# CVE-2018-8435: Windows Hyper-V Security Feature Bypass Vulnerability

CVE-2018-8435 is fixed in 9 products on 1 platform, first by KB4457131, released September 11, 2018. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2018-8435
- Priority: Routine
- CVSS: 4.2 (Important)
- EPSS: 0.0136
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Less Likely
- Published: Sep 11, 2018
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2018-8435

## Description

<p>A security feature bypass vulnerability exists when Windows Hyper-V BIOS loader fails to provide a high-entropy source.</p> <p>To exploit this vulnerability, an attacker would need to reboot a guest virtual machine numerous times until the vulnerability is triggered.</p> <p>The security update addresses the vulnerability by correcting security feature behavior to ensure Windows Hyper-V BIOS loader provides a high-entropy source.</p>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Windows 10 Version 1607 for x64-based Systems | 14393.2485 | [KB4457131](https://patchblox.com/security/data/fix/microsoft/kb4457131.md) | Sep 11, 2018 |
| Microsoft | Windows 10 Version 1703 for x64-based Systems | 15063.1324 | [KB4457138](https://patchblox.com/security/data/fix/microsoft/kb4457138.md) | Sep 11, 2018 |
| Microsoft | Windows 10 Version 1709 for x64-based Systems | 16299.665 | [KB4457142](https://patchblox.com/security/data/fix/microsoft/kb4457142.md) | Sep 11, 2018 |
| Microsoft | Windows 10 Version 1803 for x64-based Systems | 17134.285 | [KB4457128](https://patchblox.com/security/data/fix/microsoft/kb4457128.md) | Sep 11, 2018 |
| Microsoft | Windows 10 for x64-based Systems | 10240.17976 | [KB4457132](https://patchblox.com/security/data/fix/microsoft/kb4457132.md) | Sep 11, 2018 |
| Microsoft | Windows Server 2016 | 14393.2485 | [KB4457131](https://patchblox.com/security/data/fix/microsoft/kb4457131.md) | Sep 11, 2018 |
| Microsoft | Windows Server 2016 (Server Core installation) | 14393.2485 | [KB4457131](https://patchblox.com/security/data/fix/microsoft/kb4457131.md) | Sep 11, 2018 |
| Microsoft | Windows Server, version 1709  (Server Core Installation) | 16299.665 | [KB4457142](https://patchblox.com/security/data/fix/microsoft/kb4457142.md) | Sep 11, 2018 |
| Microsoft | Windows Server, version 1803  (Server Core Installation) | 17134.285 | [KB4457128](https://patchblox.com/security/data/fix/microsoft/kb4457128.md) | Sep 11, 2018 |

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Data as of 2026-11-07T12:40:37Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo