CriticalCVE-2020-0986

Microsoft Windows Kernel Privilege Escalation Vulnerability (CVE-2020-0986)

Published 09.06.2020In CISA KEV since 03.11.2021Sources: CVE.org

What is affected, what to do

An elevation of privilege vulnerability exists when the Windows kernel fails to properly handle objects in memory, aka 'Windows Kernel Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2020-1237, CVE-2020-1246, CVE-2020-1262, CVE-2020-1264, CVE-2020-1266, CVE-2020-1269, CVE-2020-1273, CVE-2020-1274, CVE-2020-1275, CVE-2020-1276, CVE-2020-1307, CVE-2020-1316.

The vulnerability is being actively exploited; treat it as a priority. 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 eq 10 Version 1803 for 32-bit Systems..10 Version 1803 for 32-bit Systems
Microsoft Windows eq 10 Version 1803 for x64-based Systems..10 Version 1803 for x64-based Systems
Microsoft Windows eq 10 Version 1803 for ARM64-based Systems..10 Version 1803 for ARM64-based Systems
Microsoft Windows eq 10 Version 1809 for 32-bit Systems..10 Version 1809 for 32-bit Systems
Microsoft Windows eq 10 Version 1809 for x64-based Systems..10 Version 1809 for x64-based Systems
Microsoft Windows eq 10 Version 1809 for ARM64-based Systems..10 Version 1809 for ARM64-based Systems
Microsoft Windows eq 10 Version 1709 for 32-bit Systems..10 Version 1709 for 32-bit Systems
Microsoft Windows eq 10 Version 1709 for x64-based Systems..10 Version 1709 for x64-based Systems
Microsoft Windows eq 10 Version 1709 for ARM64-based Systems..10 Version 1709 for ARM64-based Systems
Microsoft Windows eq 10 for 32-bit Systems..10 for 32-bit Systems
Microsoft Windows eq 10 for x64-based Systems..10 for x64-based Systems
Microsoft Windows eq 10 Version 1607 for 32-bit Systems..10 Version 1607 for 32-bit Systems
Microsoft Windows eq 10 Version 1607 for x64-based Systems..10 Version 1607 for x64-based Systems
Microsoft Windows eq 8.1 for 32-bit systems..8.1 for 32-bit systems
Microsoft Windows eq 8.1 for x64-based systems..8.1 for x64-based systems
Microsoft Windows eq RT 8.1..RT 8.1
Microsoft Windows Server eq version 1803 (Core Installation)..version 1803 (Core Installation)
Microsoft Windows Server eq 2019..2019
Microsoft Windows Server eq 2019 (Core installation)..2019 (Core installation)
Microsoft Windows Server eq 2016..2016
Microsoft Windows Server eq 2016 (Core installation)..2016 (Core installation)
Microsoft Windows Server eq 2012..2012
Microsoft Windows Server eq 2012 (Core installation)..2012 (Core installation)
Microsoft Windows Server eq 2012 R2..2012 R2
Microsoft Windows Server eq 2012 R2 (Core installation)..2012 R2 (Core installation)

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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

16.4 %

EPSS score

Elevated — model estimates 10-50% exploitation likelihood.

Source: FIRST EPSS, percentile 97.0

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: 214.24 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: 16.4 %; Elevated — model estimates 10-50% 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: 97.0; 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: 09.06.2020
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: 03.11.2021
CISA assessment (SSVC): Exploitation: active · not automatable · Technical impact: total; Source: CISA Vulnrichment, as of 7 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-787

Response and mitigation

Why act now?

Prioritisation rationale

CVE-2020-0986 is a local privilege escalation to kernel/SYSTEM context. It needs only low privileges, requires no user interaction, and results in a full loss of confidentiality, integrity and availability. It has been publicly documented as a sandbox escape chained with a browser exploit in targeted intrusions. CISA lists no known ransomware use, but exploitation likelihood remains assessed as high. For organisations on current patch levels the residual risk is low. Urgency becomes high wherever out-of-support Windows 10 1709, 1803 or 1809 builds remain, especially on internet-facing or multi-user systems. Under NIS2, track such legacy hosts as a lifecycle risk and retire them promptly.

01
Runbook step 1
Immediate response (0-24 h)
- Verify and deploy the security update: Microsoft fixed CVE-2020-0986 in the June 2020 Patch Tuesday release. Look up the per-build KB in the Microsoft Security Update Guide. Deploy the latest cumulative update rather than stopping at June 2020. Public analyses showed the original fix was incomplete, and the follow-on issue CVE-2021-1648 was only closed in January 2021.
- Inventory out-of-support builds: Identify all hosts running Windows 10 1709, 1803 or 1809 (builds 16299, 17134, 17763) via Intune, SCCM/MECM or Get-ComputerInfo | Select OsBuildNumber. Apart from LTSC and Server variants, these builds no longer receive updates. Schedule a mandatory in-place upgrade to a supported release.
- Handle high-exposure hosts first: Start with terminal servers, VDI hosts, jump hosts, admin workstations and any client running internet-facing browsers or Office. On these hosts, a local privilege escalation is the typical second stage after a browser or document exploit.
- Triage for compromise: On unpatched hosts, hunt for SYSTEM processes with anomalous lineage (see Detection rules). On a hit, isolate the host via EDR and rotate locally cached credentials, especially those of privileged accounts and the local admin password (LAPS).
02
Runbook step 2
Mitigation layers
- Configuration/lifecycle: Microsoft offers no official workaround, so patching is the only durable fix. Until the upgrade is done, treat unsupported builds as elevated-risk assets. Place them in a dedicated segment with tight east-west filtering.
- Endpoint hardening: Enable Microsoft Defender ASR rules, particularly "Block Office applications from creating child processes" and "Block executable content from email client and webmail". Disable Internet Explorer and the MSHTML engine or replace them with Edge, because publicly documented exploit chains paired this flaw with a browser exploit.
- Application control: Run WDAC or AppLocker in enforce mode. Block execution from user-writable paths (%TEMP%, %APPDATA%, Downloads) so that unsigned exploit binaries cannot launch.
- IAM/least privilege: Remove standing local admin rights and roll out LAPS or Windows LAPS. Enable Credential Guard so that gaining SYSTEM does not immediately lead to harvesting domain credentials from LSASS.
- Print subsystem surface: Public analyses place the bug in the 32-bit printer driver host splwow64.exe. On hosts with no printing need, such as servers and jump hosts, disable the Print Spooler and restrict 32-bit print paths. Test the operational impact first.
03
Runbook step 3
Detection rules
- Sysmon EID 1 / Security 4688 – anomalous splwow64 children: splwow64.exe does not spawn shells in normal operation. Sigma shape: ParentImage|endswith: '\splwow64.exe' AND Image|endswith: ['\cmd.exe','\powershell.exe','\rundll32.exe','\mshta.exe'].
- splwow64 lineage: splwow64.exe spawned by a browser (iexplore.exe or renderer processes) and followed by outbound connections (Sysmon EID 3) or file writes to %TEMP% (EID 11). KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "splwow64.exe" and FileName !in~ ("conhost.exe")
- Integrity jump: Processes running at IntegrityLevel = System whose ancestry traces back to a medium- or low-integrity process of an interactive user rather than through services.exe, svchost.exe or winlogon.exe. Query via EDR process-tree analytics or the Sysmon EID 1 IntegrityLevel field.
- Post-escalation follow-on: LSASS access (Sysmon EID 10, TargetImage ending in lsass.exe, GrantedAccess 0x1010/0x1410), new services (System 7045) or scheduled tasks (Security 4698) within minutes of splwow64.exe anomalies.
- Dropped binaries: Sysmon EID 7/11 for unsigned DLLs or EXEs written to user paths shortly before a SYSTEM process launch.

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

Source: NVD (NIST), cvelistv5, CISA KEV Catalog

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 1803 for x64-based Systems` `10 Version 1709 for ARM64-based Systems` `RT 8.1` `10 Version 1809 for ARM64-based Systems` `10 Version 1709 for x64-based Systems` `10 for 32-bit Systems` `8.1 for 32-bit systems` `10 for x64-based Systems` `10 Version 1803 for 32-bit Systems` `10 Version 1607 for 32-bit Systems` `10 Version 1607 for x64-based Systems` `10 Version 1809 for x64-based Systems` `10 Version 1809 for 32-bit Systems` `8.1 for x64-based systems` `10 Version 1709 for 32-bit Systems` `10 Version 1803 for ARM64-based Systems`	— — — — — — — — — — — — — — — —
Microsoft	Windows Server	`2012 R2` `2019` `2012 (Core installation)` `2012` `2012 R2 (Core installation)` `2019 (Core installation)` `2016 (Core installation)` `2016` `version 1803 (Core Installation)`	— — — — — — — — —

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1507	—
Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1709	—
Windows	microsoft	windows_10_1803	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_1903	—
Windows	microsoft	windows_10_1909	—
Windows	microsoft	windows_10_2004	—
Windows	microsoft	windows_8.1	—
Windows	microsoft	windows_rt_8.1	—
Windows	microsoft	windows_server_1803	—
Windows	microsoft	windows_server_1903	—
Windows	microsoft	windows_server_1909	—
Windows	microsoft	windows_server_2004	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2012	—
Windows	microsoft	windows_server_2016	—
Windows	microsoft	windows_server_2019	—

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.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	03.11.2021
Packet Storm	Microsoft Windows splWOW64 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-2020-0986x_refsource_MISC, Patch, Vendor advisory
packetstormsecurity.comfiles/160698/Microsoft-Windows-splWOW64-Privilege-Escalation.ht…x_refsource_MISC, Third-party advisory, Vulnerability database
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0986government-resource, US government resource

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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