CVE-2016-0040

What Is the Windows Kernel?

The Windows kernel (ntoskrnl.exe) is the core of the operating system, running in privileged ring 0 (kernel mode) with unrestricted access to hardware and system resources. Vulnerabilities in kernel components that can be triggered by user-space code represent the most severe class of local privilege escalation — a successful kernel LPE enables an attacker to elevate to SYSTEM, the highest privilege level on Windows, bypassing all user-space security controls, endpoint protection, and access restrictions.

Overview

CVE-2016-0040 is a local privilege escalation vulnerability in the Windows kernel that allows local users to gain SYSTEM-level privileges via a specially crafted application. The vulnerability resides in Windows kernel components and was patched in MS16-014 (February 9, 2016). Like other Windows kernel LPEs, CVE-2016-0040 is used as the second stage in multi-step exploit chains — providing SYSTEM access after an initial foothold is established via browser, document, or network exploitation.

Affected Versions

Fixed in MS16-014 (February 2016). Any Windows system current with Windows Update since February 2016 is protected.

Technical Details

Root Cause: Kernel Privilege Escalation via Crafted Application

CVE-2016-0040 involves a flaw in Windows kernel components where processing a specially crafted application or sequence of system calls triggers a privilege escalation condition. The CVSS PR:N (no privileges required) combined with UI:R (user interaction required) suggests the vulnerability may be triggered when a user opens a crafted file or runs an application that makes specific kernel API calls in an unexpected sequence.

The kernel LPE exploitation pattern:

1. Trigger the kernel vulnerability — the crafted application calls kernel APIs in a sequence that triggers the flaw
2. Kernel pool manipulation — the flaw allows writing to a controlled kernel address
3. Token overwrite — the EPROCESS security token for the attacking process is overwritten with the SYSTEM token
4. SYSTEM privileges achieved — the process now runs with full SYSTEM access

Role in Attack Chains

CVE-2016-0040 serves as the privilege escalation component in multi-stage attack chains:

• Stage 1 — initial code execution at user privilege via browser exploit, email attachment, or exploit kit
• Stage 2 — CVE-2016-0040 escalates from standard user to SYSTEM
• Post-exploitation — with SYSTEM: disable antivirus, install persistence mechanisms, access all files, move laterally

Attack Characteristics

Discovery

Reported to Microsoft and patched in MS16-014 (February 2016 Patch Tuesday).

Exploitation Context

• Post-exploitation escalation: CVE-2016-0040 was used by threat actors requiring SYSTEM privileges following initial access; from SYSTEM, attackers can disable endpoint detection, modify protected system files, create privileged persistence, and access all user data on the compromised system
• Long exploitation tail: CISA's March 2022 KEV addition — six years after the patch — confirms continued exploitation against unpatched Windows systems; Windows 7 and Server 2008 systems that remained in production after EOL (January 2020) were common targets
• CISA KEV (2022): Added March 2022

Remediation

1. Apply MS16-014 (February 2016). Any Windows system current with Windows Update after February 2016 includes this fix.

2. Upgrade end-of-life Windows — Windows 7 and Server 2008 are end-of-life and cannot receive further security updates. Upgrade to Windows 10/11 or Server 2019/2022.

3. Enable Virtualization Based Security (VBS) / HVCI — Hypervisor-Protected Code Integrity significantly raises the bar for kernel exploitation on Windows 10 and later.

4. Principle of least privilege — run user accounts with standard (non-admin) privileges; limit the post-LPE value by ensuring standard users have access only to what they need.