Windows Winsock Driver (ws2ifsl.sys) Elevation of Privilege Vulnerability (CVE-2019-1215) Technical Advisory

1. Vulnerability Overview & Root Cause

An elevation of privilege (EoP) vulnerability exists in the Windows Winsock kernel-mode driver, ws2ifsl.sys (Winsock2 Information Service Layer), due to improper handling of objects in memory. The root cause lies in a Use-After-Free (UAF) or reference counting flaw during the lifecycle management of socket-related kernel objects, allowing local attackers to execute arbitrary code within the kernel context.

2. Exploitation Mechanics & Attack Scenario

To exploit this vulnerability, an attacker must first gain local access to the target system with low-privileged user execution rights. The attacker crafts and sends malicious I/O Control (IOCTL) requests to the ws2ifsl.sys driver. By triggering a race condition or manipulating object creation/destruction sequences, the attacker forces the driver to maintain a dangling pointer to a freed socket object. When the attacker fills the freed memory space with controlled shellcode pointers and triggers a reuse of the dangling pointer, the kernel executes the attacker's payload with SYSTEM privileges.

3. Infrastructure & Business Impact

This vulnerability is cataloged in CISA's Known Exploited Vulnerabilities (KEV), indicating active exploitation in the wild. While it requires local access, it is highly critical as a secondary stage in multi-stage attack campaigns (e.g., following an initial web application compromise or phishing vector). Successful exploitation allows attackers to bypass endpoint security controls, establish persistence, dump credentials, and move laterally across the enterprise network.