CriticalCVE-2018-8639

    Microsoft Windows Win32k Improper Resource Shutdown or Release Vulnerability (CVE-2018-8639)

    Published In CISA KEV since Sources: pwn.watch, CVE.org

    What is affected, what to do

    An elevation of privilege vulnerability exists in Windows when the Win32k component fails to properly handle objects in memory, aka "Win32k Elevation of Privilege Vulnerability." This affects Windows 7, Windows Server 2012 R2, Windows RT 8.1, Windows Server 2008, Windows Server 2019, Windows Server 2012, Windows 8.1, Windows Server 2016, Windows Server 2008 R2, Windows 10, Windows 10 Servers. This CVE ID is unique from CVE-2018-8641.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 7 eq 32-bit Systems Service Pack 1..32-bit Systems Service Pack 1
    • Microsoft Windows 7 eq x64-based Systems Service Pack 1..x64-based Systems Service Pack 1
    • Microsoft Windows Server 2012 R2 eq (Server Core installation)..(Server Core installation)
    • Microsoft Windows RT 8.1 eq Windows RT 8.1..Windows RT 8.1
    • Microsoft Windows Server 2008 eq 32-bit Systems Service Pack 2..32-bit Systems Service Pack 2
    • Microsoft Windows Server 2008 eq 32-bit Systems Service Pack 2 (Server Core installation)..32-bit Systems Service Pack 2 (Server Core installation)
    • Microsoft Windows Server 2008 eq Itanium-Based Systems Service Pack 2..Itanium-Based Systems Service Pack 2
    • Microsoft Windows Server 2008 eq x64-based Systems Service Pack 2..x64-based Systems Service Pack 2
    • Microsoft Windows Server 2008 eq x64-based Systems Service Pack 2 (Server Core installation)..x64-based Systems Service Pack 2 (Server Core installation)
    • Microsoft Windows Server 2019 eq (Server Core installation)..(Server Core installation)
    • Microsoft Windows Server 2012 eq (Server Core installation)..(Server Core installation)
    • Microsoft Windows 8.1 eq 32-bit systems..32-bit systems
    • Microsoft Windows 8.1 eq x64-based systems..x64-based systems
    • Microsoft Windows Server 2016 eq (Server Core installation)..(Server Core installation)
    • Microsoft Windows Server 2008 R2 eq Itanium-Based Systems Service Pack 1..Itanium-Based Systems Service Pack 1
    • Microsoft Windows Server 2008 R2 eq x64-based Systems Service Pack 1..x64-based Systems Service Pack 1
    • Microsoft Windows Server 2008 R2 eq x64-based Systems Service Pack 1 (Server Core installation)..x64-based Systems Service Pack 1 (Server Core installation)
    • Microsoft Windows 10 eq 32-bit Systems..32-bit Systems
    • Microsoft Windows 10 eq Version 1607 for 32-bit Systems..Version 1607 for 32-bit Systems
    • Microsoft Windows 10 eq Version 1607 for x64-based Systems..Version 1607 for x64-based Systems
    • Microsoft Windows 10 eq Version 1703 for 32-bit Systems..Version 1703 for 32-bit Systems
    • Microsoft Windows 10 eq Version 1703 for x64-based Systems..Version 1703 for x64-based Systems
    • Microsoft Windows 10 eq Version 1709 for 32-bit Systems..Version 1709 for 32-bit Systems
    • Microsoft Windows 10 eq Version 1709 for ARM64-based Systems..Version 1709 for ARM64-based Systems
    • Microsoft Windows 10 eq Version 1709 for x64-based Systems..Version 1709 for x64-based Systems
    • Microsoft Windows 10 eq Version 1803 for 32-bit Systems..Version 1803 for 32-bit Systems
    • Microsoft Windows 10 eq Version 1803 for ARM64-based Systems..Version 1803 for ARM64-based Systems
    • Microsoft Windows 10 eq Version 1803 for x64-based Systems..Version 1803 for x64-based Systems
    • Microsoft Windows 10 eq Version 1809 for 32-bit Systems..Version 1809 for 32-bit Systems
    • Microsoft Windows 10 eq Version 1809 for ARM64-based Systems..Version 1809 for ARM64-based Systems
    • Microsoft Windows 10 eq Version 1809 for x64-based Systems..Version 1809 for x64-based Systems
    • Microsoft Windows 10 eq x64-based Systems..x64-based Systems
    • Microsoft Windows 10 Servers eq version 1709 (Server Core Installation)..version 1709 (Server Core Installation)
    • Microsoft Windows 10 Servers eq version 1803 (Server Core Installation)..version 1803 (Server Core Installation)

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    8.4

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: pwn.watch, CVE.org

    22.2 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 97.7

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    240.32 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    8.4 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    22.2 %
    Elevated — model estimates 10-50% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    97.7
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 3 March 2025
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-404

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw gives an already logged-on low-privileged user kernel-mode code execution with low complexity and no user interaction. That makes it a textbook second stage after phishing or account compromise. CISA records known use in ransomware campaigns, exploitation likelihood is rated very high, and public exploit code has been available for years. For estates running only supported, fully patched Windows, the risk is low and is closed by a compliance check. It becomes high priority wherever legacy systems (Windows 7/Server 2008, OT operator stations, line-of-business servers) or multi-user hosts lack updates from December 2018 onwards, and in NIS2/KRITIS environments those should be treated as urgent.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Verify patch level and close gaps: Microsoft fixed this vulnerability in the December 2018 security updates (Patch Tuesday). Look up the per-OS KB numbers in the MSRC advisory for CVE-2018-8639. Every current cumulative update includes the fix. Query SCCM/Intune/WSUS for hosts whose last cumulative update predates December 2018 and update them now.
      • Hunt down legacy systems: Windows 7, Windows 8.1, Windows Server 2008/2008 R2 and Windows 10 releases 1507 through 1809 are end-of-life. Confirm the December 2018 update is installed on each. Move hosts that cannot be updated into an isolated segment or decommission them.
      • Patch multi-user hosts first: Terminal servers, RDS/Citrix hosts, VDI pools and jump hosts come first. On these systems, every logged-on user is a potential starting point for privilege escalation.
      • Triage suspected compromise: Use EDR to isolate unpatched hosts that show signs of initial access (phishing, compromised VPN/RDP accounts). Rotate local admin passwords (LAPS) and the credentials of accounts that logged on there. Successful exploitation yields SYSTEM and therefore access to LSASS.
      • Restrict interactive logon: On unpatched servers, use GPO to limit "Allow log on locally" and "Allow log on through Remote Desktop Services" to admin groups only.

    2. Runbook step 2

      Mitigation layers

      • Application control (endpoint hardening): Use WDAC or AppLocker to block execution from user-writable paths (%TEMP%, %APPDATA%, %LOCALAPPDATA%, C:\Users\Public, Downloads). Local exploits are typically dropped there as standalone EXEs or loaded reflectively.
      • Microsoft Defender ASR rules: Set "Block executable files unless they meet a prevalence, age, or trusted list criterion", "Block untrusted and unsigned processes that run from USB" and "Block credential stealing from LSASS" to block mode. The LSASS rule limits what an attacker can do after reaching SYSTEM.
      • IAM/least privilege: Run users without local admin rights and enable Credential Guard and LSA protection (RunAsPPL). Enforce admin tiering so privileged domain accounts never log on to Tier-2 clients, which means local SYSTEM does not translate into domain privileges.
      • Network segmentation: Put unpatchable legacy systems in a dedicated VLAN. Block SMB (445/tcp), RDP (3389/tcp) and WinRM (5985/5986/tcp) to other segments, and allow outbound internet only through an allowlisted proxy. This contains lateral movement after escalation.
      • Raise the cost of initial access: Block internet-sourced macros, enforce MFA on VPN/RDP gateways and filter email attachments. The bug requires code execution in user context, so cutting off the initial vector is the strongest lever.

    3. Runbook step 3

      Detection rules

      • Integrity-level jump in the process chain (EDR/Sysmon EID 1): Look for a process running at System integrity whose parent runs at Medium or Low and is not a known service. KQL: DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel in ("Medium","Low") and InitiatingProcessFileName !in~ ("msiexec.exe","consent.exe")
      • SYSTEM shell spawned from a user path (Windows 4688 / Sysmon EID 1): Watch for cmd.exe or powershell.exe running as S-1-5-18 with a parent image under \Users\*\AppData\* or \Temp\. Sigma shape: Image|endswith: ['\cmd.exe','\powershell.exe'] AND User: 'NT AUTHORITY\SYSTEM' AND ParentImage|contains: ['\AppData\','\Temp\']
      • Failed exploitation attempts: Win32k kernel exploits often crash the host. Flag bugchecks (System log Event ID 1001 BugCheck, Event ID 41 Kernel-Power) that reference win32k.sys/win32kfull.sys on unpatched hosts, especially when they repeat or coincide with suspicious process launches.
      • Post-escalation activity: Watch for service installs (Event ID 7045 / 4697), LSASS access (Sysmon EID 10, TargetImage lsass.exe, GrantedAccess 0x1010/0x1410), shadow copy deletion (vssadmin delete shadows, wmic shadowcopy delete) and Defender being disabled (Event ID 5001). These are classic ransomware precursors.
      • Token manipulation: Treat EDR alerts for token theft or kernel token swapping as high severity. Win32k exploitation usually ends by overwriting the process token with the SYSTEM token.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    An elevation of privilege vulnerability exists in Windows when the Win32k component fails to properly handle objects in memory, aka "Win32k Elevation of Privilege Vulnerability." This affects Windows 7, Windows Server 2012 R2, Windows RT 8.1, Windows Server 2008, Windows Server 2019, Windows Server 2012, Windows 8.1, Windows Server 2016, Windows Server 2008 R2, Windows 10, Windows 10 Servers. This CVE ID is unique from CVE-2018-8641.

    Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    MicrosoftWindows 10
    • Version 1809 for x64-based Systems
    • 32-bit Systems
    • Version 1803 for 32-bit Systems
    • Version 1809 for ARM64-based Systems
    • x64-based Systems
    • Version 1703 for 32-bit Systems
    • Version 1803 for ARM64-based Systems
    • Version 1809 for 32-bit Systems
    • Version 1709 for 32-bit Systems
    • Version 1803 for x64-based Systems
    • Version 1709 for ARM64-based Systems
    • Version 1607 for 32-bit Systems
    • Version 1703 for x64-based Systems
    • Version 1709 for x64-based Systems
    • Version 1607 for x64-based Systems
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    MicrosoftWindows 10 Servers
    • version 1803 (Server Core Installation)
    • version 1709 (Server Core Installation)
    • —
    • —
    MicrosoftWindows 7
    • 32-bit Systems Service Pack 1
    • x64-based Systems Service Pack 1
    • —
    • —
    MicrosoftWindows 8.1
    • x64-based systems
    • 32-bit systems
    • —
    • —
    MicrosoftWindows RT 8.1
    • Windows RT 8.1
    • —
    MicrosoftWindows Server 2008
    • x64-based Systems Service Pack 2 (Server Core installation)
    • 32-bit Systems Service Pack 2 (Server Core installation)
    • 32-bit Systems Service Pack 2
    • x64-based Systems Service Pack 2
    • Itanium-Based Systems Service Pack 2
    • —
    • —
    • —
    • —
    • —
    MicrosoftWindows Server 2008 R2
    • x64-based Systems Service Pack 1
    • Itanium-Based Systems Service Pack 1
    • x64-based Systems Service Pack 1 (Server Core installation)
    • —
    • —
    • —
    MicrosoftWindows Server 2012
    • (Server Core installation)
    • —
    MicrosoftWindows Server 2012 R2
    • (Server Core installation)
    • —
    MicrosoftWindows Server 2016
    • (Server Core installation)
    • —
    MicrosoftWindows Server 2019
    • (Server Core installation)
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_1507—
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_1703—
    Windowsmicrosoftwindows_10_1709—
    Windowsmicrosoftwindows_10_1803—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_7—
    Windowsmicrosoftwindows_8.1—
    Windowsmicrosoftwindows_rt_8.1—
    Windowsmicrosoftwindows_server_2008r2
    Windowsmicrosoftwindows_server_2008—
    Windowsmicrosoftwindows_server_2012r2
    Windowsmicrosoftwindows_server_2012—
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_2019—

    Weakness classes (CWE)

    • CWE-404Improper Resource Shutdown or Release

      Class

      The product does not release or incorrectly releases a resource before it is made available for re-use.

      Entry at MITRE CWE-404

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • securityfocus.com106093Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
    • portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2018-8639x_refsource_CONFIRM, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2018-8639government-resource, US government resource
    • pwn.watchpwn.watch: Microsoft Windows: Windows Win32k Improper Resource Shutdown or Release Vulnerabilitypwn-watch
    • Microsoft Security Update GuideMicrosoft advisory: Microsoft Windowspwn-watch
    • NVD (NIST)NVD: CVE-2018-8639pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2018-8639
    <a href="https://intel.neosec.eu/en/cve/CVE-2018-8639"><img src="https://intel.neosec.eu/badge/cve/CVE-2018-8639.svg?lang=en" alt="CVE-2018-8639 – NEOSEC Intel" height="20"></a>