CVE-2018-8639
Microsoft Windows Win32k Improper Resource Shutdown or Release Vulnerability
Description
CVE-2018-8639 is a high-severity elevation of privilege vulnerability in the Windows Win32k component that occurs when it fails to properly handle objects in memory. An authenticated local attacker can exploit this vulnerability to execute arbitrary code in kernel mode, gaining full control over the affected system. With a CVSS v3.1 base score of 7.8, the vulnerability affects a wide range of Windows versions from Windows 7 through Windows Server 2019. CISA has added CVE-2018-8639 to the Known Exploited Vulnerabilities catalog with a remediation deadline of March 24, 2025, and it is known to be used in ransomware campaigns. The EPSS score of 31.88% at the 97th percentile confirms significant ongoing exploitation activity.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | - |
| microsoft | windows 10 1607 | - |
| microsoft | windows 10 1703 | - |
| microsoft | windows 10 1709 | - |
| microsoft | windows 10 1803 | - |
| microsoft | windows 10 1809 | - |
| microsoft | windows 7 | - |
| microsoft | windows 8.1 | - |
| microsoft | windows rt 8.1 | - |
| microsoft | windows server 2008 | -; r2 |
| microsoft | windows server 2012 | -; r2 |
| microsoft | windows server 2016 | - |
| microsoft | windows server 2019 | - |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- http://www.securityfocus.com/bid/106093(Broken Link, Third Party Advisory, VDB Entry)
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-8639(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2018-8639(US Government Resource)
Weakness Type
Win32k Improper Object Handling
CVE-2018-8639 results from improper handling of objects in memory by the Win32k kernel-mode driver. The Win32k component is responsible for managing the Windows graphical subsystem, including window management, screen output, and input processing. When Win32k fails to correctly manage object lifetimes or reference counts in memory, an attacker can manipulate these objects to achieve a use-after-free or similar memory corruption condition, ultimately enabling kernel-mode code execution. This vulnerability class is closely related to CWE-416 (Use After Free) and CWE-269 (Improper Privilege Management).
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2018-8639 poses a serious threat to organizations running legacy and currently supported Windows systems. The vulnerability requires local access (AV:L) with low attack complexity (AC:L) and low privileges (PR:L), requiring no user interaction (UI:N). Confidentiality (High): Kernel-mode code execution grants the attacker access to all system memory, including credentials, encryption keys, and data from all user sessions. The attacker can read any file on the system regardless of access control lists. Integrity (High): With kernel-level access, the attacker can modify any system file, install rootkits, disable security software, and alter audit logs to cover tracks. Availability (High): Kernel-mode access allows the attacker to crash the system, corrupt the file system, or deploy ransomware with maximum impact. The confirmed association with ransomware campaigns makes this vulnerability particularly dangerous. The EPSS score of 31.88% at the 97th percentile indicates that this seven-year-old vulnerability continues to be actively targeted, especially against systems running unpatched legacy Windows versions such as Windows 7 and Windows Server 2008 that may no longer receive security updates.
Exploit Maturity
CVE-2018-8639 demonstrates sustained long-term exploitation with confirmed ransomware use. CISA has added this vulnerability to the Known Exploited Vulnerabilities catalog and has explicitly confirmed its use in ransomware campaigns, highlighting its continued relevance years after disclosure. The EPSS score of 31.88% at the 97th percentile reflects significant ongoing exploitation activity. Microsoft published a security advisory and patches in December 2018, yet the vulnerability remains actively targeted against unpatched systems. The Win32k component has historically been one of the most frequently exploited attack surfaces in Windows, and CVE-2018-8639 continues this pattern. The vulnerability is particularly valuable to attackers as a local privilege escalation primitive, commonly chained with initial access vectors such as phishing or web exploitation to achieve full system compromise.
Remediation
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Apply Microsoft security updates immediately. Microsoft released patches for CVE-2018-8639 as part of the December 2018 security updates. Apply the update from the Microsoft Security Response Center advisory to all affected systems including Windows 7, 8.1, 10, Server 2008, 2012, 2016, and 2019.
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Upgrade end-of-life Windows versions. Windows 7, Windows Server 2008, and Windows Server 2008 R2 have reached end of life and may not receive security updates. Migrate these systems to supported Windows versions (Windows 10/11 or Windows Server 2019/2022) to ensure ongoing security patch availability.
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Implement application whitelisting and exploit mitigation. Deploy Windows Defender Exploit Guard or similar exploit mitigation tools that can detect and block Win32k exploitation techniques. Enable Attack Surface Reduction (ASR) rules to limit the ability of applications to interact with the Win32k subsystem in exploitable ways.
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Restrict local access and enforce least privilege. Since the vulnerability requires local access with low privileges, minimize the number of users with interactive login capabilities on servers. Implement strict group policy settings to limit local administrative access and use Privileged Access Management solutions.
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Deploy endpoint detection and response (EDR) solutions. Configure EDR tools to monitor for Win32k exploitation indicators, including suspicious system call patterns, unexpected kernel-mode transitions from user-space applications, and privilege escalation attempts. Given the confirmed ransomware association, ensure ransomware-specific detection rules are active and anti-tamper protections are enabled.
Technical Details
CVE-2018-8639 is an elevation of privilege vulnerability in the Win32k kernel-mode driver, a core component of the Windows graphical subsystem. The CVSS v3.1 vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H indicates local access with low privileges and complexity, achieving maximum impact across confidentiality, integrity, and availability within the same security scope. The Win32k driver handles window management, display rendering, and input processing in kernel mode. The vulnerability occurs when Win32k fails to properly manage object lifetimes in memory — specifically, objects related to window management can be freed prematurely while still referenced, or reference counts can be manipulated to cause memory corruption. An attacker running a specially crafted application can trigger this improper object handling to corrupt kernel memory structures, overwriting function pointers or other control data to redirect kernel execution flow. The result is arbitrary code execution in kernel mode (Ring 0), which provides complete control over the operating system. This class of Win32k vulnerability has been repeatedly targeted because the component runs in kernel mode, processes complex user-controllable input, and has a large attack surface. The broad range of affected Windows versions — from Windows 7 and Server 2008 through Windows 10 and Server 2019 — reflects the shared Win32k codebase across the Windows product family.
Frequently Asked Questions
Is CVE-2018-8639 being used in ransomware attacks?
Yes. CISA has explicitly confirmed that CVE-2018-8639 is known to be used in ransomware campaigns. Attackers use this local privilege escalation vulnerability to gain kernel-level access after initial compromise, enabling them to disable security tools and deploy ransomware with maximum impact across the affected system.
What Windows versions are affected by CVE-2018-8639?
CVE-2018-8639 affects a broad range of Windows versions including Windows 7, Windows 8.1, Windows RT 8.1, Windows 10 (versions 1507 through 1809), Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, Windows Server 2016, and Windows Server 2019.
How do I fix CVE-2018-8639?
Apply the December 2018 security updates from Microsoft through Windows Update or the Microsoft Security Response Center advisory page. For end-of-life Windows versions (Windows 7, Server 2008), upgrading to a supported Windows version is strongly recommended as these systems may not continue to receive security patches.
Why is a 2018 vulnerability still being actively exploited?
CVE-2018-8639 continues to be exploited because many organizations still run unpatched legacy Windows systems, particularly Windows 7 and Windows Server 2008. The vulnerability provides reliable kernel-level privilege escalation with low complexity, making it a valuable tool in attack chains. Win32k vulnerabilities are among the most commonly exploited Windows kernel flaws due to the component's large attack surface.
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