CriticalCVE-2026-21533

Windows Remote Desktop Services Elevation of Privilege Vulnerability (CVE-2026-21533)

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

What is affected, what to do

Improper privilege management in Windows Remote Desktop allows an authorized attacker to elevate privileges locally.

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

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, EUVD, CVE.org, Msrc Update Guide

4.2 %

EPSS score

Moderate — model estimates 1-10% exploitation likelihood.

Source: FIRST EPSS, percentile 90.9

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: 219.31 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: 4.2 %; 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: 90.9; 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-269

Response and mitigation

Why act now?

Prioritisation rationale

This flaw requires an existing authenticated local foothold, so it is not an initial-access vector. It is, however, a dependable step for turning a phished user, stolen VPN/RDP credentials or a compromised service account into SYSTEM on the box. Functional exploit code exists, an official fix is available, and exploitation likelihood sits well above the typical CVE. CISA does not currently flag ransomware use. Shared RDS/VDI estates, jump hosts and any organisation exposing RDP externally should patch within an emergency window (≤ 72 h). Single-user clients without inbound RDP can ride the regular patch cycle, provided it completes in February.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the February 2026 Windows cumulative security update. Look up the per-release KB number in the Microsoft Security Update Guide entry for CVE-2026-21533. Fixed builds are 10.0.14393.8868 (1607), 10.0.17763.8389 (1809), 10.0.19044.6937 / 10.0.19045.6937 (21H2/22H2), 10.0.22631.6649 (22H3/23H2) and 10.0.26100.7840 / 10.0.26200.7840 (24H2/25H2).
- Patch high-user-density hosts first: RDS session hosts, terminal servers, jump boxes and VDI pools. Then patch admin workstations, and finally standard clients. Verify Server editions on the 14393/17763 build lines (Server 2016/2019) against the vendor advisory.
- Inventory build levels fleet-wide via Intune, MECM or Defender Vulnerability Management. Alternatively use PowerShell: (Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion').CurrentBuild,UBR. Track non-compliant hosts as time-boxed exceptions.
- On unpatched multi-user hosts, restrict "Allow log on through Remote Desktop Services" to the groups that genuinely need it. Remove stale or unnecessary accounts from "Remote Desktop Users".
- On clients that do not need inbound RDP, disable TermService or set fDenyTSConnections=1 via GPO. Confirm in the advisory whether exploitation requires an active RDP session.
- If compromise is suspected, isolate the host. Then rotate local admin passwords (LAPS) and the credentials of every account that logged on interactively since the last patch window.
02
Runbook step 2
Mitigation layers
- Network segmentation: Allow TCP/UDP 3389 only from dedicated admin/PAW subnets or through RD Gateway (TCP 443). Block client-to-client RDP with host firewall GPOs.
- IAM / least privilege: Enforce the tiering model so that Tier-0 accounts never log on to RDS hosts shared with standard users. Use Protected Users and Restricted Admin or Remote Credential Guard so that a SYSTEM-level attacker finds no reusable credentials in LSASS.
- Endpoint hardening: Enable these ASR rules: "Block credential stealing from LSASS" and "Block process creations originating from PSExec and WMI commands". Also enable LSA Protection (RunAsPPL) and Credential Guard to blunt post-escalation activity.
- Application control: Run WDAC or AppLocker in enforce mode on session hosts. Block execution from user-writable paths (%TEMP%, %APPDATA%, C:\Users\Public), where local exploits are typically staged.
- Configuration: Enforce NLA and set timeouts for disconnected sessions. Disable drive and clipboard redirection where it is not needed, to make it harder to bring exploit binaries onto the host.
03
Runbook step 3
Detection rules
- Sysmon EID 1 / Security 4688: A process running as NT AUTHORITY\SYSTEM or with System integrity whose parent ran at Medium integrity in a user session (SessionId > 0). KQL: DeviceProcessEvents | where ProcessIntegrityLevel=="System" and InitiatingProcessIntegrityLevel=="Medium"
- EDR process ancestry: Unusual children of svchost.exe -k termsvcs, rdpclip.exe, rdpinit.exe or TSTheme.exe, especially cmd.exe, powershell.exe, rundll32.exe or unsigned binaries. Sigma shape: ParentImage|endswith: ['\rdpclip.exe','\rdpinit.exe'] AND Image|endswith: ['\cmd.exe','\powershell.exe']
- Logon-to-privilege correlation: Security 4624 with LogonType 10 (RemoteInteractive) by a non-admin. Within 30 minutes on the same host, look for 4672 (special privileges), 7045/4697 (new service), 4720/4732 (account created or added to Administrators) or a new scheduled task (4698).
- Follow-on activity: LSASS access (Sysmon EID 10, TargetImage ending in \lsass.exe, GrantedAccess 0x1010/0x1410) and file writes to C:\Windows\System32 by processes launched from user-profile paths.
- Telemetry tampering: Treat event 1102 (Security log cleared) and event 104 (System log cleared) on RDS hosts as high-severity.

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

Improper privilege management in Windows Remote Desktop allows an authorized attacker to elevate privileges locally.

Source: pwn.watch, ENISA EUVD, NVD (NIST), Microsoft Security Update Guide, 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 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-269Improper Privilege Management
Class
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.
Entry at MITRE CWE-269

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 Remote Desktop Services Elevation of Privilege Vulnerabilityeuvd, Vendor advisory, Patch, Vendor advisory
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21533government-resource, US government resource
vicarius.iovsociety/posts/cve-2026-21533-detection-script-privilege-escala…Third-party advisory
vicarius.iovsociety/posts/cve-2026-21533-mitigation-script-privilege-escal…Mitigation, Third-party advisory
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
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-21510pwn-watch
NVD (NIST)NVD: CVE-2026-21510pwn-watch

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-21533"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-21533.svg?lang=en" alt="CVE-2026-21533 – 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