Microsoft Desktop Window Manager (DWM) Core Library Privilege Escalation
CVE-2021-33739 is a high-severity vulnerability in Windows 10 Version 1909 from Microsoft, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 10.0.18363.1621 as the first without the flaw, so updating Windows 10 Version 1909 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Windows 10 Version 1909 to 10.0.18363.1621 or a later version.
- Update Windows 10 Version 21H1 to 10.0.19043.1052 or a later version.
- Update Windows 10 Version 2004 to 10.0.19041.1052 or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on portal.msrc.microsoft.com for workarounds and exact fixed builds.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 1909 | 10.0.0 up to, but not including, 10.0.18363.1621 | 10.0.18363.1621 |
| Microsoft | Windows 10 Version 21H1 | 10.0.0 up to, but not including, 10.0.19043.1052 | 10.0.19043.1052 |
| Microsoft | Windows 10 Version 2004 | 10.0.0 up to, but not including, 10.0.19041.1052 | 10.0.19041.1052 |
| Microsoft | Windows Server version 2004 | 10.0.0 up to, but not including, 10.0.19041.1052 | 10.0.19041.1052 |
| Microsoft | Windows 10 Version 20H2 | 10.0.0 up to, but not including, 10.0.19042.1052 | 10.0.19042.1052 |
| Microsoft | Windows Server version 20H2 | 10.0.0 up to, but not including, 10.0.19042.1052 | 10.0.19042.1052 |
| Microsoft | Windows 10 1909 | before 10.0.18363.1621 | 10.0.18363.1621 |
| Microsoft | Windows 10 2004 | before 10.0.19041.1052 | 10.0.19041.1052 |
| Microsoft | Windows 10 20h2 | before 10.0.19042.1052 | 10.0.19042.1052 |
| Microsoft | Windows 10 21h1 | before 10.0.19043.1052 | 10.0.19043.1052 |
| Microsoft | Windows Server 2004 | before 10.0.19041.1052 | 10.0.19041.1052 |
| Microsoft | Windows Server 20h2 | before 10.0.19042.1052 | 10.0.19042.1052 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.4 | High | CNA (microsoft.com) |
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 2.0 | 4.6 | Medium | NVD |
Official description
Microsoft DWM Core Library Elevation of Privilege Vulnerability
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33739US Government Resource
Other vulnerabilities in Windows 10 Version 1909
- 5.9 Medium severity
Microsoft Windows LSA Spoofing Exploited
- 9.0 High severity
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