CriticalCVE-2022-24521

    Windows Common Log File System Driver Elevation of Privilege Vulnerability (CVE-2022-24521)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Windows Common Log File System Driver 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 1809 to version 10.0.17763.2803, Microsoft Windows Server 2019 to version 10.0.17763.2803, Microsoft Windows Server 2019 (Server Core installation) to version 10.0.17763.2803. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.2803
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.2803
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.2803
    • Microsoft Windows 10 Version 1909 lt 10.0.0..10.0.18363.2212
    • Microsoft Windows 10 Version 21H1 lt 10.0.0..10.0.19043.1645
    • Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.643
    • Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.1645
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1645
    • Microsoft Windows 11 version 21H2 lt 10.0.0..10.0.22000.613
    • Microsoft Windows 10 Version 21H2 lt 10.0.19043.0..10.0.19044.1645
    • Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.19265
    • Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.5066
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.5066
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.5066
    • Microsoft Windows 7 lt 6.1.0..6.1.7601.25924
    • Microsoft Windows 7 Service Pack 1 lt 6.1.0..6.1.7601.25924
    • Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20337
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.21446
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.21446
    • Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.7601.0..6.1.7601.25924
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.25924
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.23679
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.23679
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20337
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20337
    Fixed in
    • Microsoft Windows 10 Version 1809 10.0.17763.2803
    • Microsoft Windows Server 2019 10.0.17763.2803
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2803
    • Microsoft Windows 10 Version 1909 10.0.18363.2212
    • Microsoft Windows 10 Version 21H1 10.0.19043.1645
    • Microsoft Windows Server 2022 10.0.20348.643
    • Microsoft Windows 10 Version 20H2 10.0.19042.1645
    • Microsoft Windows Server version 20H2 10.0.19042.1645
    • Microsoft Windows 11 version 21H2 10.0.22000.613
    • Microsoft Windows 10 Version 21H2 10.0.19044.1645
    • Microsoft Windows 10 Version 1507 10.0.10240.19265
    • Microsoft Windows 10 Version 1607 10.0.14393.5066
    • Microsoft Windows Server 2016 10.0.14393.5066
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.5066
    • Microsoft Windows 7 6.1.7601.25924
    • Microsoft Windows 7 Service Pack 1 6.1.7601.25924
    • Microsoft Windows 8.1 6.3.9600.20337
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21446
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21446
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25924
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25924
    • Microsoft Windows Server 2012 6.2.9200.23679
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23679
    • Microsoft Windows Server 2012 R2 6.3.9600.20337
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20337

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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: CVE.org

    7.1 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 94.2

    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
    235.74 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
    7.1 %
    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
    94.2
    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

    CVE-2022-24521 is a low-complexity local privilege escalation: any foothold in a standard user context becomes full SYSTEM control with no user interaction, giving complete impact on confidentiality, integrity and availability. It was exploited as a zero-day, and CISA explicitly flags known ransomware campaign use. Attackers chain it after phishing or stolen credentials to kill EDR, dump credentials and stage encryption. Its exploitation likelihood ranks well above most published CVEs, so organisations with multi-user hosts, VDI or a large client estate should treat it as top patch priority. Once the April 2022 baseline is confirmed fleet-wide, the effort shifts to hunting down legacy stragglers and retrospective compromise assessment.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the April 2022 cumulative security update (or any later one). The listed builds are the fixed versions. Anything below them is vulnerable: Windows 10 1507 < 10.0.10240.19265, 1607 < 10.0.14393.5066, 1809 < 10.0.17763.2803, 1909 < 10.0.18363.2212, 20H2 < 10.0.19042.1645, 21H1 < 10.0.19043.1645, 21H2 < 10.0.19044.1645, and Windows 11 21H2 < 10.0.22000.613. Per-version KB numbers are in the MSRC advisory for CVE-2022-24521. Check server editions, especially RDS and Citrix hosts, against the same advisory.
      • Inventory vulnerable endpoints by querying the OS build in MECM, Intune or Defender TVM. Patch multi-user systems first (terminal servers, VDI, jump hosts): a single compromised user account on them is enough to reach SYSTEM.
      • Handle systems you cannot patch. Legacy assets, OT HMIs and out-of-support Windows 10 1507/1909 should be pulled off the production network, or interactive and local logons on them should be tightly restricted.
      • Run a retrospective hunt for the CLFS indicators below, going back to April 2022, on every host that was patched late. Treat any hit as a full compromise: isolate the asset and rotate all credentials cached on it, especially domain and service accounts.
      • Close the initial-access paths in parallel. Exploitation requires code execution as a standard user first, so harden the usual precursors: phishing attachments, macros and exposed RDP.

    2. Runbook step 2

      Mitigation layers

      • Endpoint hardening: There is no vendor workaround. The CLFS driver (clfs.sys) cannot be disabled without breaking the OS. Enforce EDR protections such as Defender Tamper Protection and ASR rules, including "Block executable files unless they meet a prevalence, age, or trusted list criterion".
      • Application control: Use WDAC or AppLocker to block unsigned binaries from user-writable paths (%TEMP%, %APPDATA%, C:\Users\Public, Downloads). Exploits for this flaw are usually standalone EXEs or DLLs dropped into these locations.
      • IAM / least privilege: Strip local admin rights, deploy LAPS, and enable Credential Guard and LSA Protection (RunAsPPL). This limits credential theft after a SYSTEM escalation and slows lateral movement.
      • Network segmentation: Put unpatched hosts in a quarantine VLAN. Block SMB (445/tcp), RDP (3389/tcp) and WinRM (5985/5986/tcp) from that VLAN towards servers and domain controllers, and force egress through an allowlisting proxy.
      • Admin tiering: Never let Tier 0/1 accounts log on to Tier 2 workstations. Otherwise a locally escalated attacker can harvest those privileged credentials.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 11 / EDR file events: Creation of .blf files (CLFS base log files) by non-system processes in user paths. KQL: DeviceFileEvents | where FileName endswith ".blf" and FolderPath has_any ("\\Users\\","\\Temp\\","\\ProgramData\\") and InitiatingProcessFileName !in~ ("svchost.exe","System").
      • Integrity-level jump in process ancestry (Sysmon EID 1 / Security 4688): A process running at IntegrityLevel=System whose parent is a medium-integrity user binary rather than services.exe, winlogon.exe or wininit.exe. The classic pattern is cmd.exe/powershell.exe running as SYSTEM under an unknown binary in %TEMP%. Sigma shape: IntegrityLevel: System combined with ParentImage|contains: '\Users\'.
      • Crash artefacts from failed exploit attempts: Event ID 1001 (BugCheck) or Event ID 41 (Kernel-Power) close in time to .blf creation. Triage any minidump with clfs.sys on the stack.
      • Post-escalation activity: Access to lsass.exe (Sysmon EID 10, GrantedAccess 0x1010/0x1410), Event 4672 for unusual accounts, new service installs (System 7045) and vssadmin delete shadows. This combination indicates ransomware staging.
      • EDR alert correlation: Join CLFS or privilege-escalation exploit alerts with each host's patch level. A hit on an unpatched build gets top priority.

    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 Common Log File System Driver Elevation of Privilege Vulnerability

    Source: cvelistv5, NVD (NIST), 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 1507
    • 10.0.10240.0 – < 10.0.10240.19265
    • 10.0.10240.19265
    MicrosoftWindows 10 Version 1607
    • 10.0.14393.0 – < 10.0.14393.5066
    • 10.0.14393.5066
    MicrosoftWindows 10 Version 1809
    • 10.0.17763.0 – < 10.0.17763.2803
    • 10.0.17763.2803
    MicrosoftWindows 10 Version 1909
    • 10.0.0 – < 10.0.18363.2212
    • 10.0.18363.2212
    MicrosoftWindows 10 Version 20H2
    • 10.0.0 – < 10.0.19042.1645
    • 10.0.19042.1645
    MicrosoftWindows 10 Version 21H1
    • 10.0.0 – < 10.0.19043.1645
    • 10.0.19043.1645
    MicrosoftWindows 10 Version 21H2
    • 10.0.19043.0 – < 10.0.19044.1645
    • 10.0.19044.1645
    MicrosoftWindows 11 version 21H2
    • 10.0.0 – < 10.0.22000.613
    • 10.0.22000.613
    MicrosoftWindows 7
    • 6.1.0 – < 6.1.7601.25924
    • 6.1.7601.25924
    MicrosoftWindows 7 Service Pack 1
    • 6.1.0 – < 6.1.7601.25924
    • 6.1.7601.25924
    MicrosoftWindows 8.1
    • 6.3.0 – < 6.3.9600.20337
    • 6.3.9600.20337
    MicrosoftWindows Server 2008 R2 Service Pack 1
    • 6.1.7601.0 – < 6.1.7601.25924
    • 6.1.7601.25924
    MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
    • 6.1.7601.0 – < 6.1.7601.25924
    • 6.1.7601.25924
    MicrosoftWindows Server 2008 Service Pack 2
    • 6.0.6003.0 – < 6.0.6003.21446
    • 6.0.6003.21446
    MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
    • 6.0.6003.0 – < 6.0.6003.21446
    • 6.0.6003.21446
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.23679
    • 6.2.9200.23679
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.23679
    • 6.2.9200.23679
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.20337
    • 6.3.9600.20337
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.20337
    • 6.3.9600.20337
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.5066
    • 10.0.14393.5066
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.5066
    • 10.0.14393.5066
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.2803
    • 10.0.17763.2803
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.2803
    • 10.0.17763.2803
    MicrosoftWindows Server 2022
    • 10.0.20348.0 – < 10.0.20348.643
    • 10.0.20348.643
    MicrosoftWindows Server version 20H2
    • 10.0.0 – < 10.0.19042.1645
    • 10.0.19042.1645

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_1507—
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_10_1909—
    Windowsmicrosoftwindows_10_20h2—
    Windowsmicrosoftwindows_10_21h1—
    Windowsmicrosoftwindows_10_21h2—
    Windowsmicrosoftwindows_11_21h2—
    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—
    Windowsmicrosoftwindows_server_2022—
    Windowsmicrosoftwindows_server_20h2—

    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

    • Microsoft Security Update GuideWindows Common Log File System Driver Elevation of Privilege VulnerabilityVendor advisory, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2022-24521government-resource, US government resource
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    <a href="https://intel.neosec.eu/en/cve/CVE-2022-24521"><img src="https://intel.neosec.eu/badge/cve/CVE-2022-24521.svg?lang=en" alt="CVE-2022-24521 – NEOSEC Intel" height="20"></a>