Windows AFD.sys Zero-Day CVE-2025-32709: Exploiting Use-After-Free for SYSTEM Privileges

Introduction

Attackers have been actively exploiting CVE-2025-32709, a critical use-after-free vulnerability in Microsoft's Windows Ancillary Function Driver for WinSock (AFD.sys), to escalate privileges from standard user accounts to full SYSTEM-level access. This flaw has been leveraged in targeted ransomware and APT campaigns, underscoring the urgent need for immediate remediation.

Affected Systems and Versions

The vulnerability specifically impacts the following Windows versions:

• Windows 10 (all editions)
• Windows 11 (all editions)
• Windows Server 2016, 2019, 2022

All versions using the AFD.sys driver prior to the May 2025 security update (KB5034441) are vulnerable.

Technical Information

The use-after-free vulnerability (CWE-416) in AFD.sys occurs due to improper handling of memory after socket closure. Specifically, the driver fails to nullify pointers to freed memory blocks, allowing attackers to reuse these memory locations for malicious purposes.

Vulnerable Code Snippet

NTSTATUS AfdProcessIOCTL(PVOID Context, PIRP Irp) {
    PAFD_CONTEXT afdContext = (PAFD_CONTEXT)Context;
    if (afdContext->State == FREED) {
        // Vulnerable use-after-free condition
        ModifySecurityDescriptor(afdContext->Descriptor);
    }
    return STATUS_SUCCESS;
}

Attackers exploit this vulnerability by sending specially crafted IOCTL requests, causing the driver to reuse freed memory for attacker-controlled data. This manipulation allows overwriting kernel structures and elevating privileges to SYSTEM.

Proof of Concept

Currently, no publicly available proof-of-concept (PoC) exploit exists. The vulnerability details provided are based on reverse-engineering the official Microsoft patch and analysis by security researchers.

Patch Information

Microsoft has released a security update addressing this vulnerability as part of the May 2025 Patch Tuesday:

• Patch ID: KB5034441
• Affected Component: AFD.sys
• Patch Availability: Microsoft Update Catalog

Organizations should apply this patch immediately. No alternative mitigations are currently available.

Detection Methods

Organizations should monitor for the following indicators of potential exploitation:

• Unusual kernel-mode API calls (e.g., NtAllocateVirtualMemory)
• Unexpected process creations, particularly involving administrative tools like cmd.exe or PowerShell from non-interactive sessions
• Suspicious driver load events involving AFD.sys

Vendor Security History

Microsoft has previously addressed similar vulnerabilities in the AFD.sys driver:

• CVE-2025-21418: Another use-after-free vulnerability exploited by ransomware actors in February 2025

Repeated vulnerabilities in this driver indicate ongoing security challenges in legacy kernel components.

References

• Microsoft Security Response Center
• National Vulnerability Database
• CISA Known Exploited Vulnerabilities Catalog

Immediate action is critical to mitigate the risk posed by this actively exploited vulnerability. Security teams should prioritize patching and monitoring to protect their environments from potential exploitation.