CriticalCVE-2026-21519

    Desktop Window Manager Elevation of Privilege Vulnerability (CVE-2026-21519)

    Published In CISA KEV since Sources: pwn.watch, CVE.org, Msrc Update Guide, EUVD

    What is affected, what to do

    Access of resource using incompatible type ('type confusion') in Desktop Window Manager allows an authorized attacker to elevate privileges locally.

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1607 to version 10.0.14393.8868, Microsoft Windows 10 Version 1809 to version 10.0.17763.8389, Microsoft Windows 10 Version 21H2 to version 10.0.19044.6937. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.8868
    • Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.8389
    • Microsoft Windows 10 Version 21H2 lt 10.0.19044.0..10.0.19044.6937
    • Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.6937
    • Microsoft Windows 11 version 22H3 lt 10.0.22631.0..10.0.22631.6649
    • Microsoft Windows 11 Version 23H2 lt 10.0.22631.0..10.0.22631.6649
    • Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.7840
    • Microsoft Windows 11 Version 25H2 lt 10.0.26200.0..10.0.26200.7840
    • Microsoft Windows 11 version 26H1 lt 10.0.28000.0..10.0.28000.1575
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.8868
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.8868
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.8389
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.8389
    • Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.4773
    • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) lt 10.0.25398.0..10.0.25398.2149
    • Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.32370
    • Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.32370
    Fixed in
    • Microsoft Windows 10 Version 1607 10.0.14393.8868
    • Microsoft Windows 10 Version 1809 10.0.17763.8389
    • Microsoft Windows 10 Version 21H2 10.0.19044.6937
    • Microsoft Windows 10 Version 22H2 10.0.19045.6937
    • Microsoft Windows 11 version 22H3 10.0.22631.6649
    • Microsoft Windows 11 Version 23H2 10.0.22631.6649
    • Microsoft Windows 11 Version 24H2 10.0.26100.7840
    • Microsoft Windows 11 Version 25H2 10.0.26200.7840
    • Microsoft Windows 11 version 26H1 10.0.28000.1575
    • Microsoft Windows Server 2016 10.0.14393.8868
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.8868
    • Microsoft Windows Server 2019 10.0.17763.8389
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.8389
    • Microsoft Windows Server 2022 10.0.20348.4773
    • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2149
    • Microsoft Windows Server 2025 10.0.26100.32370
    • Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.32370

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    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: pwn.watch, CVE.org, Msrc Update Guide, EUVD

    2.5 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 84.5

    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
    210.33 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 exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    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
    2.5 %
    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
    84.5
    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
    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-843

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This is a low-complexity local privilege escalation that needs only a standard user account and no user interaction, yet yields full control over the system's confidentiality, integrity and availability — the classic second link after phishing, a browser exploit or stolen credentials. CISA added it to KEV on the day of disclosure, which points to zero-day use; exploitation likelihood is well above average, and CISA does not currently flag ransomware campaign use. Because virtually every Windows client and many servers are affected, treat it as an expedited patch (within days), with top urgency for multi-user systems, privileged workstations and hosts with known initial access; NIS2-regulated entities should record a documented remediation deadline in their vulnerability management process.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy Microsoft's February 2026 security update (Patch Tuesday, 2026-02-10), starting with hosts where many users log on interactively: RDS/terminal servers, VDI, jump hosts, admin workstations. Target builds: Win10 1607 ≥ 10.0.14393.8868, 1809 ≥ 10.0.17763.8389, 21H2/22H2 ≥ 10.0.19044.6937 / 10.0.19045.6937, Win11 22H3/23H2 ≥ 10.0.22631.6649, 24H2 ≥ 10.0.26100.7840, 25H2 ≥ 10.0.26200.7840. Look up the KB number per build in the Microsoft Security Update Guide.
      • Check the server estate: builds 14393 and 17763 also underpin the corresponding server and LTSC editions (Server 2016/2019, Enterprise LTSC). Confirm applicability and KB in the vendor advisory and put them in the same patch ring.
      • Run a compliance query in Intune/SCCM/WSUS or Defender Vulnerability Management: flag every host below the builds above as "critical open" and record exceptions with a named owner.
      • Prioritise already-compromised users: patch or isolate hosts tied to phishing, malware or infostealer incidents from the last 30 days first — exploitation requires existing local code execution, so this bug is a second-stage step in an attack chain.
      • Rotate local admin and service account passwords (Windows LAPS) on any host with suspected compromise, as successful privilege escalation is typically followed by credential theft.

    2. Runbook step 2

      Mitigation layers

      • Configuration: Desktop Window Manager is a core OS component and cannot be disabled — there is no functional workaround. Compensating controls must limit local code execution and blast radius.
      • Application control (endpoint hardening): enforce WDAC or AppLocker policies blocking EXE/DLL/script execution from user-writable paths (%TEMP%, %APPDATA%, Downloads, C:\Users\Public); set the Defender ASR rules "Block executable files unless they meet a prevalence, age, or trusted list criterion" and "Block process creations originating from PSExec and WMI commands" to Block.
      • IAM / least privilege: restrict interactive and RDP logon on servers via GPO ("Allow log on locally" / "Allow log on through Remote Desktop Services") to required groups; temporarily restrict unpatched multi-user systems (RDS/Citrix) for non-admin users or move users to patched hosts.
      • Post-escalation containment: enable Credential Guard and LSA protection (RunAsPPL), enforce an admin tiering model (no domain admin logons on workstations), enforce Defender Tamper Protection — SYSTEM on one box should not translate directly into domain compromise.
      • Network segmentation: move unpatched exception hosts into a dedicated VLAN with tight east-west rules (no SMB/445, RDP/3389, WinRM/5985-5986 to other clients) to slow lateral movement after exploitation.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 1 / Security 4688 — child processes of dwm.exe: dwm.exe does not spawn shells in normal operation. KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "dwm.exe" and FileName in~ ("cmd.exe","powershell.exe","pwsh.exe","rundll32.exe","conhost.exe","whoami.exe").
      • DWM crashes/restarts: Application log EID 1000/1001 (Application Error / WER) with Faulting application name: dwm.exe, especially clustered or shortly before new SYSTEM processes appear — failed type-confusion attempts commonly crash DWM. SPL: index=wineventlog EventCode=1000 "dwm.exe" | stats count by host, _time.
      • Integrity-level jump in process ancestry (EDR): a process running as NT AUTHORITY\SYSTEM / System integrity whose parent chain leads back to a standard-user (Medium integrity) process. Sigma shape: ParentUser != SYSTEM AND User == SYSTEM AND ParentImage NOT IN (services.exe, svchost.exe, wininit.exe).
      • Sysmon EID 10 — access to dwm.exe: unusual processes from user paths opening TargetImage=*\dwm.exe with GrantedAccess including VM_WRITE/CREATE_THREAD (0x1F0FFF, 0x1FFFFF).
      • Follow-on activity: correlate the above with subsequent lsass.exe access (Sysmon EID 10), new local admins (Security 4732), new services (System 7045) or scheduled tasks (Security 4698) on the same host.

    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

    Access of resource using incompatible type ('type confusion') in Desktop Window Manager allows an authorized attacker to elevate privileges locally.

    Source: pwn.watch, NVD (NIST), Microsoft Security Update Guide, cvelistv5, CISA KEV Catalog, ENISA EUVD, 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 1607
    • 10.0.14393.0 – < 10.0.14393.8868
    • 10.0.14393.8868
    MicrosoftWindows 10 Version 1809
    • 10.0.17763.0 – < 10.0.17763.8389
    • 10.0.17763.8389
    MicrosoftWindows 10 Version 21H2
    • 10.0.19044.0 – < 10.0.19044.6937
    • 10.0.19044.6937
    MicrosoftWindows 10 Version 22H2
    • 10.0.19045.0 – < 10.0.19045.6937
    • 10.0.19045.6937
    MicrosoftWindows 11 version 22H3
    • 10.0.22631.0 – < 10.0.22631.6649
    • 10.0.22631.6649
    MicrosoftWindows 11 Version 23H2
    • 10.0.22631.0 – < 10.0.22631.6649
    • 10.0.22631.6649
    MicrosoftWindows 11 Version 24H2
    • 10.0.26100.0 – < 10.0.26100.7840
    • 10.0.26100.7840
    MicrosoftWindows 11 Version 25H2
    • 10.0.26200.0 – < 10.0.26200.7840
    • 10.0.26200.7840
    MicrosoftWindows 11 version 26H1
    • 10.0.28000.0 – < 10.0.28000.1575
    • 10.0.28000.1575
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.8868
    • 10.0.14393.8868
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.8868
    • 10.0.14393.8868
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.8389
    • 10.0.17763.8389
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.8389
    • 10.0.17763.8389
    MicrosoftWindows Server 2022
    • 10.0.20348.0 – < 10.0.20348.4773
    • 10.0.20348.4773
    MicrosoftWindows Server 2022, 23H2 Edition (Server Core installation)
    • 10.0.25398.0 – < 10.0.25398.2149
    • 10.0.25398.2149
    MicrosoftWindows Server 2025
    • 10.0.26100.0 – < 10.0.26100.32370
    • 10.0.26100.32370
    MicrosoftWindows Server 2025 (Server Core installation)
    • 10.0.26100.0 – < 10.0.26100.32370
    • 10.0.26100.32370

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_10_21h2—
    Windowsmicrosoftwindows_10_22h2—
    Windowsmicrosoftwindows_11_23h2—
    Windowsmicrosoftwindows_11_24h2—
    Windowsmicrosoftwindows_11_25h2—
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_2019—
    Windowsmicrosoftwindows_server_2022—
    Windowsmicrosoftwindows_server_2022_23h2—
    Windowsmicrosoftwindows_server_2025—

    Weakness classes (CWE)

    • CWE-843Access of Resource Using Incompatible Type ('Type Confusion')

      Base

      The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

      Entry at MITRE CWE-843

    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

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    <a href="https://intel.neosec.eu/en/cve/CVE-2026-21519"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-21519.svg?lang=en" alt="CVE-2026-21519 – NEOSEC Intel" height="20"></a>