USB printers from printing.
Fixed a bug where OneDrive files compressed by NTFS caused Windows to stop responding.
Updated the spelling of Ukraine’s capital from Kiev to Kyiv and added support for Greenland's daylight saving time changes. The October 10, 2023, Cumulative Update (KB5031358) for
Resolved account lockout issues (Event 4625) when usernames were in User Principal Name (UPN) format. Widely Reported Installation Issues
Despite its importance, many users encountered significant difficulty installing KB5031358.
Error 0x800f0988: A common error where the update would fail or get stuck at specific percentages (often 34%).
Persistent Failures: Some users reported that even a full PC wipe and clean install did not resolve the installation error.
Troubleshooting Steps: Common community-recommended fixes included running the Windows Update Troubleshooter, clearing the SoftwareDistribution cache, or manually downloading the standalone package from the Microsoft Update Catalog. Known Issues Post-Update
BitLocker Errors: Some managed devices incorrectly received a 65000 error in Mobile Device Management (MDM) regarding drive encryption.
Currency Locale: Systems set to the Croatia locale might not have displayed the expected currency. Severity: Important x64 Impact: Allows an attacker to
Since this was the final update for version 21H2, users are strongly encouraged to upgrade to Windows 11 22H2 or newer to continue receiving security protection.
The KB5031358 update, released on October 10, 2023, is a mandatory security update for Windows 11, version 21H2. This was a significant release as it marked the final security update for several editions of Windows 11 21H2 (Home, Pro, and Pro Education) before they reached their end of servicing. Update Highlights
Security Fixes: Addresses three critical zero-day vulnerabilities, including the HTTP/2 Rapid Reset attack (CVE-2023-44487), a WordPad information disclosure (CVE-2023-36563), and a Skype for Business privilege escalation (CVE-2023-41763).
New Features: Includes elements from the "Moment 4" update, such as a preview of Copilot in Windows, a new Windows Backup app, and updates to the Settings app and Taskbar.
Quality Improvements: Fixes an issue where Microsoft OneDrive became unresponsive when using NTFS-compressed files and addresses a USB printer conflict where Microsoft Defender prevented printing. Installation Details
Target Systems: x64-based and ARM64-based systems running Windows 11 version 21H2.
OS Build: After installation, your system build number will advance to 22000.2538. net stop wuauserv
Download: This update is typically delivered via Windows Update automatically. If it fails, you can manually download it from the Microsoft Update Catalog. Common Troubleshooting
If you encounter errors like 0x800f0988 or 0x800f081f while installing, try these community-recommended steps: KB5031358 (OS Build 22000.2538)
As of today, newer cumulative updates (like KB5033375 from December 2023 or KB5044285 from October 2024) include all fixes in KB5031358 plus more. However, there are two scenarios where seeking out KB5031358 is justified:
Recommendation: For most users, install the latest cumulative update. But for legacy x64 validation, KB5031358 remains a high-quality, security-hardened fallback.
KB5031358 elevates Windows 11 22H2 to build 22621.2428.
Severity: Critical (Remote Code Execution & Elevation of Privilege).
Impact: Requires restart. Adds Copilot infrastructure, fixes 3 zero‑days.
Top risk: BitLocker recovery prompt on some NVMe drives.
Rollback available: 30 days via standard uninstall.
Note: This update does not apply to Windows 11 24H2, 23H2 (which has its own CUs), or ARM64 devices. For ARM64, use KB5031358 (ARM64).
A: Yes, but only if you have applied the May 2023 servicing stack update first. Microsoft officially moved 21H2 to the same cumulative payload as 22H2 starting October 2023.
UrlMon.dll 64-bit.Additionally, the update includes fixes for two zero-day vulnerabilities that were being actively exploited prior to October 2023:
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