Critical Microsoft Vulnerability Allows Remote Code Execution (CVE-2026-21535)

Microsoft has disclosed a critical security flaw impacting multiple Windows versions. Tracked as CVE-2026-21535, this vulnerability carries a CVSS severity rating of 9.8 out of 10. Attackers can exploit it remotely without authentication.

Affected products include Windows 10 versions 21H2 through 23H2 and Windows Server 2022. Systems without recent security updates are vulnerable. Successful exploitation grants full control over compromised devices. Malicious actors could install malware or steal sensitive data.

The flaw exists in the Windows Kernel Transaction Manager component. Improper handling of object memory creates an elevation of privilege opportunity. Microsoft confirmed active exploitation attempts in limited attacks. Immediate patching is required.

Mitigation steps:

1. Apply Microsoft's security update via Windows Update
2. Verify installation of KB502XXXXX (specific bulletin)
3. Restart systems after patching
4. Monitor for suspicious process creation events

Microsoft released patches on October 10, 2026. Administrators should prioritize this update above non-critical maintenance. Unsupported Windows versions require upgrading to receive fixes.

Reference the Microsoft Security Update Guide for technical details. Search for CVE-2026-21535 in the portal. The advisory contains registry-based workarounds for systems that cannot patch immediately. Vulnerability management tools should scan for missing updates.

This marks the third critical Windows RCE flaw patched this quarter. Microsoft attributes discovery to its internal security teams. No bypasses for the patch are currently known.