Windows Event Tracing Elevation of Privilege Vulnerability (CVE-2021-34486)
Published Last modified In CISA KEV since Sources: CVE.org
What is affected, what to do
Windows Event Tracing Elevation of Privilege Vulnerability
The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1809 to version 10.0.17763.2114, Microsoft Windows 10 Version 1909 to version 10.0.18363.1734, Microsoft Windows 10 Version 2004 to version 10.0.19041.1165. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Microsoft Windows 10 Version 1809
lt 10.0.17763.0..10.0.17763.2114 - Microsoft Windows 10 Version 1909
lt 10.0.0..10.0.18363.1734 - Microsoft Windows 10 Version 2004
lt 10.0.0..10.0.19041.1165 - Microsoft Windows 10 Version 20H2
lt 10.0.0..10.0.19042.1165 - Microsoft Windows 10 Version 21H1
lt 10.0.0..10.0.19043.1165 - Microsoft Windows Server 2019
lt 10.0.17763.0..10.0.17763.2114 - Microsoft Windows Server 2019 (Server Core installation)
lt 10.0.17763.0..10.0.17763.2114 - Microsoft Windows Server version 2004
lt 10.0.0..10.0.19041.1165 - Microsoft Windows Server version 20H2
lt 10.0.0..10.0.19042.1165
- Microsoft Windows 10 Version 1809
- Fixed in
- Microsoft Windows 10 Version 1809
10.0.17763.2114 - Microsoft Windows 10 Version 1909
10.0.18363.1734 - Microsoft Windows 10 Version 2004
10.0.19041.1165 - Microsoft Windows 10 Version 20H2
10.0.19042.1165 - Microsoft Windows 10 Version 21H1
10.0.19043.1165 - Microsoft Windows Server 2019
10.0.17763.2114 - Microsoft Windows Server 2019 (Server Core installation)
10.0.17763.2114 - Microsoft Windows Server version 2004
10.0.19041.1165 - Microsoft Windows Server version 20H2
10.0.19042.1165
- 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: CVE.org
9.3 %
EPSS score
Moderate — model estimates 1-10% exploitation likelihood.
Source: FIRST EPSS, percentile 95.4
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- 211.75 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 exploited
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- 9.3 %
- 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- 95.4
- 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 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
This Windows Event Tracing flaw is a textbook local privilege escalation: it needs existing low-privileged code execution but no user interaction, and it yields full host compromise. That makes it the natural second stage after phishing, a browser exploit or stolen credentials. Exploitation likelihood is high and sits in the upper tier of all CVEs, though CISA does not flag known ransomware use. For estates on current patch levels this is already closed by routine cumulative updates. The real exposure is EoS Windows 10 builds, terminal servers and shared hosts that have drifted, and those should be remediated first within your NIS2 timelines for known-exploited vulnerabilities.
Runbook step 1
Immediate response (0-24 h)
- Build inventory: Enumerate all Windows 10 1809/1909/2004/20H2/21H1, Windows Server 2019 (including Server Core) and Windows Server version 2004 hosts and compare their OS builds against the fixed builds. Anything below 10.0.17763.2114 (1809/Server 2019), 10.0.18363.1734 (1909), or 10.0.19041.1165 / 10.0.19042.1165 / 10.0.19043.1165 (2004/20H2/21H1) is vulnerable. Quick check:
Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' | Select CurrentBuild, UBR. - Patch deployment: Deploy the Microsoft cumulative security update that brings each host to at least those builds. Look up the per-version KB ID in the Microsoft Security Update Guide entry for CVE-2021-34486. Because updates are cumulative, any current rollup includes the fix.
- Patch order: Start with multi-user systems (RDS/terminal servers, VDI, Citrix), jump hosts/PAWs, build servers and any host where contractors hold local accounts. On these systems, a low-privileged local attacker is a normal day.
- End-of-service systems: Treat Windows 10 1809 (client), 1909, 2004, 20H2, 21H1 and Server version 2004 as high risk, since they no longer receive updates. Migrate them to a supported release, or isolate them from production networks until you can.
- Compromise assumption: On unpatched hosts with a known initial-access event (phishing, malware detection), assume escalation to SYSTEM has already happened. Rotate local admin and service account passwords (LAPS) and invalidate cached privileged credentials.
- Build inventory: Enumerate all Windows 10 1809/1909/2004/20H2/21H1, Windows Server 2019 (including Server Core) and Windows Server version 2004 hosts and compare their OS builds against the fixed builds. Anything below 10.0.17763.2114 (1809/Server 2019), 10.0.18363.1734 (1909), or 10.0.19041.1165 / 10.0.19042.1165 / 10.0.19043.1165 (2004/20H2/21H1) is vulnerable. Quick check:
Runbook step 2
Mitigation layers
- No vendor workaround: Microsoft documents no configuration workaround, so the update is the only full fix. The controls below reduce likelihood and blast radius only.
- Application control: Use WDAC or AppLocker to block unsigned binaries from user-writable paths (
%TEMP%,%APPDATA%,%LOCALAPPDATA%,C:\Users\Public, Downloads). Local exploits are usually dropped there as a custom EXE/DLL. - Attack surface reduction: Enable Defender ASR rules, particularly "Block executable files unless they meet a prevalence, age, or trusted list criterion" and "Block process creations originating from PSExec and WMI commands". Enable Credential Guard and LSA protection (RunAsPPL) to hinder credential dumping once SYSTEM is reached.
- IAM/least privilege: Restrict interactive and RDP logon on servers to admin groups (GPO "Allow log on locally/through Remote Desktop Services"). Enforce admin tiering so Tier-0 accounts never log on to unpatched Tier-1/2 hosts.
- Network segmentation: Move unpatched and EoS hosts into a dedicated VLAN and block SMB (445), RDP (3389), WinRM (5985/5986) and RPC (135) from there towards server and DC segments. This limits lateral movement after a local escalation.
- EDR resilience: Enforce Tamper Protection. Attackers holding SYSTEM commonly disable ETW providers and security sensors.
Runbook step 3
Detection rules
- Integrity jump (EDR/Sysmon EID 1): A System-integrity process whose parent runs at Medium/Low and is not a known broker (consent.exe, services.exe, svchost.exe). KQL:
DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel in ("Medium","Low") and InitiatingProcessFileName !in~ ("consent.exe","services.exe","svchost.exe") - Execution from user paths (Sysmon EID 1 / Security 4688): An unsigned binary in
\AppData\,\Temp\or\Users\Public\spawnscmd.exe/powershell.exeasNT AUTHORITY\SYSTEM. Sigma shape:selection: Image|contains: ['\AppData\','\Temp\'] AND User|contains: 'SYSTEM'. - Post-escalation persistence: System 7045 or Security 4697 (new service), plus 4720/4732 (new local account or added to Administrators), shortly after a standard-user logon (4624, Logon Type 2/10) on the same host. SPL:
index=wineventlog (EventCode=7045 OR EventCode=4732) | transaction host maxspan=30m - ETW tampering and instability: Events in the Microsoft-Windows-Kernel-EventTracing channel (session stopped/modified),
logman stop/logman updateon command lines, and bugchecks (System EID 1001/41) on endpoints. Failed kernel exploitation frequently crashes the host. - Follow-on activity: Access to
lsass.exewith suspicious GrantedAccess masks (Sysmon EID 10, e.g. 0x1010, 0x1FFFFF) by non-system processes immediately after an integrity jump.
- Integrity jump (EDR/Sysmon EID 1): A System-integrity process whose parent runs at Medium/Low and is not a known broker (consent.exe, services.exe, svchost.exe). KQL:
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 Event Tracing Elevation of Privilege Vulnerability
Source: CISA KEV Catalog, NVD (NIST), cvelistv5, 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 1909 |
|
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| Microsoft | Windows 10 Version 2004 |
|
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| Microsoft | Windows 10 Version 20H2 |
|
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| Microsoft | Windows 10 Version 21H1 |
|
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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 version 2004 |
|
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| Microsoft | Windows Server version 20H2 |
|
|
Vendors and products
- Microsoft Microsoft Windows 10 1809
- Microsoft Windows 10 1909
- Microsoft Windows 10 2004
- Microsoft Windows 10 20h2
- Microsoft Windows 10 21h1
- Microsoft Windows 10 Version 1809
- Microsoft Windows 10 Version 1909
- Microsoft Windows 10 Version 2004
- Microsoft Windows 10 Version 20h2
- Microsoft Windows 10 Version 21h1
- Microsoft Microsoft Windows Server 2004
- Microsoft Microsoft Windows Server 2019
Affected operating systems
| Windows | microsoft | windows_10_1809 | 10.0.17763.2114 |
| Windows | microsoft | windows_10_1809 | 10.0.18363.1734 |
| Windows | microsoft | windows_10_1809 | 10.0.19041.1165 |
| Windows | microsoft | windows_10_1809 | — |
| Windows | microsoft | windows_10_1909 | 10.0.18363.1734 |
| Windows | microsoft | windows_10_1909 | — |
| Windows | microsoft | windows_10_2004 | — |
| Windows | microsoft | windows_10_20H2 | 10.0.19042.1165 |
| Windows | microsoft | windows_10_20h2 | — |
| Windows | microsoft | windows_10_21H1 | 10.0.19043.1165 |
| Windows | microsoft | windows_10_21h1 | — |
| Windows | microsoft | windows_server_2004 | 10.0.19041.1165 |
| Windows | microsoft | windows_server_2004 | — |
| Windows | microsoft | windows_server_2019 | 10.0.17763.2114 |
| Windows | microsoft | windows_server_2019 | — |
| Windows | microsoft | windows_server_20H2 | 10.0.19042.1165 |
| Windows | microsoft | windows_server_20h2 | — |
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
- portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2021-34486x_refsource_MISC, x_transferred
- Microsoft Security Update GuideWindows Event Tracing Elevation of Privilege VulnerabilityVendor advisory, Patch
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34486government-resource
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).
NVD analysis modifiedNVD
Show the original change
Individual changes of this event as published by NVD Type Action Before After Reference type added —Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34486 Types: Patch, Vendor AdvisorySource identifier: nvd@nist.gov
Record modifiedMicrosoft
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34486Reference removed https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34486—Reference type removed https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34486 Types: Patch, Vendor Advisory—Affected versions (publisher) changed Windows 10 Version 1809, Windows Server 2019, Windows Server 2019 (Server Core installation) (+6)Windows 10 Version 1809, Windows 10 Version 1809, Windows 10 Version 1909 (+7)Source identifier: secure@microsoft.com
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-34486"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-34486.svg?lang=en" alt="CVE-2021-34486 – NEOSEC Intel" height="20"></a>