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

CVE-2025-21418 is a critical elevation of privilege (EoP) vulnerability identified in the Windows Ancillary Function Driver for WinSock (AFD.sys). This driver serves as a kernel-mode component that facilitates communication between Windows applications and the internet by interfacing with the Windows Sockets API. An authenticated attacker can exploit this vulnerability by executing a specially crafted program, allowing them to run code with SYSTEM-level privileges. Notably, this flaw has been actively exploited in the wild, underscoring its severity.

What is Vulnerable to CVE-2025-21418

The vulnerability affects multiple versions of Microsoft Windows, including:

• Windows 10
• Windows 11
• Windows Server 2008 SP2
• Windows Server 2008 R2
• Windows Server 2012
• Windows Server 2012 R2
• Windows Server 2016
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025
• Windows Server 23h2

The widespread nature of this vulnerability means a significant number of systems are potentially at risk.

Mitigation and Remediation for CVE-2025-21418

Microsoft has released an official patch to address CVE-2025-21418 as part of its February 2025 Patch Tuesday updates. It is imperative for organizations and individuals to apply this patch promptly to mitigate potential exploitation. In addition to patching, consider the following best practices:

• Principle of Least Privilege: Ensure users have only the necessary privileges to perform their tasks, reducing the potential impact of exploitation.
• Application Whitelisting: Permit only approved applications to run, preventing unauthorized code execution.
• System Monitoring: Continuously monitor systems for unusual activities, especially those related to privilege escalation attempts.

Implementing these measures alongside the official patch enhances the security posture against potential threats.

Impact of Successful Exploitation of CVE-2025-21418

Exploiting this vulnerability allows attackers to:

• Gain SYSTEM-Level Privileges: Achieve the highest level of access on the affected system.
• Disable Security Tools: Potentially turn off antivirus and other security measures.
• Access Sensitive Data: View or exfiltrate confidential information.
• Move Laterally: Navigate within the network to compromise additional systems.

The high CVSS v3.1 base score of 7.8 reflects the significant risk associated with this vulnerability.

Proof of Concept for CVE-2025-21418

As of now, there is no publicly available proof-of-concept (PoC) exploit for CVE-2025-21418. However, given the nature of the vulnerability, it’s plausible that threat actors could develop and utilize such exploits. Organizations should proactively implement the recommended mitigations and prioritize applying the official patch to safeguard against potential exploitation.

For further details and updates, refer to Microsoft’s official security advisory.