CVE-2026-34345 - Windows Ancillary Function Driver for WinSock Race Condition Privilege Escalation

CVE-2026-34345 is a security vulnerability affecting the Windows Ancillary Function Driver for WinSock. This vulnerability stems from a race condition during concurrent execution while using shared resources. An authorized local attacker can exploit this flaw to elevate their privileges on the system. The vulnerability was published on May 12, 2026, and is documented by Microsoft. Successful exploitation could lead to unauthorized access and control over the affected system, posing a significant risk to confidentiality, integrity, and availability.

Attack Chain

1. An attacker gains local access to a Windows system.
2. The attacker crafts a malicious application designed to trigger the race condition in the Windows Ancillary Function Driver for WinSock.
3. The malicious application initiates concurrent operations that access a shared resource.
4. Due to improper synchronization, the concurrent operations lead to a race condition.
5. The attacker leverages the race condition to manipulate the state of the driver.
6. By manipulating the driver’s state, the attacker gains elevated privileges.
7. The attacker can now execute arbitrary code with elevated privileges.

Impact

Successful exploitation of CVE-2026-34345 allows a local attacker to elevate privileges on the targeted Windows system. This could lead to unauthorized access to sensitive data, modification of system configurations, and installation of malicious software. The impact is significant as it allows a standard user to gain administrative control over the system.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-34345, as referenced in the advisory URL.
• Monitor process creation events for unusual processes spawned by the Ancillary Function Driver using the provided Sigma rule.
• Implement the second Sigma rule to detect potential attempts to exploit the race condition by monitoring for specific API calls related to WinSock.