Windows Ancillary Function Driver for WinSock — CraftedSignal Threat Feed

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

hello@craftedsignal.io — Tue, 12 May 2026 18:50:58 +0000

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

Attacker gains initial local access to the target Windows system with limited privileges through legitimate means or prior compromise.
Attacker crafts a malicious file path or name, taking advantage of the external control vulnerability in the Windows Ancillary Function Driver for WinSock.
Attacker triggers a function within the WinSock driver that uses the attacker-controlled file path.
The WinSock driver attempts to access or manipulate the file specified by the attacker-controlled path.
Due to the lack of proper validation, the driver performs an operation on a file or directory outside of the intended scope.
This leads to arbitrary code execution, file overwrite, or other malicious actions.
The attacker leverages this arbitrary code execution to inject code into a privileged process or escalate their own process privileges.
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.

CVE-2026-35416 - Windows Ancillary Function Driver for WinSock Use-After-Free Vulnerability

hello@craftedsignal.io — Tue, 12 May 2026 18:30:35 +0000

CVE-2026-35416 is a use-after-free vulnerability residing within the Windows Ancillary Function Driver for WinSock. This vulnerability allows an attacker, who has already gained authorized access to a local system, to escalate their privileges. The vulnerability stems from improper memory management within the driver, leading to a situation where an attacker can potentially manipulate freed memory to execute arbitrary code with elevated privileges. Successfully exploiting this vulnerability allows a local attacker to gain SYSTEM level privileges.

Attack Chain

Attacker gains initial access to the target Windows system with limited privileges.
Attacker crafts a malicious application to interact with the Windows Ancillary Function Driver for WinSock.
The malicious application triggers the use-after-free condition by improperly freeing a memory object while still holding a reference to it.
The attacker allocates new memory at the same address that was previously freed.
The Windows Ancillary Function Driver attempts to access the originally freed memory, now containing attacker-controlled data.
This access corrupts the driver’s internal state, allowing the attacker to hijack the control flow.
The attacker injects malicious code into the driver’s process.
The injected code executes with elevated (SYSTEM) privileges.

Impact

Successful exploitation of CVE-2026-35416 allows a local attacker to elevate their privileges to SYSTEM. This grants the attacker complete control over the compromised system, enabling them to install software, modify data, and create new accounts with full administrative rights. Given the nature of the vulnerability, any Windows system utilizing the affected driver is susceptible, potentially impacting a broad range of users and organizations.

Recommendation

Apply the security update provided by Microsoft to patch CVE-2026-35416, as referenced in the advisory URL.
Enable Driver Verifier to detect memory corruption issues and potential use-after-free vulnerabilities during driver development and testing.
Deploy the Sigma rule Detect CVE-2026-35416 Exploitation - WinSock Memory Corruption to identify potential exploitation attempts based on process interaction with the vulnerable driver.

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

hello@craftedsignal.io — Tue, 12 May 2026 18:24:46 +0000

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

An attacker gains local access to a Windows system.
The attacker crafts a malicious application designed to trigger the race condition in the Windows Ancillary Function Driver for WinSock.
The malicious application initiates concurrent operations that access a shared resource.
Due to improper synchronization, the concurrent operations lead to a race condition.
The attacker leverages the race condition to manipulate the state of the driver.
By manipulating the driver’s state, the attacker gains elevated privileges.
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.

CVE-2026-34344 — Windows Ancillary Function Driver for WinSock Type Confusion Vulnerability

hello@craftedsignal.io — Tue, 12 May 2026 18:24:34 +0000

CVE-2026-34344 is a type confusion vulnerability affecting the Windows Ancillary Function Driver for WinSock. This vulnerability allows an authorized, local attacker to elevate their privileges on the system. The vulnerability arises from the driver’s handling of resources with incompatible types, leading to a potential privilege escalation. Microsoft has acknowledged the vulnerability and assigned it a CVSS v3.1 score of 7.8, indicating a high severity. Exploitation of this vulnerability requires an attacker to have existing access to the local system.

Attack Chain

The attacker gains initial access to the system with limited privileges.
The attacker crafts a malicious request targeting the Windows Ancillary Function Driver for WinSock.
The request exploits the type confusion vulnerability (CVE-2026-34344) when the driver attempts to access a resource using an incompatible type.
This type confusion allows the attacker to overwrite critical memory locations within the driver’s address space.
The attacker leverages the memory corruption to inject malicious code into the driver’s process.
The injected code executes with the elevated privileges of the Windows Ancillary Function Driver.
The attacker uses the elevated privileges to perform unauthorized actions on the system, such as installing software or modifying system settings.

Impact

Successful exploitation of CVE-2026-34344 allows an attacker to elevate their privileges from a standard user to a higher privileged account, potentially SYSTEM. This could lead to a complete compromise of the affected system, allowing the attacker to install malicious software, modify system data, or create new accounts with administrative rights. The vulnerability affects systems running the Windows Ancillary Function Driver for WinSock.

Recommendation

Apply the security update released by Microsoft to patch CVE-2026-34344; see the advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-34344.
Deploy the Sigma rules in this brief to your SIEM and tune for your environment.