Windows AFD.sys Privilege Escalation: Inside CVE-2025-49661's Untrusted Pointer Dereference

Introduction

Kernel-level vulnerabilities are particularly insidious, granting attackers the keys to the kingdom—complete system control. CVE-2025-49661, an untrusted pointer dereference flaw in Windows Ancillary Function Driver for WinSock (AFD.sys), exemplifies this threat. With a high CVSS score of 7.8, this vulnerability allows authenticated attackers to escalate privileges to SYSTEM level, posing severe risks to enterprise environments.

Technical Information

CVE-2025-49661 is classified under CWE-822, an untrusted pointer dereference issue. The vulnerability resides within the Windows Ancillary Function Driver for WinSock (AFD.sys), a kernel-mode component responsible for managing Winsock API operations. The flaw occurs due to inadequate validation of pointers received from user-mode applications before dereferencing them in kernel space.

Attack Vector and Exploitation Method:

An attacker with local access can exploit this vulnerability by sending maliciously crafted IOCTL requests via Winsock APIs. Specifically, the exploitation targets the driver's handling of socket descriptor metadata, triggering the untrusted pointer dereference. This improper pointer handling leads to kernel memory corruption, enabling arbitrary code execution at the kernel level. Successful exploitation grants the attacker SYSTEM privileges, effectively bypassing all user-mode security mechanisms.

Patch Information

Microsoft has addressed the untrusted pointer dereference vulnerability in the Windows Ancillary Function Driver for WinSock (CVE-2025-49661) by releasing a security update as part of their July 2025 Patch Tuesday. This update modifies the driver's code to ensure pointers are properly validated before dereferencing, thereby preventing potential elevation of privilege attacks. Users are strongly encouraged to apply this update promptly to secure their systems against this vulnerability.

Affected Systems and Versions

Windows 10 (All supported versions)
Windows 11 (All supported versions)
Windows Server 2016 through Windows Server 2025 (All supported versions)

Vendor Security History

Microsoft has previously faced similar vulnerabilities within the AFD.sys driver, notably CVE-2023-21768, which also involved kernel-level memory safety issues. The recurring nature of these vulnerabilities underscores the ongoing challenges Microsoft faces in securing legacy kernel components. However, Microsoft's consistent and timely patching response demonstrates a robust security posture and commitment to addressing critical vulnerabilities promptly.

References

Organizations are advised to prioritize patching immediately and maintain vigilance for potential exploitation attempts.

Source: This report was created using AI

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