Microsoft HTTP Protocol Stack Remote Code Execution
CVE-2021-31166 is a critical-severity use after free vulnerability in Windows 10 Version 2004 from Microsoft, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 10.0.19041.982 as the first without the flaw, so updating Windows 10 Version 2004 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on April 6, 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 2004 to 10.0.19041.982 or a later version.
- Update Windows Server version 2004 to 10.0.19041.982 or a later version.
- Update Windows 10 Version 20H2 to 10.0.19042.982 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.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 2004 | 10.0.0 up to, but not including, 10.0.19041.982 | 10.0.19041.982 |
| Microsoft | Windows Server version 2004 | 10.0.0 up to, but not including, 10.0.19041.982 | 10.0.19041.982 |
| Microsoft | Windows 10 Version 20H2 | 10.0.0 up to, but not including, 10.0.19042.982 | 10.0.19042.982 |
| Microsoft | Windows Server version 20H2 | 10.0.0 up to, but not including, 10.0.19042.982 | 10.0.19042.982 |
| Microsoft | Windows 10 2004 | before 10.0.19041.982 | 10.0.19041.982 |
| Microsoft | Windows 10 20h2 | before 10.0.19042.982 | 10.0.19042.982 |
| Microsoft | Windows Server 2004 | before 10.0.19041.982 | 10.0.19041.982 |
| Microsoft | Windows Server 20h2 | before 10.0.19042.982 | 10.0.19042.982 |
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
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- 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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CNA (microsoft.com) |
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 2.0 | 7.5 | High | NVD |
Official description
HTTP Protocol Stack Remote Code Execution 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: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.htmlThird Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31166US Government Resource
Other vulnerabilities in Windows 10 Version 2004
- 7.8 High severity
Microsoft Windows Privilege Escalation Exploited
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Microsoft Win32k Privilege Escalation Exploited
- 7.8 High severity
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Microsoft MSHTML Remote Code Execution Exploited
Recent Use After Free vulnerabilities
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Google Chromium Blink Use-After-Free Exploited
- 10.0 Critical severity
- 4.4 Medium severity
Samsung Mobile Devices Memory Corruption Exploited
- 8.8 High severity
Google Chromium Blink Use-After-Free Exploited
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