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

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

1. Attacker gains initial access to the target Windows system with limited privileges.
2. Attacker crafts a malicious application to interact with the Windows Ancillary Function Driver for WinSock.
3. The malicious application triggers the use-after-free condition by improperly freeing a memory object while still holding a reference to it.
4. The attacker allocates new memory at the same address that was previously freed.
5. The Windows Ancillary Function Driver attempts to access the originally freed memory, now containing attacker-controlled data.
6. This access corrupts the driver’s internal state, allowing the attacker to hijack the control flow.
7. The attacker injects malicious code into the driver’s process.
8. 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.