Windows Cloud Files Mini Filter Driver Elevation of Privilege Vulnerability (CVE-2025-62221)
Published Last modified In CISA KEV since Sources: pwn.watch, Msrc Update Guide, CVE.org
What is affected, what to do
Use after free in Windows Cloud Files Mini Filter Driver allows an authorized attacker to elevate privileges locally.
The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1809 to version 10.0.17763.8146, Microsoft Windows 10 Version 21H2 to version 10.0.19044.6691, Microsoft Windows 10 Version 22H2 to version 10.0.19045.6691. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Microsoft Windows 10 Version 1809
lt 10.0.17763.0..10.0.17763.8146 - Microsoft Windows 10 Version 21H2
lt 10.0.19044.0..10.0.19044.6691 - Microsoft Windows 10 Version 22H2
lt 10.0.19045.0..10.0.19045.6691 - Microsoft Windows 11 version 22H3
lt 10.0.22631.0..10.0.22631.6345 - Microsoft Windows 11 Version 23H2
lt 10.0.22631.0..10.0.22631.6345 - Microsoft Windows 11 Version 24H2
lt 10.0.26100.0..10.0.26100.7462 - Microsoft Windows 11 Version 25H2
lt 10.0.26200.0..10.0.26200.7462 - Microsoft Windows Server 2019
lt 10.0.17763.0..10.0.17763.8146 - Microsoft Windows Server 2019 (Server Core installation)
lt 10.0.17763.0..10.0.17763.8146 - Microsoft Windows Server 2022
lt 10.0.20348.0..10.0.20348.4529 - Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)
lt 10.0.25398.0..10.0.25398.2025 - Microsoft Windows Server 2025
lt 10.0.26100.0..10.0.26100.7462 - Microsoft Windows Server 2025 (Server Core installation)
lt 10.0.26100.0..10.0.26100.7462
- Microsoft Windows 10 Version 1809
- Fixed in
- Microsoft Windows 10 Version 1809
10.0.17763.8146 - Microsoft Windows 10 Version 21H2
10.0.19044.6691 - Microsoft Windows 10 Version 22H2
10.0.19045.6691 - Microsoft Windows 11 version 22H3
10.0.22631.6345 - Microsoft Windows 11 Version 23H2
10.0.22631.6345 - Microsoft Windows 11 Version 24H2
10.0.26100.7462 - Microsoft Windows 11 Version 25H2
10.0.26200.7462 - Microsoft Windows Server 2019
10.0.17763.8146 - Microsoft Windows Server 2019 (Server Core installation)
10.0.17763.8146 - Microsoft Windows Server 2022
10.0.20348.4529 - Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)
10.0.25398.2025 - Microsoft Windows Server 2025
10.0.26100.7462 - Microsoft Windows Server 2025 (Server Core installation)
10.0.26100.7462
- Microsoft Windows 10 Version 1809
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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, Msrc Update Guide, CVE.org
2.5 %
EPSS score
Moderate — model estimates 1-10% exploitation likelihood.
Source: FIRST EPSS, percentile 84.7
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- 208.99 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- 84.7
- 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 10 December 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
Windows kernel privilege escalations are a staple second stage in intrusion chains. Once attackers gain initial access via phishing, stolen credentials or a webshell, they use bugs like this to go from standard user to SYSTEM, kill EDR, dump LSASS and move laterally. Exploitation needs only low-privileged local access, no user interaction and little complexity, and it yields full compromise of the host. Exploitation likelihood is well above the average CVE, and the Cloud Files minifilter has been a repeat exploitation target. CISA currently lists no known ransomware campaign use. Treat it as high priority, rising to critical on multi-user and admin systems. Accelerate it within the normal patch cycle and cover shared hosts within days.
Runbook step 1
Immediate response (0-24 h)
- Fast-track Microsoft's December 2025 security update. Target builds (Build.UBR): Windows 10 1809 / Server 2019 ≥ 10.0.17763.8146, Windows 10 21H2 ≥ 10.0.19044.6691, Windows 10 22H2 ≥ 10.0.19045.6691, Windows 11 22H3/23H2 ≥ 10.0.22631.6345, Windows 11 24H2 ≥ 10.0.26100.7462, Windows 11 25H2 ≥ 10.0.26200.7462. KB numbers are not provided here; look them up in the Microsoft Security Update Guide entry for CVE-2025-62221.
- Verify patch level fleet-wide. Query via Intune, SCCM or remote PowerShell with
(Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion').UBR. Move anything below the target UBR into a tracked remediation group. - Patch multi-user systems first. Start with RDS/terminal servers, Citrix and VDI hosts, jump hosts, admin workstations and Server 2019 boxes with interactive logons. On these hosts, one compromised standard user can reach SYSTEM and then harvest privileged credentials.
- Close out pending reboots. The fix to the
cldflt.syskernel driver only takes effect after a restart. Force or tightly schedule outstanding reboots. - Re-assess recently compromised endpoints. For hosts involved in recent phishing or malware incidents, assume local privilege escalation. Rotate local admin passwords (LAPS) and treat cached domain credentials as exposed.
Runbook step 2
Mitigation layers
- Configuration (last resort, test first): On servers and kiosks that don't need OneDrive Files On-Demand or cloud sync providers, disable the minifilter with
HKLM\SYSTEM\CurrentControlSet\Services\CldFlt\Start = 4, then reboot. This is not a vendor-endorsed workaround. It breaks OneDrive, SharePoint sync and third-party sync clients, so pilot it before wider rollout. - Endpoint hardening / application control: Use WDAC or AppLocker to block unsigned binaries running from user-writable paths (
%TEMP%,%APPDATA%,%LOCALAPPDATA%,Downloads,C:\Users\Public). Local privilege escalation exploits are almost always dropped and launched from these locations. - IAM / least privilege: Restrict interactive logon on servers via the GPO "Allow log on locally". Enforce admin tiering so privileged domain accounts never sign in to Tier 1/2 machines.
- Credential protection: Enable Credential Guard and LSA protection (
RunAsPPL), and set the ASR rule "Block credential stealing from LSASS" to block mode. The goal is that SYSTEM on one host does not translate straight into domain compromise. - EDR configuration: Keep Tamper Protection and block mode enabled. This raises the bar for typical post-SYSTEM actions such as disabling Defender or installing services.
- Configuration (last resort, test first): On servers and kiosks that don't need OneDrive Files On-Demand or cloud sync providers, disable the minifilter with
Runbook step 3
Detection rules
- Integrity-level jump in process ancestry (EDR/MDE):
DeviceProcessEvents | where InitiatingProcessIntegrityLevel in ("Low","Medium") and ProcessIntegrityLevel == "System" and InitiatingProcessFolderPath has_any (@"\AppData\", @"\Temp\", @"\Downloads\", @"\Users\Public\"). This flags SYSTEM shells such ascmd.exeorpowershell.exespawned from a parent running out of a user path. - Anomalous Cloud Files API usage (Sysmon EID 7): Alert when
cldapi.dllis loaded by processes outside%ProgramFiles%and%SystemRoot%, or by anything other than known sync clients (OneDrive.exe, Dropbox, Box). Also monitor Sysmon EID 12/13 for new keys underHKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\SyncRootManager\written by unknown processes. - Kernel crashes from failed exploit attempts: Watch the System log for clusters of Event ID 1001 (BugCheck) and 41 (Kernel-Power). Check minidumps for
cldflt.syson the stack. Use-after-free exploits frequently cause BSODs when they misfire. - Security Event ID 4688 with command-line auditing: Look for
SubjectUserSid = S-1-5-18whereParentProcessNamesits inside a user profile. Sigma shape:selection: SubjectUserSid: 'S-1-5-18' and ParentProcessName|contains: '\Users\'. - Post-exploitation correlation: On the same host, correlate an integrity jump with any of the following shortly afterwards: Event ID 7045 (new service), 4720/4732 (local user created or added to Administrators), or Sysmon EID 10 access to
lsass.exe.
- Integrity-level jump in process ancestry (EDR/MDE):
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
Use after free in Windows Cloud Files Mini Filter Driver allows an authorized attacker to elevate privileges locally.
Source: pwn.watch, Microsoft Security Update Guide, 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 versions | Fixed in | ||
|---|---|---|---|
| Microsoft | Windows 10 Version 1809 |
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| Microsoft | Windows 10 Version 21H2 |
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| Microsoft | Windows 10 Version 22H2 |
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| Microsoft | Windows 11 version 22H3 |
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| Microsoft | Windows 11 Version 23H2 |
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| Microsoft | Windows 11 Version 24H2 |
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| Microsoft | Windows 11 Version 25H2 |
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| Microsoft | Windows Server 2019 |
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| Microsoft | Windows Server 2019 (Server Core installation) |
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| Microsoft | Windows Server 2022 |
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| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) |
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| Microsoft | Windows Server 2025 |
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| Microsoft | Windows Server 2025 (Server Core installation) |
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Vendors and products
- Microsoft Microsoft Windows 10 1809
- Microsoft Microsoft Windows 10 21H2
- Microsoft Microsoft Windows 10 22h2
- Microsoft Windows 10 Version 1809
- Microsoft Windows 10 Version 21h2
- Microsoft Windows 10 Version 22h2
- Microsoft Microsoft Windows 11 23H2
- Microsoft Microsoft Windows 11 24H2
- Microsoft Microsoft Windows 11 25H2
- Microsoft Windows 11 Version 22h3
- Microsoft Windows 11 Version 23h2
- Microsoft Windows 11 Version 24h2
Affected operating systems
| Windows | microsoft | windows_10_1809 | — |
| Windows | microsoft | windows_10_21h2 | — |
| Windows | microsoft | windows_10_22h2 | — |
| Windows | microsoft | windows_11_23h2 | — |
| Windows | microsoft | windows_11_24h2 | — |
| Windows | microsoft | windows_11_25h2 | — |
| Windows | microsoft | windows_server_2019 | — |
| Windows | microsoft | windows_server_2022 | — |
| Windows | microsoft | windows_server_2022_23h2 | — |
| Windows | microsoft | windows_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.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- Microsoft Security Update GuideWindows Cloud Files Mini Filter Driver Elevation of Privilege VulnerabilityVendor advisory, Patch
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-62221government-resource
- pwn.watchpwn.watch: Microsoft Windows: Windows Use After Free Vulnerabilitypwn-watch
- Microsoft Security Update GuideMicrosoft advisory: Microsoft Windowspwn-watch
- NVD (NIST)NVD: CVE-2025-62221pwn-watch
- cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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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<a href="https://intel.neosec.eu/en/cve/CVE-2025-62221"><img src="https://intel.neosec.eu/badge/cve/CVE-2025-62221.svg?lang=en" alt="CVE-2025-62221 – NEOSEC Intel" height="20"></a>