CVE-2026-32073 - Windows Ancillary Function Driver for WinSock Use-After-Free Vulnerability

CVE-2026-32073 is a critical use-after-free vulnerability affecting the Windows Ancillary Function Driver for WinSock. This vulnerability allows an attacker with local access and low privileges to escalate their privileges to SYSTEM. The vulnerability exists because the driver improperly handles memory allocation, leading to a scenario where freed memory is accessed again. The attacker needs to be authenticated to the system to trigger the vulnerability. As of the publication of this brief, exploitation in the wild has not been observed, but given the potential for privilege escalation, defenders should prioritize patching and detection efforts to mitigate potential risks. This vulnerability was published on 2026-04-14.

Attack Chain

1. Attacker gains initial local access to a Windows system with low privileges.
2. Attacker crafts a malicious application to interact with the Windows Ancillary Function Driver (AFD.sys).
3. The malicious application triggers the use-after-free condition within the AFD driver by sending specially crafted Winsock API calls.
4. The AFD driver attempts to access a memory region that has already been freed.
5. The attacker manipulates the freed memory region to contain malicious data.
6. The driver executes code based on the attacker-controlled content within the freed memory region.
7. This leads to arbitrary code execution within the kernel context.
8. The attacker escalates privileges from their initial low-privileged account to SYSTEM.

Impact

Successful exploitation of CVE-2026-32073 allows a local attacker to escalate their privileges to SYSTEM, granting them complete control over the compromised system. This could lead to sensitive data theft, installation of malware, or disruption of critical services. While the number of potential victims is currently unknown, any Windows system that has not applied the relevant security update is susceptible to this vulnerability. This vulnerability is particularly dangerous in environments where users with limited privileges are common, such as shared workstations or cloud-based environments.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-32073 on all affected Windows systems immediately.
• Monitor system logs for unusual activity related to Winsock API calls, specifically those originating from untrusted or unusual processes using the provided Sigma rule DetectSuspiciousWinsockActivity.
• Enable and review Windows Security Auditing logs for events related to process creation and privilege escalation attempts.
• Consider implementing application control solutions to restrict the execution of unauthorized or untrusted applications.
• Deploy the Sigma rule DetectAFDDriverAccess to identify processes interacting with AFD.sys.