Microsoft Windows Event Tracing Privilege Escalation
CVE-2021-34486 is a high-severity use after free vulnerability in Windows 10 Version 1809 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 attacker with a low-privileged account, without any action from a user. The record lists version 10.0.17763.2114 as the first without the flaw, so updating Windows 10 Version 1809 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on March 28, 2022, 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 1809 to 10.0.17763.2114 or a later version.
- Update Windows 10 Version 1909 to 10.0.18363.1734 or a later version.
- Update Windows 10 Version 2004 to 10.0.19041.1165 or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 1809 | 10.0.17763.0 up to, but not including, 10.0.17763.2114; 10.0.0 up to, but not including, 10.0.17763.2114 | 10.0.17763.2114 |
| Microsoft | Windows 10 Version 1909 | 10.0.0 up to, but not including, 10.0.18363.1734 | 10.0.18363.1734 |
| Microsoft | Windows 10 Version 2004 | 10.0.0 up to, but not including, 10.0.19041.1165 | 10.0.19041.1165 |
| Microsoft | Windows 10 Version 20H2 | 10.0.0 up to, but not including, 10.0.19042.1165 | 10.0.19042.1165 |
| Microsoft | Windows 10 Version 21H1 | 10.0.0 up to, but not including, 10.0.19043.1165 | 10.0.19043.1165 |
| Microsoft | Windows Server 2019 | 10.0.17763.0 up to, but not including, 10.0.17763.2114 | 10.0.17763.2114 |
| Microsoft | Windows Server 2019 (Server Core installation) | 10.0.17763.0 up to, but not including, 10.0.17763.2114 | 10.0.17763.2114 |
| Microsoft | Windows Server version 2004 | 10.0.0 up to, but not including, 10.0.19041.1165 | 10.0.19041.1165 |
| Microsoft | Windows Server version 20H2 | 10.0.0 up to, but not including, 10.0.19042.1165 | 10.0.19042.1165 |
| Microsoft | Windows 10 1809 | before 10.0.17763.2114 | 10.0.17763.2114 |
| Microsoft | Windows 10 1909 | before 10.0.18363.1734 | 10.0.18363.1734 |
| Microsoft | Windows 10 2004 | before 10.0.19041.1165 | 10.0.19041.1165 |
| Microsoft | Windows 10 20h2 | before 10.0.19042.1165 | 10.0.19042.1165 |
| Microsoft | Windows 10 21h1 | before 10.0.19043.1165 | 10.0.19043.1165 |
| Microsoft | Windows Server 2004 | before 10.0.19041.1165 | 10.0.19041.1165 |
| Microsoft | Windows Server 20h2 | before 10.0.19042.1165 | 10.0.19042.1165 |
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
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- 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:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA (microsoft.com) |
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 2.0 | 4.6 | Medium | NVD |
Official description
Windows Event Tracing Elevation of Privilege Vulnerability
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
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.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
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
Advisories
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34486US Government Resource
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