CVE-2026-41088: Windows Ancillary Function Driver for WinSock Local Privilege Escalation

CVE-2026-41088 is a local privilege escalation vulnerability affecting the Windows Ancillary Function Driver for WinSock. The vulnerability stems from external control of a file name or path, allowing an authorized local attacker to gain elevated privileges on the system. This vulnerability was published on May 12, 2026. An attacker with local access to a vulnerable system could exploit this vulnerability to execute arbitrary code with elevated privileges, potentially leading to complete system compromise. Defenders should apply the patch released by Microsoft to mitigate this risk.

Attack Chain

1. Attacker gains initial local access to the target Windows system with limited privileges through legitimate means or prior compromise.
2. Attacker crafts a malicious file path or name, taking advantage of the external control vulnerability in the Windows Ancillary Function Driver for WinSock.
3. Attacker triggers a function within the WinSock driver that uses the attacker-controlled file path.
4. The WinSock driver attempts to access or manipulate the file specified by the attacker-controlled path.
5. Due to the lack of proper validation, the driver performs an operation on a file or directory outside of the intended scope.
6. This leads to arbitrary code execution, file overwrite, or other malicious actions.
7. The attacker leverages this arbitrary code execution to inject code into a privileged process or escalate their own process privileges.
8. The attacker achieves elevated privileges, gaining control over the system and potentially performing actions such as installing malware, stealing sensitive data, or creating new administrative accounts.

Impact

Successful exploitation of CVE-2026-41088 allows a local attacker to escalate their privileges to SYSTEM level. This can lead to complete compromise of the affected system. The attacker could install programs, view, change, or delete data, or create new accounts with full user rights. This vulnerability poses a significant risk to systems where unauthorized local access is possible, such as shared workstations or systems with weak access controls.

Recommendation

• Apply the security update provided by Microsoft to address CVE-2026-41088 as detailed in the Microsoft Security Response Center advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41088).
• Implement the Sigma rule “Detect WinSock Driver Exploitation via File Path Manipulation” to detect suspicious process creations or file access patterns indicative of exploitation attempts.
• Monitor for unexpected file creations or modifications in sensitive system directories that may be related to privilege escalation attempts.