Heap-Based Buffer Overflow in Microsoft Windows Ancillary Function Driver for WinSock (CVE‑2025‑21418) Enables Local Privilege Escalation
What It Is – The Ancillary Function Driver for WinSock (AFD) in Microsoft Windows contains a heap‑based buffer overflow that can be triggered by a local attacker. Successful exploitation grants the attacker SYSTEM‑level privileges.
Exploitability – The vulnerability is exploitable locally; a proof‑of‑concept exists. Microsoft has issued a security advisory and a patch. CVSS v3.1 base score is 7.8 (High).
Affected Products – All supported versions of Microsoft Windows that include the AFD driver (e.g., Windows 10, Windows Server 2019/2022).
Why It Matters for Trust & Control Assurance
- Access‑control hygiene – Privilege‑escalation flaws undermine the principle of least privilege; continuous monitoring of privileged accounts is essential to detect abuse.
- Patch‑management evidence – Demonstrating timely remediation provides defensible audit evidence for control‑assurance reviews.
- Defensible audit trail – Maintaining logs of patch deployment and privileged‑session activity satisfies multiple control objectives across frameworks (e.g., NIST CSF 2.0, ISO 27001).
Recommended Actions
- Deploy Microsoft’s security update for CVE‑2025‑21418 immediately across all Windows endpoints.
- Verify patch compliance with automated inventory tools and retain evidence of remediation.
- Harden privileged‑account monitoring: enforce least‑privilege policies, enable detailed audit logging, and alert on anomalous SYSTEM‑level activity.
- Conduct a post‑patch validation to ensure the AFD driver no longer permits buffer overflow.
Source: CISA KEV – CVE‑2025‑21418