Windows Win32k Elevation of Privilege Vulnerability (CVE-2021-1732)
Published In CISA KEV since Sources: SingCERT, CVE.org
- Actively exploited
- Source: CSA/SingCERT How we classify
- Ransomware
- Public exploit
What is affected, what to do
Windows Win32k Elevation of Privilege Vulnerability
The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Microsoft Windows 10 Version 1803
gte 10.0.0..* - Microsoft Windows 10 Version 1809
gte 10.0.0..* - Microsoft Windows Server 2019
gte 10.0.0..* - Microsoft Windows Server 2019 (Server Core installation)
gte 10.0.0..* - Microsoft Windows 10 Version 1909
gte 10.0.0..* - Microsoft Windows Server, version 1909 (Server Core installation)
gte 10.0.0..* - Microsoft Windows 10 Version 2004
gte 10.0.0..* - Microsoft Windows Server version 2004
gte 10.0.0..* - Microsoft Windows 10 Version 20H2
gte 10.0.0..* - Microsoft Windows Server version 20H2
gte 10.0.0..*
- Microsoft Windows 10 Version 1803
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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: SingCERT, CVE.org
78.4 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.58
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- 243.33 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: CSA/SingCERT 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- 78.4 %
- 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- 99.58
- 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 4 February 2021
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-787
Response and mitigation
Why act now?
Prioritisation rationale
This CVE sits on KEV because local privilege escalation is the second stage in nearly every real-world Windows intrusion — a phishing dropper runs as a standard user, CVE-2021-1732 lifts it to SYSTEM within minutes, and the operator pivots to credential dumping and lateral movement. CISA has flagged known ransomware use, and multiple ransomware loaders embed this primitive. Despite requiring local access (AV:L), any environment with interactive users, VDI, Terminal Servers, or unmitigated user-space RCE exposure should treat this as top urgency; exploitation likelihood is among the highest in the Microsoft catalogue. Headless servers without interactive logons are less exposed but not safe to ignore — any workload with a web-shell or RCE precursor makes this EoP instantly critical.
Runbook step 1
Immediate response (0-24 h)
- Deploy the February 2021 Microsoft cumulative update across all affected hosts: KB4601319 (Windows 10 2004/20H2, Server 2004), KB4601345 (1909, Server 1909), KB4601349 (1809, Server 2019), KB4601354 (1803) — start with Terminal Servers, VDI pools, jump hosts and shared workstations, since the flaw grants local SYSTEM.
- Prioritise by exposure: multi-user hosts and endpoints that run browser or Office workloads for unprivileged users first — those are where initial foothold lands and gets escalated to kernel.
- For hosts that cannot be patched immediately, flip WDAC/AppLocker to enforcement mode to block the loaders typically chained with CVE-2021-1732 as a second stage.
- Rotate local administrator passwords and enforce LAPS if not already in place — LSASS credential dumping is the standard follow-on activity after a successful EoP.
- Switch EDR policy from „audit" to „block" for kernel callback tampering and token-theft signatures; most EDR vendors ship dedicated detections for this callback-based technique.
Runbook step 2
Mitigation layers
- Endpoint hardening: enable Microsoft Defender ASR rules, in particular „Block credential stealing from LSASS" and „Block process creations originating from PSExec and WMI commands" to disrupt the post-exploitation chain.
- Least privilege: no local admin rights for standard users; UAC at „Always notify"; remove users from „Debug programs" and „Load and unload device drivers" privileges.
- Network segmentation: isolate VDI and RDS farms in dedicated VLANs with egress restricted to defined destinations (proxy, AD, update servers); block SMB and WinRM lateral movement between user workstations via host firewall.
- Enable Exploit Guard / HVCI (Memory Integrity) and Credential Guard where hardware supports it — raises the bar for kernel exploits and protects token material in LSA.
- Enforce browser and Office sandboxing (Edge Application Guard, Office Protected View) to catch the initial infection stage before the EoP triggers.
- Monitor for new kernel drivers and WDAC code-integrity violations („Microsoft-Windows-CodeIntegrity/Operational" log) as an early warning signal.
Runbook step 3
Detection rules
- Sysmon Event ID 1 (Process Create) where ParentImage is a browser/Office binary and the child process shortly runs as SYSTEM — pivot via the User SID in the access token (
User=NT AUTHORITY\SYSTEMwhile ParentUser != SYSTEM). - Windows Security Event ID 4688 (new process under user context) followed by 4672 (Special Privileges Assigned) for the same process within seconds — classic EoP pattern.
- Sysmon EID 10 (ProcessAccess) targeting lsass.exe with GrantedAccess 0x1010/0x1410/0x1438 from processes outside the sanctioned admin-tool allow-list — typical follow-on after a successful EoP.
- KQL for Microsoft Defender for Endpoint:
DeviceProcessEvents | where InitiatingProcessAccountName != "SYSTEM" and AccountName == "SYSTEM" and InitiatingProcessParentFileName in~ ("explorer.exe","chrome.exe","msedge.exe","winword.exe","excel.exe"). - Sigma shape: alert on unexpected processes acquiring SeDebugPrivilege or SeTcbPrivilege that are not signed Microsoft binaries (Event ID 4703); in practice the xxxFrameWindow manipulation of this exploit surfaces as unexplained privilege gains.
- Windows Defender Exploit Guard Event ID 1121/1122 (ASR block) as a tripwire for exploitation attempts in the chain.
- Sysmon Event ID 1 (Process Create) where ParentImage is a browser/Office binary and the child process shortly runs as SYSTEM — pivot via the User SID in the access token (
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 Win32k Elevation of Privilege Vulnerability
Source: CSA/SingCERT, CISA KEV Catalog, cvelistv5, NVD (NIST)
Vendors and products
- Microsoft Windows 10 1803
- Microsoft Microsoft Windows 10 1809
- Microsoft Windows 10 1909
- Microsoft Windows 10 2004
- Microsoft Windows 10 20h2
- Microsoft Windows 10 Version 1803
- Microsoft Windows 10 Version 1809
- Microsoft Windows 10 Version 1909
- Microsoft Windows 10 Version 2004
- Microsoft Windows 10 Version 20h2
- Microsoft Windows Server 1909
- Microsoft Microsoft Windows Server 2004
Affected operating systems
| Windows | Microsoft | Windows 10 Version 1803 | — |
| Windows | Microsoft | Windows 10 Version 1809 | — |
| Windows | Microsoft | Windows 10 Version 1909 | — |
| Windows | Microsoft | Windows 10 Version 2004 | — |
| Windows | Microsoft | Windows 10 Version 20H2 | — |
| Windows | Microsoft | Windows Server 2019 | — |
| Windows | Microsoft | Windows Server 2019 (Server Core installation) | — |
| Windows | Microsoft | Windows Server version 2004 | — |
| Windows | Microsoft | Windows Server version 20H2 | — |
| Windows | Microsoft | Windows Server, version 1909 (Server Core installation) | — |
| Windows | microsoft | windows_10_1803 | — |
| Windows | microsoft | windows_10_1809 | — |
| Windows | microsoft | windows_10_1909 | — |
| Windows | microsoft | windows_10_2004 | — |
| Windows | microsoft | windows_10_20h2 | — |
| Windows | microsoft | windows_server_1909 | — |
| Windows | microsoft | windows_server_2004 | — |
| Windows | microsoft | windows_server_2019 | — |
| Windows | microsoft | windows_server_20h2 | — |
Weakness classes (CWE)
CWE-787Out-of-bounds Write
Base
The product writes data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-787
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 | |
| CSA/SingCERT | February 2021 Monthly Patch Release (opens in a new tab)CSA/SingCERT | actively exploited | |
| Packet Storm | Win32k ConsoleControl Offset Confusion (opens in a new tab)packetstormsecurity.com | PoC (publicly reported)reported, not verified | — |
| Packet Storm | Win32k ConsoleControl Offset Confusion Privilege Escalation (opens in a new tab)packetstormsecurity.com | PoC (publicly reported)reported, not verified | — |
References & sources
- portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2021-1732x_refsource_MISC
- packetstormsecurity.comfiles/161880/Win32k-ConsoleControl-Offset-Confusion.htmlx_refsource_MISC
- packetstormsecurity.comfiles/166169/Win32k-ConsoleControl-Offset-Confusion-Privilege-E…x_refsource_MISC
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-1732government-resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-1732"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-1732.svg?lang=en" alt="CVE-2021-1732 – NEOSEC Intel" height="20"></a>