CVE-2014-4113

What Is Win32k?

Win32k.sys is the Windows kernel-mode graphics subsystem — the kernel component responsible for managing windows, menus, graphical drawing operations, and user interface objects. Because Win32k runs in kernel mode (ring 0), any exploitable vulnerability in it can be leveraged for full system privilege escalation: an attacker who achieves code execution at user mode (ring 3) can use a Win32k bug to escalate to SYSTEM. Win32k has historically been one of the most exploited Windows kernel components, responsible for dozens of privilege escalation CVEs over the years.

Overview

CVE-2014-4113 is a local privilege escalation vulnerability in Windows Win32k.sys, exploited as a zero-day by APT groups in October 2014. Discovered by CrowdStrike during investigation of targeted attacks, it was used as the second stage in exploit chains: a remote code execution vulnerability (browser, Flash, Office document) achieves initial code execution at user privilege, then CVE-2014-4113 escalates that access to SYSTEM. Patched in MS14-058 (October 14, 2014) alongside CVE-2014-4148 (TrueType font RCE).

Affected Versions

Fixed in MS14-058 (October 14, 2014).

Technical Details

Root Cause: Use-After-Free in Win32k Object Handling

CVE-2014-4113 is a use-after-free in Win32k.sys. The vulnerability is triggered through specific sequences of user-mode calls to the Win32k window management subsystem — crafted window message processing or object manipulation causes the kernel to use a freed object pointer. Because Win32k operates in kernel space, the use-after-free occurs there, allowing an attacker to write controlled data to kernel memory and redirect kernel execution.

The exploit typically works by:

1. Triggering the use-after-free to corrupt a kernel object (e.g., a window or menu object)
2. Using other Win32k calls to shape the freed memory region with attacker-controlled data
3. Overwriting a function pointer or security token in kernel memory
4. Replacing the calling process's security token with the SYSTEM token

This escalates the attacker's process from low-privilege user to SYSTEM-level, bypassing UAC and all user-mode security controls.

As Part of an Exploit Chain

CVE-2014-4113 was deployed paired with remote code execution exploits (browser zero-days, Flash exploits, or Office document vulnerabilities) in a two-stage chain:

• Stage 1: RCE vulnerability gives initial code execution in a sandboxed or low-privilege context
• Stage 2: CVE-2014-4113 escalates that low-privilege code execution to SYSTEM, enabling full system compromise

Attack Characteristics

Discovery

CrowdStrike discovered active exploitation in the wild during investigation of targeted attacks against organizations in multiple sectors. CrowdStrike reported both CVE-2014-4113 and CVE-2014-4148 to Microsoft simultaneously, as both were being used together. Microsoft released MS14-058 on October 14, 2014.

Exploitation Context

• Zero-day in targeted attacks: Used by APT groups (attributed to China-linked threat actors by CrowdStrike) in targeted spear-phishing and watering-hole campaigns against defense, government, and technology sector organizations
• Paired with CVE-2014-4148: The two MS14-058 vulnerabilities were discovered in the same campaign, often used together — CVE-2014-4148 for initial remote code execution via malicious font in Office documents, CVE-2014-4113 for privilege escalation to SYSTEM
• Exploit chain completion: Win32k LPEs like this are valuable precisely because they complete the chain — a browser or document exploit that gives code execution in a sandbox, combined with a kernel LPE, gives full system access
• CISA KEV (2022): Added May 2022, confirming continued exploitation of this vulnerability class in attacks against unpatched systems

Remediation

1. Apply MS14-058 (October 2014). This bulletin addresses both CVE-2014-4113 (Win32k LPE) and CVE-2014-4148 (TrueType font RCE).

2. Keep Windows fully patched — Win32k privilege escalation vulnerabilities are a recurring class; staying current on Windows updates is essential.

3. Reduce attack surface: Enable application whitelisting (AppLocker, Windows Defender Application Control) to prevent unauthorized code from running and triggering kernel exploits.

4. Enable Windows Defender Exploit Guard / EMET on legacy systems for additional kernel exploit mitigations (Kernel CFG, SMEP enforcement).

5. Internet Explorer retirement: Remove or disable Internet Explorer — the browser that was most commonly paired with Win32k LPEs for exploit chain delivery.