How severe is CVE-2021-33739?

CVE-2021-33739 has a CVSS score of 8.4/10, rated HIGH. Immediate patching is strongly recommended.

Which products are affected by CVE-2021-33739?

CVE-2021-33739 affects the following products: microsoft windows 10 20h2, microsoft windows 10 21h1, microsoft windows 10 1909, microsoft windows 10 2004, microsoft windows server 20h2, microsoft windows server 2004.

How do I patch CVE-2021-33739?

Apply the microsoft windows 10 20h2 security patch or hotfix for CVE-2021-33739 on the affected version, following the vendor advisory for your exact build.

How do I detect CVE-2021-33739 across my infrastructure?

Inventory every microsoft windows 10 20h2 deployment and check each version against the affected-products list above.

How do I mitigate CVE-2021-33739 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Is CVE-2021-33739 actively exploited in the wild?

Yes. There are 9 known exploit references for CVE-2021-33739, including 7 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-33739?

CVE-2021-33739 has an EPSS (Exploit Prediction Scoring System) score of 6.6%, placing it in the 94th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2021-33739 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-33739 (Microsoft Desktop Window Manager (DWM) Core Library Privilege Escalation Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2021-11-17. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

Which products and versions are affected by CVE-2021-33739?

CVE-2021-33739 affects microsoft windows 10 20h2; microsoft windows 10 21h1; microsoft windows 10 1909; microsoft windows 10 2004, and 2 more product(s). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-33739 published, and has it been updated?

CVE-2021-33739 was published on June 8, 2021 and was last updated on June 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

CISA KEV · ACTIVELY EXPLOITED

HIGH severity

CVE-2021-33739 — Windows 10 20h2

HIGH

CVE-2021-33739 is a high-severity (CVSS 8.4) vulnerability in microsoft windows 10 20h2. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

Microsoft DWM Core Library Elevation of Privilege Vulnerability

Published

Jun 8, 2021

Updated

Jun 17, 2026

Affected

6 products

Patched

See advisory

Exploits

9 known

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. Federal agencies were required to remediate by 2021-11-17.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-33739.

EPSS Exploitation Probability

via FIRST.org ↗

6.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs94th percentile — riskier than 94% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-33739 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

Microsoft DWM Core Library Elevation of Privilege Vulnerability

Affected Products

6 products · 6 configurations

windows 10 20h2microsoft

< 10.0.19042.1052

range

windows 10 21h1microsoft

< 10.0.19043.1052

range

windows 10 1909microsoft

< 10.0.18363.1621

range

windows 10 2004microsoft

< 10.0.19041.1052

range

windows server 20h2microsoft

< 10.0.19042.1052

range

windows server 2004microsoft

< 10.0.19041.1052

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Microsoft DWM Core Library Elevation of Privilege Vulnerability

portal.msrc.microsoft.comMSJun 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

github.comGithubJun 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

github.comGithubSep 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

github.comGithubJun 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

cisa.govCISANov 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

github.comGithubJun 2021

Microsoft DWM Core Library Elevation of Privilege Vulnerability

github.comGithubSep 2021

Detection & mitigation playbook

Vendor / appliance

Detect
Inventory every microsoft windows 10 20h2 deployment and check each version against the affected-products list above.
Fix
Apply the microsoft windows 10 20h2 security patch or hotfix for CVE-2021-33739 on the affected version, following the vendor advisory for your exact build.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Frequently Asked Questions

Microsoft DWM Core Library Elevation of Privilege Vulnerability

O3 Security · Runtime Protection

Is CVE-2021-33739 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

Protect my workloads How runtime protection works

CVE-2021-33739 — Windows 10 20h2

Exploitation Status

Actively exploited in the wild

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Description

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-33739 being exploited in your environment?