Critical Microsoft Vulnerability CVE-2026-21512 Exposes Systems to Remote Attacks

A critical security vulnerability tracked as CVE-2026-21512 affects multiple Microsoft products. Attackers exploit this flaw remotely without user interaction. Successful compromises grant full system control.

Affected versions include Windows 11 versions 21H2 through 23H2, Windows Server 2022, and Azure Stack Edge devices. The vulnerability resides in the Windows Remote Procedure Call (RPC) subsystem. Specifically, improper memory handling allows arbitrary code execution.

Microsoft assigned a CVSS v3.1 score of 9.8 (Critical). This severity reflects low attack complexity and network-based exploitation vectors. Systems without perimeter defenses face immediate risk.

Mitigation requires installing the July 2026 Patch Tuesday updates through Windows Update. Administrators should prioritize systems exposed to untrusted networks. Apply patches within 24 hours for internet-facing assets.

Microsoft confirmed active exploitation attempts detected since June 15, 2026. No viable workarounds exist beyond patching. Enable Windows Defender Attack Surface Reduction rules as secondary protection.

Review the Security Update Guide entry for technical details. Verify patch deployment using Microsoft's PSWindowsUpdate module. Audit systems using Get-Hotfix -Id KB5028253.

This vulnerability shares similarities with 2022's PetitPotam attacks. It underscores persistent RPC protocol risks. Segment critical networks and monitor for svchost.exe spawning unexpected child processes.