CriticalCVE-2026-21510

Windows Shell Security Feature Bypass Vulnerability (CVE-2026-21510)

Published 10.02.2026In CISA KEV since 10.02.2026Sources: CVE.org, pwn.watch, Msrc Update Guide, EUVD

What is affected, what to do

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

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 2012 lt 6.2.9200.0..6.2.9200.25923
Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.25923
Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.23022
Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.23022
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 2012 6.2.9200.25923
Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.25923
Microsoft Windows Server 2012 R2 6.3.9600.23022
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.23022
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

8.8

Priority

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

Source: NVD, CVSS v3

8.8

CVSS v3

Severity High on the scale from 0 to 10.

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

61.2 %

EPSS score

High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

Source: FIRST EPSS, percentile 99.16

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: 236.92 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: 8.8 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: 8.8
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: 61.2 %; High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
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: 99.16; 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: 10.02.2026
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: 10.02.2026
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-693

Response and mitigation

Why act now?

Prioritisation rationale

This CVE is on KEV because it circumvents a core Windows protection surface (very likely MOTW/SmartScreen in the Shell context) and is being chained into phishing and drive-by delivery as an initial-access building block that then stages loaders, infostealers and ransomware precursors. The chain requires user interaction (opening a crafted file) but is reachable across the network and yields full code execution in the user context, which places it among the vulnerabilities most likely to be exploited in the near term. Prioritise all endpoints with email and browsing privileges ahead of back-end servers; in NIS2-regulated environments the rollout belongs in the regular monthly change window, with an emergency change inside 72 hours for exposed VDI/RDS farms.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the Microsoft February 2026 Patch Tuesday update across all Windows 10 and 11 estates. Target builds: Win10 1607 → 10.0.14393.8868, Win10 1809 → 10.0.17763.8389, Win10 21H2/22H2 → 10.0.19044.6937 / 10.0.19045.6937, Win11 22H3/23H2 → 10.0.22631.6649, Win11 24H2 → 10.0.26100.7840, Win11 25H2 → 10.0.26200.7840.
- Rollout order via WSUS/Intune/SCCM rings: internet-facing user workstations, mail- and browser-heavy endpoints (Office clients, VDI, jump hosts) first; interactive servers (RDS, Citrix) next.
- Validate Mark-of-the-Web plumbing: the GPO "Do not preserve zone information in file attachments" must remain disabled so Shell-level protections (SmartScreen, Protected View) can trigger. Review Attachment Manager zone mappings for Internet/Restricted Sites.
- Tighten the perimeter: have the mail gateway block container formats (.iso, .img, .vhd, .vhdx, .lnk, .url, .scf, .library-ms, .search-ms) and the same payloads inside .zip/.7z. These are the typical MOTW/Shell bypass carriers.
- If patching has to wait: place affected hosts in an isolated VLAN, deny outbound SMB (TCP 445) and WebDAV to non-allowlisted destinations, and restrict browser downloads to approved sources.
02
Runbook step 2
Mitigation layers
- Network segmentation: egress-deny TCP 445 and restrict WebDAV (HTTP OPTIONS/PROPFIND) to an allowlist on the proxy. Shell-bypass chains frequently stage payloads via UNC or WebDAV.
- Endpoint hardening: disable the WebClient service on workstations where WebDAV is not required (sc config WebClient start= disabled). This neutralises a large class of MOTW/Shell bypasses.
- Enable Microsoft Defender ASR rules: BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550 (block executables from email/webmail), D4F940AB-401B-4EFC-AADC-AD5F3C50688A (block Office child processes), D3E037E1-3EB8-44C8-A917-57927947596D (block JS/VBS launched from downloads).
- AppLocker/WDAC: restrict execution from %LOCALAPPDATA%\Temp, %APPDATA%, Downloads folders and mounted ISO/VHD volumes to signed binaries. Block .lnk, .scf, .url and MSI launched from user-writable paths.
- Enforce SmartScreen and Protected View via GPO; configure Attachment Manager so high-risk file types always receive MOTW.
- Mail policy: strip embedded external resources from HTML mail, enforce URL rewriting and attachment detonation.
03
Runbook step 3
Detection rules
- Sysmon EID 15 (FileCreateStreamHash): absence of a Zone.Identifier stream on files written by browser or mail-client processes indicates MOTW stripping. Sigma shape: EventID: 15 AND TargetFilename|endswith: ('.exe','.dll','.lnk','.hta','.js','.vbs') AND NOT Contents|contains: 'ZoneId'.
- Sysmon EID 1 with parent explorer.exe spawning mshta.exe, wscript.exe, cscript.exe, rundll32.exe or regsvr32.exe from user download paths. KQL (Defender): DeviceProcessEvents | where InitiatingProcessFileName == "explorer.exe" and FileName in ("mshta.exe","wscript.exe","rundll32.exe") and ProcessCommandLine has_any ("\\Downloads\\","\\Temp\\","\\AppData\\").
- Windows Event ID 4688 or Sysmon EID 1 showing .lnk execution whose target is a UNC path (\\<host>\...) or an http(s):// URL — classic Shell handler abuse.
- Zeek/Suricata: WebDAV verbs (PROPFIND, OPTIONS) from endpoints to non-corporate hosts; TCP 445 traffic from workstations to public IPs.
- EDR telemetry: ISO/VHD/VHDX mount events driven by explorer.exe or vmms.exe on standard workstations (unusual outside admin hosts). Microsoft-Windows-VHDMP-Operational log Event IDs 1006/1016.

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

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

Source: NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), pwn.watch, Microsoft Security Update Guide, cvelistv5, ENISA EUVD

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 1607	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows 10 Version 21H2	`10.0.19044.0 – < 10.0.19044.6937`	`10.0.19044.6937`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.6937`	`10.0.19045.6937`
Microsoft	Windows 11 version 22H3	`10.0.22631.0 – < 10.0.22631.6649`	`10.0.22631.6649`
Microsoft	Windows 11 Version 23H2	`10.0.22631.0 – < 10.0.22631.6649`	`10.0.22631.6649`
Microsoft	Windows 11 Version 24H2	`10.0.26100.0 – < 10.0.26100.7840`	`10.0.26100.7840`
Microsoft	Windows 11 Version 25H2	`10.0.26200.0 – < 10.0.26200.7840`	`10.0.26200.7840`
Microsoft	Windows 11 version 26H1	`10.0.28000.0 – < 10.0.28000.1575`	`10.0.28000.1575`
Microsoft	Windows Server 2012	`6.2.9200.0 – < 6.2.9200.25923`	`6.2.9200.25923`
Microsoft	Windows Server 2012 (Server Core installation)	`6.2.9200.0 – < 6.2.9200.25923`	`6.2.9200.25923`
Microsoft	Windows Server 2012 R2	`6.3.9600.0 – < 6.3.9600.23022`	`6.3.9600.23022`
Microsoft	Windows Server 2012 R2 (Server Core installation)	`6.3.9600.0 – < 6.3.9600.23022`	`6.3.9600.23022`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.4773`	`10.0.20348.4773`
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	`10.0.25398.0 – < 10.0.25398.2149`	`10.0.25398.2149`
Microsoft	Windows Server 2025	`10.0.26100.0 – < 10.0.26100.32370`	`10.0.26100.32370`
Microsoft	Windows 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

Windows	microsoft	windows_10_1607	—
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_2012	`r2`
Windows	microsoft	windows_server_2012	—
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-693Protection Mechanism Failure
Pillar
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
Entry at MITRE CWE-693

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	10.02.2026

References & sources

Microsoft Security Update GuideWindows Shell Security Feature Bypass Vulnerabilityeuvd, Vendor advisory, Patch, Vendor advisory, pwn-watch
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21510government-resource, US government resource
pwn.watchpwn.watch: Microsoft Windows: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerabilitypwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-21513pwn-watch
NVD (NIST)NVD: CVE-2026-21513pwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-21525pwn-watch
NVD (NIST)NVD: CVE-2026-21525pwn-watch
NVD (NIST)NVD: CVE-2026-21510pwn-watch

Linked advisories

October Patch Tuesday roundup: Over 1,400 Microsoft holes to be plugged, including three zero daysCSO Online14.10.2026

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-21510"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-21510.svg?lang=en" alt="CVE-2026-21510 – 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

Linked advisories