CVE-2025-21418: Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability

Required action (CISA's text)

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Description (NVD)

Microsoft Windows Ancillary Function Driver for WinSock contains a heap-based buffer overflow vulnerability that allows for privilege escalation, enabling a local attacker to gain SYSTEM privileges.

SOURCES

• CISA KEVCISA Known Exploited Vulnerabilities catalog

Other Microsoft flaws

• patchtuesday:2026-11: Vulnerability in Microsoft
• CVE-2026-124194: Microsoft Office Outlook Missing User Interaction for Potentially Unsafe Action Vulnerability
• CVE-2026-96951: Microsoft Windows Command Injection Vulnerability
• CVE-2026-65660: Microsoft SharePoint Code Injection Vulnerability
• CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability

Data from NVD, CISA KEV, FIRST EPSS and vendor advisories. Updated 10 Nov 2026.