Microsoft warns of a critical remote code execution flaw in Windows TCP/IP stacks. Unpatched systems risk complete takeover via network attacks.
Microsoft confirms critical security flaw CVE-2026-21521 in Windows operating systems. Attackers can execute malicious code remotely without authentication. This vulnerability impacts core networking components.
Affected versions include Windows 10 21H2/22H2, Windows 11 21H2/22H2, Windows Server 2019, and Windows Server 2022. Unpatched systems face immediate risk. Exploits require no user interaction.
The vulnerability scores 9.8 CVSS v3.1 (Critical). Attack complexity is low. Malicious actors craft IPv6 packets to trigger memory corruption. Successful attacks grant SYSTEM privileges. Compromised systems enable lateral network movement.
Microsoft released patches through May 2026 Security Update. Administrators must apply KB5037789 immediately. Verify installation via command: systeminfo | find "KB5037789".
Temporary mitigation requires disabling IPv6. Use PowerShell: Disable-NetAdapterBinding -Name "*" -ComponentID ms_tcpip6. This reduces functionality. Patching remains the only secure solution.
No active exploitation detected yet. Microsoft credits internal researchers. Similar TCP/IP flaws include CVE-2021-24086. Network segmentation limits attack surface.
Review CVE-2026-21521 details for technical analysis. Prioritize patch deployment within 24 hours. Enterprise environments should validate firewall rules blocking IPv6 at perimeter defenses.
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