CVE-2020-17087Exploited in the wildNVD status: Analyzed
Microsoft Windows Kernel Privilege Escalation
CVE-2020-17087 is a high-severity incorrect calculation of buffer size vulnerability in Windows 10 Version 1803 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 publication as the first without the flaw, so updating Windows 10 Version 1803 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.
Patch now
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Windows 10 Version 1803 to publication or a later version.
- Update Windows 10 Version 1809 to publication or a later version.
- Update Windows Server 2019 to publication 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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 1803 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1809 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2019 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2019 (Server Core installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1909 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server, version 1909 (Server Core installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for 32-bit Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for x64-based Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for ARM64-based Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server, version 1903 (Server Core installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 2004 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server version 2004 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 20H2 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server version 20H2 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1507 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1607 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2016 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2016 (Server Core installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 7 | 6.1.0 up to, but not including, publication | publication |
| Microsoft | Windows 7 Service Pack 1 | 6.1.0 up to, but not including, publication | publication |
| Microsoft | Windows 8.1 | 6.3.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2008 Service Pack 2 | 6.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2008 Service Pack 2 (Server Core installation) | 6.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2008 R2 Service Pack 1 | 6.1.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2008 R2 Service Pack 1 (Server Core installation) | 6.0.0 up to, but not including, publication | publication |
Version data comes from the organisation that assigned the CVE; 14 further products are omitted here. 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 | 7.2 | High | NVD |
Official description
Windows Kernel Local Elevation of Privilege Vulnerability
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Calculation of Buffer Size
The product does not correctly calculate the size to be used when allocating a buffer.
How developers prevent this class of flaw
- When allocating a buffer for the purpose of transforming, converting, or encoding an input, allocate enough memory to handle the largest possible encoding. For example, in a routine that converts & characters to & for HTML entity encoding, the output buffer needs to be at least 5 times as large as the input buffer.
- Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, not-a-number calculations, and how the language handles numbers that are too large or too small for its underlying representation. Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.
- Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
More Incorrect Calculation of Buffer Size vulnerabilities (CWE-131)
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-2020-17087US Government Resource
Other vulnerabilities in Windows 10 Version 1803
- 7.8 High severity
Microsoft Win32k Privilege Escalation Exploited
- 7.8 High severity
Microsoft Win32k Privilege Escalation Exploited
- 5.5 Medium severity
Microsoft Windows Spoofing Exploited
- 7.8 High severity
Microsoft Win32k Privilege Escalation Exploited
- 7.8 High severity
- 7.8 High severity
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