CriticalCVE-2025-21335

    Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability (CVE-2025-21335)

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

    What is affected, what to do

    Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 21H2 to version 10.0.19044.5371, Microsoft Windows 10 Version 22H2 to version 10.0.19045.5371, Microsoft Windows 11 version 22H2 to version 10.0.22621.4751. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 21H2 lt 10.0.19044.0..10.0.19044.5371
    • Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.5371
    • Microsoft Windows 11 version 22H2 lt 10.0.22621.0..10.0.22621.4751
    • Microsoft Windows 11 version 22H3 lt 10.0.22631.0..10.0.22631.4751
    • Microsoft Windows 11 Version 23H2 lt 10.0.22631.0..10.0.22631.4751
    • Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.2894
    • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) lt 10.0.25398.0..10.0.25398.1369
    • Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.2894
    • Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.2894
    Fixed in
    • Microsoft Windows 10 Version 21H2 10.0.19044.5371
    • Microsoft Windows 10 Version 22H2 10.0.19045.5371
    • Microsoft Windows 11 version 22H2 10.0.22621.4751
    • Microsoft Windows 11 version 22H3 10.0.22631.4751
    • Microsoft Windows 11 Version 23H2 10.0.22631.4751
    • Microsoft Windows 11 Version 24H2 10.0.26100.2894
    • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.1369
    • Microsoft Windows Server 2025 10.0.26100.2894
    • Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.2894

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

    1.4 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 72.4

    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
    188.46 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
    1.4 %
    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
    72.4
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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 23 January 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-416

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This is a low-complexity local privilege escalation that needs only low privileges and no user interaction. It was added to KEV on Microsoft's Patch Tuesday release day as a zero-day. Attackers typically chain flaws like this after phishing or access bought from an initial-access broker, using SYSTEM rights to tamper with EDR and harvest credentials. Exploitation likelihood is currently moderate, and CISA reports no known ransomware use. Even so, organisations with large interactive Windows 11 fleets, VDI estates or Hyper-V infrastructure should roll the update out at high priority within the regular cycle (target: under 7 days), patching Hyper-V hosts and admin workstations first.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the January 2025 Patch Tuesday cumulative update and confirm the resulting build. The fix is included from these builds:

        • Windows 10 21H2: 10.0.19044.5371
        • Windows 10 22H2: 10.0.19045.5371
        • Windows 11 22H2: 10.0.22621.4751
        • Windows 11 22H3/23H2: 10.0.22631.4751
        • Windows 11 24H2 and Windows Server 2025: 10.0.26100.2894
        • Windows Server 2022, 23H2 Edition (Server Core): 10.0.25398.1369

        Look up the KB number for each build in the Microsoft Security Update Guide.

      • Inventory patch levels fleet-wide via Intune/SCCM or PowerShell: Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' | Select CurrentBuild,UBR. Treat anything below the target UBR as vulnerable.

      • Patch hosts with Hyper-V components enabled first: Hyper-V hosts, admin workstations running Hyper-V or Windows Sandbox, developer machines, and multi-user VDI/RDS hosts. Check with: Get-WindowsOptionalFeature -Online | ? FeatureName -match 'Hyper-V|DisposableClientVM'.

      • Isolate any host with a confirmed compromise (EDR network containment). Exploitation requires local code execution, so any endpoint with a recent malware or phishing alert should be treated as a possible SYSTEM-level compromise.

      • Rotate local credentials on suspect hosts: LAPS-managed local admin accounts, service accounts, and cached domain logons. SYSTEM access means LSASS is reachable.

    2. Runbook step 2

      Mitigation layers

      • Configuration change: Remove Hyper-V and Windows Sandbox wherever there is no business need:

        • Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All
        • or Containers-DisposableClientVM

        Validate dependencies on VBS, Credential Guard, WSL2 and Docker Desktop before removing. Microsoft lists no official workaround; this only reduces the attack surface.

      • Application control (endpoint hardening): Enforce WDAC or AppLocker policies that block unsigned binaries in user-writable paths (%TEMP%, %APPDATA%, Downloads, C:\Users\Public). This is where local privilege-escalation exploits are usually dropped and launched.

      • Enable Defender ASR rules, specifically:

        • "Block executable files unless they meet a prevalence, age, or trusted list criterion"
        • "Block credential stealing from LSASS"

        These limit follow-on actions after escalation.

      • IAM / least privilege: Restrict interactive and RDP logon on Hyper-V hosts and servers to Tier-0/Tier-1 admins using the GPO user rights "Allow log on locally" and "Allow log on through Remote Desktop Services". No user workloads should run on virtualisation hosts.

      • Network segmentation: Separate Hyper-V management networks (WinRM 5985/5986, RDP 3389, SMB 445) from client VLANs. SYSTEM access gained on a workstation should not translate directly into lateral movement onto virtualisation infrastructure.

    3. Runbook step 3

      Detection rules

      • EDR process ancestry: Look for a System-integrity process spawned by a Medium- or Low-integrity parent running from a user path. KQL (MDE): DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel in ("Medium","Low") and InitiatingProcessFolderPath has_any (@"\Users\", @"\Temp\")
      • Sysmon EID 1 / Security 4688: Watch for cmd.exe, powershell.exe or rundll32.exe running as NT AUTHORITY\SYSTEM with a standard-user ParentUser. Sigma shape: selection: User|endswith: 'SYSTEM' and ParentUser|not endswith: 'SYSTEM' and ParentImage|contains: '\Users\'.
      • Crash artefacts from failed exploitation: Kernel use-after-free exploits often bugcheck the host. Look for System log Event ID 1001 (BugCheck) and Event ID 41 (Kernel-Power). Investigate hosts with repeated bugchecks whose minidumps show Hyper-V integration drivers on the stack (e.g. vkrnlintvsp.sys).
      • Post-escalation activity:
        • Sysmon EID 10 with TargetImage lsass.exe and an unusual SourceImage
        • Security 4697 or System 7045 (new service)
        • Security 4720/4732 (local account created or added to Administrators) shortly after a user logon

    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 Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability

    Source: pwn.watch, Microsoft Security Update Guide, 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 21H2
    • 10.0.19044.0 – < 10.0.19044.5371
    • 10.0.19044.5371
    MicrosoftWindows 10 Version 22H2
    • 10.0.19045.0 – < 10.0.19045.5371
    • 10.0.19045.5371
    MicrosoftWindows 11 version 22H2
    • 10.0.22621.0 – < 10.0.22621.4751
    • 10.0.22621.4751
    MicrosoftWindows 11 version 22H3
    • 10.0.22631.0 – < 10.0.22631.4751
    • 10.0.22631.4751
    MicrosoftWindows 11 Version 23H2
    • 10.0.22631.0 – < 10.0.22631.4751
    • 10.0.22631.4751
    MicrosoftWindows 11 Version 24H2
    • 10.0.26100.0 – < 10.0.26100.2894
    • 10.0.26100.2894
    MicrosoftWindows Server 2022, 23H2 Edition (Server Core installation)
    • 10.0.25398.0 – < 10.0.25398.1369
    • 10.0.25398.1369
    MicrosoftWindows Server 2025
    • 10.0.26100.0 – < 10.0.26100.2894
    • 10.0.26100.2894
    MicrosoftWindows Server 2025 (Server Core installation)
    • 10.0.26100.0 – < 10.0.26100.2894
    • 10.0.26100.2894

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_21h2—
    Windowsmicrosoftwindows_10_22h2—
    Windowsmicrosoftwindows_11_22h2—
    Windowsmicrosoftwindows_11_23h2—
    Windowsmicrosoftwindows_11_24h2—
    Windowsmicrosoftwindows_server_2022_23h2—
    Windowsmicrosoftwindows_server_2025—

    Weakness classes (CWE)

    • CWE-416Use After Free

      Variant

      The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

      Entry at MITRE CWE-416

    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).

    One NVD translation into another language is hidden.

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