CriticalCVE-2021-31979

    Windows Kernel Elevation of Privilege Vulnerability (CVE-2021-31979)

    Published Last modified In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Windows Kernel Elevation of Privilege Vulnerability

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1507 to version 10.0.10240.19003, Microsoft Windows 10 Version 1607 to version 10.0.14393.4530, Microsoft Windows 10 Version 1809 to version 10.0.17763.2061. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.19003
    • Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.4530
    • Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.2061
    • Microsoft Windows 10 Version 1909 lt 10.0.0..10.0.18363.1679
    • Microsoft Windows 10 Version 2004 lt 10.0.0..10.0.19041.1110
    • Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.1110
    • Microsoft Windows 10 Version 21H1 lt 10.0.0..10.0.19043.1110
    • Microsoft Windows 7 lt 6.1.0..6.1.7601.25661
    • Microsoft Windows 7 Service Pack 1 lt 6.1.0..6.1.7601.25661
    • Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20069
    • Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.7601.0..6.1.7601.25661
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.25661
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.21167
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.21167
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.23409
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.23409
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20069
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20069
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.4530
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.4530
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.2061
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.2061
    • Microsoft Windows Server version 2004 lt 10.0.0..10.0.19041.1110
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1110
    Fixed in
    • Microsoft Windows 10 Version 1507 10.0.10240.19003
    • Microsoft Windows 10 Version 1607 10.0.14393.4530
    • Microsoft Windows 10 Version 1809 10.0.17763.2061
    • Microsoft Windows 10 Version 1909 10.0.18363.1679
    • Microsoft Windows 10 Version 2004 10.0.19041.1110
    • Microsoft Windows 10 Version 20H2 10.0.19042.1110
    • Microsoft Windows 10 Version 21H1 10.0.19043.1110
    • Microsoft Windows 7 6.1.7601.25661
    • Microsoft Windows 7 Service Pack 1 6.1.7601.25661
    • Microsoft Windows 8.1 6.3.9600.20069
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25661
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25661
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21167
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21167
    • Microsoft Windows Server 2012 6.2.9200.23409
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23409
    • Microsoft Windows Server 2012 R2 6.3.9600.20069
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20069
    • Microsoft Windows Server 2016 10.0.14393.4530
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.4530
    • Microsoft Windows Server 2019 10.0.17763.2061
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2061
    • Microsoft Windows Server version 2004 10.0.19041.1110
    • Microsoft Windows Server version 20H2 10.0.19042.1110

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

    Metrics

    7.8

    Priority

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

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    4.5 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 91.5

    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
    206.02 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
    7.8 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
    4.5 %
    Moderate — model estimates 1-10% 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
    91.5
    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 4 March 2024
    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-119

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This is a low-complexity local kernel attack path that needs only low privileges and no user interaction, and it grants full compromise of confidentiality, integrity and availability — it was used as a zero-day inside exploit chains to escalate from a user context to SYSTEM. Exploitation likelihood is well above average, while CISA reports no known use in ransomware campaigns. Since the fix has been available since July 2021, any remaining hits mostly point to forgotten legacy assets; rate them high, especially on multi-user systems (RDS, VDI) or admin workstations, and treat them as evidence of wider patch-management gaps relevant to NIS2 Art. 21.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory patch level: Compare every Windows endpoint against the fixed builds. Anything below these is vulnerable: 1507 → 10.0.10240.19003, 1607 → 10.0.14393.4530, 1809 → 10.0.17763.2061, 1909 → 10.0.18363.1679, 2004/20H2/21H1 → 10.0.19041/19042/19043.1110, Windows 7 → 6.1.7601.25661. Quick check in MDE: DeviceTvmSoftwareVulnerabilities | where CveId == "CVE-2021-31979".
      • Deploy the security update: Push the Microsoft cumulative update that brings hosts to the builds above (or any later cumulative update) via WSUS/Intune/SCCM. Look up the exact KB per version in the Microsoft Security Update Guide. Force a reboot — kernel fixes only take effect after restart.
      • Handle Windows 7 separately: The 6.1.7601.25661 fix requires an active ESU subscription. Treat hosts without ESU as unpatchable: isolate them and schedule migration. The same applies to out-of-support Windows 10 releases (1507, 1909, 2004, etc.).
      • Check server kernels too: Windows Server shares its kernel base with the listed client releases (e.g. 1607/1809). Confirm affected Server SKUs in the vendor advisory and don't let server patching trail behind clients.
      • Patch high-value targets first: Privileged access workstations, jump hosts, RDS/terminal servers and VDI pools — local privilege escalation there leads straight to privileged credentials.

    2. Runbook step 2

      Mitigation layers

      • Block initial access (primary defence): Exploitation needs low-privileged local code execution. Keep browsers and Office current — kernel EoP bugs like this are typically the second stage after a browser or document exploit.
      • Application control: WDAC or AppLocker in enforcement mode for user-writable paths (%TEMP%, %APPDATA%, Downloads) to stop standard users from dropping and running exploit binaries.
      • Credential protection: Enable Credential Guard and LSA Protection (RunAsPPL=1) so SYSTEM access doesn't immediately yield LSASS secrets; enable the ASR rule "Block credential stealing from LSASS".
      • Kernel hardening: Turn on HVCI (Memory Integrity) and the Microsoft Vulnerable Driver Blocklist to make kernel-level persistence harder after a successful exploit.
      • Least privilege and segmentation: No local admin for standard users, LAPS for local admin accounts; move unpatchable legacy hosts (Windows 7 without ESU) into a dedicated VLAN with no path to AD Tier 0 and no internet egress.

    3. Runbook step 3

      Detection rules

      • Integrity jump (Sysmon EID 1 / Security 4688): Process running as NT AUTHORITY\SYSTEM / IntegrityLevel: System whose parent runs as a standard user at Medium integrity. KQL sketch: DeviceProcessEvents | where AccountSid == "S-1-5-18" and InitiatingProcessAccountSid != "S-1-5-18" and InitiatingProcessFileName !in~ ("services.exe","svchost.exe","wininit.exe").
      • Suspicious process ancestry (EDR): chrome.exe/msedge.exe/winword.exe → cmd.exe/powershell.exe/rundll32.exe followed by SYSTEM-level execution; Sigma shape: ParentImage|endswith: browser/office AND IntegrityLevel: System.
      • Kernel instability: Correlate System Event ID 1001 (BugCheck) and 41 (Kernel-Power) plus new MEMORY.DMP/minidumps on workstations — failed kernel exploit attempts frequently cause blue screens.
      • Post-exploitation: Sysmon EID 10 with TargetImage: lsass.exe from an unusual SourceImage, Security 4697/System 7045 (new service), and Sysmon EID 6 (unsigned driver or driver loaded from a user path) shortly after an integrity jump.
      • Patch compliance as a control: Weekly report of hosts below the fixed build; weight alerts from the rules above higher on non-compliant hosts.

    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

    Windows Kernel Elevation of Privilege Vulnerability

    Source: cvelistv5, CISA KEV Catalog, NVD (NIST), 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 1507
    • 10.0.10240.0 – < 10.0.10240.19003
    • 10.0.10240.19003
    MicrosoftWindows 10 Version 1607
    • 10.0.14393.0 – < 10.0.14393.4530
    • 10.0.14393.4530
    MicrosoftWindows 10 Version 1809
    • 10.0.17763.0 – < 10.0.17763.2061
    • 10.0.17763.2061
    MicrosoftWindows 10 Version 1909
    • 10.0.0 – < 10.0.18363.1679
    • 10.0.18363.1679
    MicrosoftWindows 10 Version 2004
    • 10.0.0 – < 10.0.19041.1110
    • 10.0.19041.1110
    MicrosoftWindows 10 Version 20H2
    • 10.0.0 – < 10.0.19042.1110
    • 10.0.19042.1110
    MicrosoftWindows 10 Version 21H1
    • 10.0.0 – < 10.0.19043.1110
    • 10.0.19043.1110
    MicrosoftWindows 7
    • 6.1.0 – < 6.1.7601.25661
    • 6.1.7601.25661
    MicrosoftWindows 7 Service Pack 1
    • 6.1.0 – < 6.1.7601.25661
    • 6.1.7601.25661
    MicrosoftWindows 8.1
    • 6.3.0 – < 6.3.9600.20069
    • 6.3.9600.20069
    MicrosoftWindows Server 2008 R2 Service Pack 1
    • 6.1.7601.0 – < 6.1.7601.25661
    • 6.1.7601.25661
    MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
    • 6.1.7601.0 – < 6.1.7601.25661
    • 6.1.7601.25661
    MicrosoftWindows Server 2008 Service Pack 2
    • 6.0.6003.0 – < 6.0.6003.21167
    • 6.0.6003.21167
    MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
    • 6.0.6003.0 – < 6.0.6003.21167
    • 6.0.6003.21167
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.23409
    • 6.2.9200.23409
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.23409
    • 6.2.9200.23409
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.20069
    • 6.3.9600.20069
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.20069
    • 6.3.9600.20069
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.4530
    • 10.0.14393.4530
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.4530
    • 10.0.14393.4530
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.2061
    • 10.0.17763.2061
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.2061
    • 10.0.17763.2061
    MicrosoftWindows Server version 2004
    • 10.0.0 – < 10.0.19041.1110
    • 10.0.19041.1110
    MicrosoftWindows Server version 20H2
    • 10.0.0 – < 10.0.19042.1110
    • 10.0.19042.1110

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_150710.0.10240.19003
    Windowsmicrosoftwindows_10_1507—
    Windowsmicrosoftwindows_10_160710.0.14393.4530
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_180910.0.17763.2061
    Windowsmicrosoftwindows_10_180910.0.18363.1679
    Windowsmicrosoftwindows_10_180910.0.19041.1110
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_10_190910.0.18363.1679
    Windowsmicrosoftwindows_10_1909—
    Windowsmicrosoftwindows_10_2004—
    Windowsmicrosoftwindows_10_20H210.0.19042.1110
    Windowsmicrosoftwindows_10_20h2—
    Windowsmicrosoftwindows_10_21H110.0.19043.1110
    Windowsmicrosoftwindows_10_21h1—
    Windowsmicrosoftwindows_76.1.7601.25661
    Windowsmicrosoftwindows_7—
    Windowsmicrosoftwindows_8.16.3.9600.20069
    Windowsmicrosoftwindows_8.1—
    Windowsmicrosoftwindows_rt_8.16.3.9600.20069
    Windowsmicrosoftwindows_rt_8.1—
    Windowsmicrosoftwindows_server_200410.0.19041.1110
    Windowsmicrosoftwindows_server_2004—
    Windowsmicrosoftwindows_server_2008r2

    Weakness classes (CWE)

    • CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

      Class

      The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

      Entry at MITRE CWE-119

    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

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. NVD analysis modifiedNVD

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Reference typeadded
      —
      Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31979 Types: Patch, Vendor Advisory

      Source identifier: nvd@nist.gov

    2. Record modifiedMicrosoft

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31979
      Referenceremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31979
      —
      Reference typeremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31979 Types: Patch, Vendor Advisory
      —
      Affected versions (publisher)changed
      Windows 10 Version 1809, Windows Server 2019, Windows Server 2019 (Server Core installation) (+22)
      Windows 10 Version 1507, Windows 10 Version 1607, Windows 10 Version 1809 (+22)

      Source identifier: secure@microsoft.com

    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-2021-31979
    <a href="https://intel.neosec.eu/en/cve/CVE-2021-31979"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-31979.svg?lang=en" alt="CVE-2021-31979 – NEOSEC Intel" height="20"></a>