CriticalCVE-2021-41379

    Windows Installer Elevation of Privilege Vulnerability (CVE-2021-41379)

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

    What is affected, what to do

    Windows Installer Elevation of Privilege Vulnerability

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Microsoft Windows 10 Version 1507 to version 10.0.10240.19119, Microsoft Windows 10 Version 1607 to version 10.0.14393.4770, Microsoft Windows 10 Version 1809 to version 10.0.17763.2300. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.19119
    • Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.4770
    • Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.2300
    • Microsoft Windows 10 Version 1909 lt 10.0.0..10.0.18363.1916
    • Microsoft Windows 10 Version 2004 lt 10.0.0..10.0.19041.1348
    • Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.1348
    • Microsoft Windows 10 Version 21H1 lt 10.0.0..10.0.19043.1348
    • Microsoft Windows 11 version 21H2 lt 10.0.22000.0..10.0.22000.318
    • Microsoft Windows 7 lt 6.1.0..6.1.7601.25769
    • Microsoft Windows 7 Service Pack 1 lt 6.1.0..6.1.7601.25769
    • Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20174
    • Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.7601.0..6.1.7601.25769
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.25769
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.21282
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.21282
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.23517
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.23517
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20174
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20174
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.4770
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.4770
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.2300
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.2300
    • Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.350
    • Microsoft Windows Server version 2004 lt 10.0.0..10.0.19041.1348
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1348
    Fixed in
    • Microsoft Windows 10 Version 1507 10.0.10240.19119
    • Microsoft Windows 10 Version 1607 10.0.14393.4770
    • Microsoft Windows 10 Version 1809 10.0.17763.2300
    • Microsoft Windows 10 Version 1909 10.0.18363.1916
    • Microsoft Windows 10 Version 2004 10.0.19041.1348
    • Microsoft Windows 10 Version 20H2 10.0.19042.1348
    • Microsoft Windows 10 Version 21H1 10.0.19043.1348
    • Microsoft Windows 11 version 21H2 10.0.22000.318
    • Microsoft Windows 7 6.1.7601.25769
    • Microsoft Windows 7 Service Pack 1 6.1.7601.25769
    • Microsoft Windows 8.1 6.3.9600.20174
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25769
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25769
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21282
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21282
    • Microsoft Windows Server 2012 6.2.9200.23517
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23517
    • Microsoft Windows Server 2012 R2 6.3.9600.20174
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20174
    • Microsoft Windows Server 2016 10.0.14393.4770
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.4770
    • Microsoft Windows Server 2019 10.0.17763.2300
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2300
    • Microsoft Windows Server 2022 10.0.20348.350
    • Microsoft Windows Server version 2004 10.0.19041.1348
    • Microsoft Windows Server version 20H2 10.0.19042.1348

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

    Metrics

    5.5

    Priority

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

    Source: NVD, CVSS v3

    5.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org

    19.5 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 97.4

    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
    228.33 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
    5.5 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
    5.5
    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
    19.5 %
    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
    97.4
    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

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The bug requires local, low-privileged access, and the base score formally reflects only an availability impact. In practice it gives attackers a reliable path to SYSTEM, backed by public exploit code. That makes it a staple post-initial-access step after phishing or VPN compromise, and CISA flags it for known ransomware use. Exploitation likelihood is unusually high for a local-only flaw. Despite the moderate base score, rate it high to critical internally wherever you run many standard-user endpoints or shared terminal servers. For NIS2-regulated entities, any patch backlog beyond one maintenance window belongs in the risk register as a material risk.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the latest Windows cumulative security update to all Windows 10 and Windows 11 clients and to RDS/Citrix hosts. Microsoft's initial fix shipped in the November 2021 Patch Tuesday, and a public patch bypass ("InstallerFileTakeOver") followed. Target the newest cumulative update, not just the November baseline. Look up build-specific KB numbers in the Microsoft Security Update Guide.
      • Inventory patch levels: NVD references builds such as 10.0.17763.2300, 10.0.19041/19042/19043.1348 and 10.0.22000.318. Pull MECM/Intune/WSUS reports for hosts at or below these levels and tag them as critical-open. Migrate or isolate out-of-support releases (1507, 1909, 2004).
      • Patch multi-user systems first: RDS, VDI, jump hosts, kiosk and training PCs. On these, any logged-on standard user can escalate to SYSTEM.
      • Review open incidents with confirmed initial access (phishing payload, compromised VPN account). Assume SYSTEM on affected hosts, rotate local admin passwords via LAPS, and treat cached domain credentials as compromised.
      • Launch a 30-day EDR hunt using the detection rules below. Exploit code is public and has been bundled into malware campaigns.

    2. Runbook step 2

      Mitigation layers

      • Endpoint hardening: Use WDAC or AppLocker rules that block unsigned binaries from %TEMP%, %APPDATA% and C:\Users\Public. This stops the typical exploit loader before msiexec.exe is abused.
      • Windows Installer policy: The "Turn off Windows Installer" GPO (DisableMSI) reduces exposure only partially. The repair path for already-installed products stays reachable, so it does not replace the patch. Also enforce AlwaysInstallElevated = 0 via GPO.
      • IAM/least privilege: Use a tiering model to keep privileged accounts from logging on interactively to workstations. Enable Credential Guard where supported, so local SYSTEM does not translate directly into domain credential theft.
      • ASR rules (Defender for Endpoint): Set "Block credential stealing from LSASS" and "Block process creations originating from PSExec and WMI commands" to block mode. Both break common post-escalation steps.
      • Network segmentation: Move unpatchable legacy hosts into a dedicated VLAN without SMB/RDP/WinRM (445/3389/5985/5986) reach to servers and domain controllers. This contains lateral movement after a successful escalation.
      • Residual risk: For hosts that temporarily cannot be updated, document micropatching (e.g. 0patch) or a tightened EDR policy as a time-boxed compensating control with formal risk acceptance.

    3. Runbook step 3

      Detection rules

      • EDR/Sysmon EID 1: cmd.exe, powershell.exe or conhost.exe running at System integrity, spawned by elevation_service.exe (Edge/Chrome) or msiexec.exe, inside an interactive user session. KQL: DeviceProcessEvents | where InitiatingProcessFileName in~ ("elevation_service.exe","msiexec.exe") and FileName in~ ("cmd.exe","powershell.exe") and ProcessIntegrityLevel == "System"
      • Sysmon EID 11 / EID 23: Writes or deletions targeting ...\Microsoft\Edge\Application\*\elevation_service.exe or C:\Config.Msi\ by any process other than the Edge updater or TrustedInstaller. Sigma shape: TargetFilename|contains: '\elevation_service.exe' AND NOT Image|endswith: ('\MicrosoftEdgeUpdate.exe','\setup.exe').
      • Application log, source MsiInstaller (EID 1033, 1040, 11707, 11728): Repair or install operations triggered by standard users outside software-deployment windows, especially with MSI paths under %TEMP% or the user profile.
      • Security EID 4688 (command-line auditing enabled): msiexec.exe /f or /fa (repair mode) launched from a user shell or an unknown EXE. SPL: index=wineventlog EventCode=4688 New_Process_Name="*\\msiexec.exe" Process_Command_Line="*/f*" | stats count by host, Account_Name, Creator_Process_Name
      • Follow-on activity: Within minutes of a SYSTEM process appearing from a user session, correlate LSASS access (Sysmon EID 10), new services (System EID 7045) and Defender tampering (EID 5001). This chain is classic ransomware staging.

    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 Installer 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 – < 10.0.10240.19119
    • 10.0.10240.19119
    MicrosoftWindows 10 Version 1607
    • 10.0.14393.0 – < 10.0.14393.4770
    • 10.0.14393.4770
    MicrosoftWindows 10 Version 1809
    • 10.0.17763.0 – < 10.0.17763.2300
    • 10.0.17763.2300
    MicrosoftWindows 10 Version 1909
    • 10.0.0 – < 10.0.18363.1916
    • 10.0.18363.1916
    MicrosoftWindows 10 Version 2004
    • 10.0.0 – < 10.0.19041.1348
    • 10.0.19041.1348
    MicrosoftWindows 10 Version 20H2
    • 10.0.0 – < 10.0.19042.1348
    • 10.0.19042.1348
    MicrosoftWindows 10 Version 21H1
    • 10.0.0 – < 10.0.19043.1348
    • 10.0.19043.1348
    MicrosoftWindows 11 version 21H2
    • 10.0.22000.0 – < 10.0.22000.318
    • 10.0.22000.318
    MicrosoftWindows 7
    • 6.1.0 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows 7 Service Pack 1
    • 6.1.0 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows 8.1
    • 6.3.0 – < 6.3.9600.20174
    • 6.3.9600.20174
    MicrosoftWindows Server 2008 R2 Service Pack 1
    • 6.1.7601.0 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
    • 6.1.7601.0 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows Server 2008 Service Pack 2
    • 6.0.6003.0 – < 6.0.6003.21282
    • 6.0.6003.21282
    MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
    • 6.0.6003.0 – < 6.0.6003.21282
    • 6.0.6003.21282
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.23517
    • 6.2.9200.23517
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.23517
    • 6.2.9200.23517
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.20174
    • 6.3.9600.20174
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.20174
    • 6.3.9600.20174
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.4770
    • 10.0.14393.4770
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.4770
    • 10.0.14393.4770
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.2300
    • 10.0.17763.2300
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.2300
    • 10.0.17763.2300
    MicrosoftWindows Server 2022
    • 10.0.20348.0 – < 10.0.20348.350
    • 10.0.20348.350
    MicrosoftWindows Server version 2004
    • 10.0.0 – < 10.0.19041.1348
    • 10.0.19041.1348
    MicrosoftWindows Server version 20H2
    • 10.0.0 – < 10.0.19042.1348
    • 10.0.19042.1348

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_150710.0.10240.19119
    Windowsmicrosoftwindows_10_1507—
    Windowsmicrosoftwindows_10_160710.0.14393.4770
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_180910.0.17763.2300
    Windowsmicrosoftwindows_10_180910.0.18363.1916
    Windowsmicrosoftwindows_10_180910.0.19041.1348
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_10_190910.0.18363.1916
    Windowsmicrosoftwindows_10_1909—
    Windowsmicrosoftwindows_10_2004—
    Windowsmicrosoftwindows_10_20H210.0.19042.1348
    Windowsmicrosoftwindows_10_20h2—
    Windowsmicrosoftwindows_10_21H110.0.19043.1348
    Windowsmicrosoftwindows_10_21h1—
    Windowsmicrosoftwindows_11_21H210.0.22000.318
    Windowsmicrosoftwindows_11_21h2—
    Windowsmicrosoftwindows_76.1.7601.25769
    Windowsmicrosoftwindows_7—
    Windowsmicrosoftwindows_8.16.3.9600.20174
    Windowsmicrosoftwindows_8.1—
    Windowsmicrosoftwindows_rt_8.16.3.9600.20174
    Windowsmicrosoftwindows_rt_8.1—
    Windowsmicrosoftwindows_server_200410.0.19041.1348

    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. Record modifiedMicrosoft

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-41379
      Referenceremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41379
      —
      Referenceremoved
      https://www.zerodayinitiative.com/advisories/ZDI-21-1308/
      —
      Reference typeremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41379 Types: Patch, Vendor Advisory
      —
      Reference typeremoved
      https://www.zerodayinitiative.com/advisories/ZDI-21-1308/ Types: Third Party Advisory, VDB Entry
      —
      Affected versions (publisher)changed
      Windows 10 Version 1809, Windows Server 2019, Windows Server 2019 (Server Core installation) (+24)
      Windows 10 Version 1507, Windows 10 Version 1607, Windows 10 Version 1809 (+24)

      Source identifier: secure@microsoft.com

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    Badge preview for CVE-2021-41379
    <a href="https://intel.neosec.eu/en/cve/CVE-2021-41379"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-41379.svg?lang=en" alt="CVE-2021-41379 – NEOSEC Intel" height="20"></a>