CriticalCVE-2025-21391

Windows Storage Elevation of Privilege Vulnerability (CVE-2025-21391)

Published 11.02.2025Last modified 24.09.2026In CISA KEV since 11.02.2025Sources: pwn.watch, Msrc Update Guide, CVE.org

What is affected, what to do

Windows Storage Elevation of Privilege Vulnerability

The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1507 to version 10.0.10240.20915, Microsoft Windows 10 Version 1607 to version 10.0.14393.7785, Microsoft Windows 10 Version 1809 to version 10.0.17763.6893. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 10 Version 1507 lt 10.0.10240.0..10.0.10240.20915
Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.7785
Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.6893
Microsoft Windows 10 Version 21H2 lt 10.0.19044.0..10.0.19044.5487
Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.5487
Microsoft Windows 11 version 22H2 lt 10.0.22621.0..10.0.22621.4890
Microsoft Windows 11 version 22H3 lt 10.0.22631.0..10.0.22631.4890
Microsoft Windows 11 Version 23H2 lt 10.0.22631.0..10.0.22631.4890
Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.3194
Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.7785
Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.7785
Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.6893
Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.6893
Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.3207
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) lt 10.0.25398.0..10.0.25398.1425
Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.3194
Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.3194
Fixed in: Microsoft Windows 10 Version 1507 10.0.10240.20915
Microsoft Windows 10 Version 1607 10.0.14393.7785
Microsoft Windows 10 Version 1809 10.0.17763.6893
Microsoft Windows 10 Version 21H2 10.0.19044.5487
Microsoft Windows 10 Version 22H2 10.0.19045.5487
Microsoft Windows 11 version 22H2 10.0.22621.4890
Microsoft Windows 11 version 22H3 10.0.22631.4890
Microsoft Windows 11 Version 23H2 10.0.22631.4890
Microsoft Windows 11 Version 24H2 10.0.26100.3194
Microsoft Windows Server 2016 10.0.14393.7785
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.7785
Microsoft Windows Server 2019 10.0.17763.6893
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.6893
Microsoft Windows Server 2022 10.0.20348.3207
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.1425
Microsoft Windows Server 2025 10.0.26100.3194
Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.3194

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Metrics

7.1

Priority

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

Source: NVD, CVSS v3

7.1

CVSS v3

Severity High on the scale from 0 to 10.

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

2.3 %

EPSS score

Moderate — model estimates 1-10% exploitation likelihood.

Source: FIRST EPSS, percentile 83.0

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: 198.52 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: 7.1 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: 7.1
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: 2.3 %; 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: 83.0; 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: 11.02.2025
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: 11.02.2025
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-59

Response and mitigation

Why act now?

Prioritisation rationale

This CVE is on KEV because, despite requiring local authenticated access, it delivers a reliable primitive to escalate from a low-privileged user to SYSTEM — exactly the second-stage capability attackers chain after phishing, browser exploitation or infostealer infections. CISA has not flagged ransomware use, but link-following flaws against privileged services are standard tooling for both commodity loaders and targeted operations. Treat it as high priority on any multi-user system or endpoint where untrusted code can run in user context; dedicated single-user admin workstations with a strict allowlist carry lower residual risk, yet the patch remains mandatory within the February Patch Tuesday cycle.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the February 2025 Patch Tuesday update across every affected Windows build. Target builds per MSRC: Windows 10 1507 → 10.0.10240.20915, 1607 → 10.0.14393.7785, 1809 → 10.0.17763.6893, 21H2/22H2 → 10.0.19044.5487 / 10.0.19045.5487, Windows 11 22H2/23H2 → 10.0.22621.4890 / 10.0.22631.4890.
- Patch multi-user systems first: Terminal/RDS servers, jump hosts, VDI pools, shared developer workstations. The required low-privileged authenticated foothold is most realistic there.
- Temporarily restrict interactive and RDP logons on server-class systems to administrative accounts (GPO "Allow log on locally" and "Allow log on through Remote Desktop Services") until the patch has landed.
- Review AppLocker/WDAC policy and confirm unprivileged users cannot launch arbitrary binaries from %TEMP%, %APPDATA% or Downloads — local code execution in user context is a prerequisite for exploitation.
- Identify end-of-life SKUs (1507/1607/1809 outside LTSC support). If no update ships through standard channels, raise a change ticket for isolation or replacement.
02
Runbook step 2
Mitigation layers
- Endpoint hardening: enforce least privilege rigorously — remove local admin rights, deploy LAPS for local admin accounts, set UAC to "Always Notify". Won't block the EoP itself, but shrinks the attack surface before it.
- Enable EDR tamper protection and Credential Guard so that a successful jump to SYSTEM does not immediately translate into LSASS dumping or EDR disablement.
- Filesystem hardening: audit symlink evaluation with fsutil behavior query SymlinkEvaluation and disable remote-to-local / remote-to-remote symlinks (fsutil behavior set SymlinkEvaluation R2L:0 R2R:0). Narrows the broader link-following attack class.
- Network segmentation: block workstation-to-workstation SMB (TCP 445) at the host firewall so a compromised user account cannot pivot to escalate on peer endpoints.
- Track patch compliance in SCCM/Intune/WSUS with a hard deadline; automatically move non-compliant assets into a quarantine VLAN.
- For unpatched legacy systems: allow interactive access only via a Privileged Access Workstation (PAW), strip non-essential services, raise monitoring sensitivity.
03
Runbook step 3
Detection rules
- Sysmon EID 11 (FileCreate) and EID 2 on junction/symlink creation by non-admin processes under writable paths such as C:\Windows\Temp, C:\ProgramData, %LOCALAPPDATA%. Sigma shape: user-shell Image|endswith combined with TargetFilename|contains of privileged paths.
- Sysmon EID 1 (ProcessCreate) on cmd.exe /c mklink /J, New-Item -ItemType Junction or CreateSymbolicLink API usage from non-admin parents. KQL skeleton: DeviceProcessEvents | where ProcessCommandLine has_any ("mklink /J","mklink /D") and InitiatingProcessAccountName !in (admin-list).
- Windows Security EID 4663 (Object Access) with ObjectName pointing at SYSTEM-protected paths (e.g. C:\Windows\System32\config, C:\Windows\ServiceProfiles), SubjectUserSid a standard user, and AccessMask 0x10000 (DELETE).
- EDR process chains in which a SYSTEM parent suddenly launches shell payloads owned by a user SID — a generic post-EoP indicator useful beyond this specific CVE.
- Crashes of the Windows Storage Service / svchost.exe hosting StorageService (System EID 7031, 7034), especially right after file operations by a standard user — likely a failed exploit attempt.

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 Storage 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 versions	Fixed in
Microsoft	Windows 10 Version 1507	`10.0.10240.0 – < 10.0.10240.20915`	`10.0.10240.20915`
Microsoft	Windows 10 Version 1607	`10.0.14393.0 – < 10.0.14393.7785`	`10.0.14393.7785`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.6893`	`10.0.17763.6893`
Microsoft	Windows 10 Version 21H2	`10.0.19044.0 – < 10.0.19044.5487`	`10.0.19044.5487`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.5487`	`10.0.19045.5487`
Microsoft	Windows 11 version 22H2	`10.0.22621.0 – < 10.0.22621.4890`	`10.0.22621.4890`
Microsoft	Windows 11 version 22H3	`10.0.22631.0 – < 10.0.22631.4890`	`10.0.22631.4890`
Microsoft	Windows 11 Version 23H2	`10.0.22631.0 – < 10.0.22631.4890`	`10.0.22631.4890`
Microsoft	Windows 11 Version 24H2	`10.0.26100.0 – < 10.0.26100.3194`	`10.0.26100.3194`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.7785`	`10.0.14393.7785`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.7785`	`10.0.14393.7785`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.6893`	`10.0.17763.6893`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.6893`	`10.0.17763.6893`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.3207`	`10.0.20348.3207`
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	`10.0.25398.0 – < 10.0.25398.1425`	`10.0.25398.1425`
Microsoft	Windows Server 2025	`10.0.26100.0 – < 10.0.26100.3194`	`10.0.26100.3194`
Microsoft	Windows Server 2025 (Server Core installation)	`10.0.26100.0 – < 10.0.26100.3194`	`10.0.26100.3194`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1507	—
Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_21h2	—
Windows	microsoft	windows_10_22h2	—
Windows	microsoft	windows_11_22h2	—
Windows	microsoft	windows_11_23h2	—
Windows	microsoft	windows_11_24h2	—
Windows	microsoft	windows_server_2016	—
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-59Improper Link Resolution Before File Access ('Link Following')
Base
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
Entry at MITRE CWE-59

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 Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	11.02.2025

References & sources

Microsoft Security Update GuideWindows Storage Elevation of Privilege VulnerabilityVendor advisory, Patch, pwn-watch
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21391government-resource
pwn.watchpwn.watch: Microsoft Windows: 2 exploited vulnerabilities (CVE-2025-21391, CVE-2025-21418)pwn-watch
Microsoft Security Update GuideMicrosoft advisory: Microsoft Windowspwn-watch
NVD (NIST)NVD: CVE-2025-21391pwn-watch
NVD (NIST)NVD: CVE-2025-21418pwn-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-2025-21391"><img src="https://intel.neosec.eu/badge/cve/CVE-2025-21391.svg?lang=en" alt="CVE-2025-21391 – NEOSEC Intel" height="20"></a>

What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources

Changes to this CVE