Understanding and Mitigating Windows Speculative Execution Configuration Check Vulnerabilities

Speculative execution vulnerabilities, such as Meltdown, Spectre, L1 Terminal Fault (L1TF), and Microarchitectural Data Sampling (MDS), pose significant security risks to modern CPUs. These vulnerabilities exploit the speculative execution feature of CPUs to access sensitive data across trust boundaries. This blog post will provide an overview of these vulnerabilities, guidance on registry settings, and PowerShell scripts to mitigate the risks.

Overview of Speculative Execution Vulnerabilities
Speculative Execution is a performance optimization technique used by modern CPUs to improve processing speed. The CPU predicts the likely path of a program’s execution and speculatively executes instructions along that path. If the prediction is correct, the speculative execution results are used, otherwise, they are discarded. However, these speculative execution processes can expose sensitive data to malicious actors.

Common Speculative Execution Vulnerabilities

Meltdown (CVE-2017-5754):

Allows attackers to read privileged memory of other processes.

Affects Intel CPUs and some ARM processors.

Spectre (CVE-2017-5753 and CVE-2017-5715):

Exploits branch prediction to access sensitive data.

Affects a wide range of processors, including Intel, AMD, and ARM.

L1 Terminal Fault (L1TF) (CVE-2018-3615, CVE-2018-3620, CVE-2018-3646):

Allows attackers to access Level 1 (L1) data cache.

Primarily affects Intel CPUs.

Microarchitectural Data Sampling (MDS) (CVE-2018-12126, CVE-2018-12130, CVE-2018-12127, CVE-2019-11091):

Leaks data from microarchitectural buffers.

Affects Intel CPUs.

Mitigation Steps

Microsoft has released patches and guidance to mitigate these vulnerabilities. One of the key steps in mitigating speculative execution vulnerabilities involves configuring registry settings.

Registry Settings for Mitigation
Below are the registry settings to enable mitigations for speculative execution vulnerabilities. You need administrative privileges to modify these settings.

Enabling Meltdown and Spectre Mitigations:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:00000003
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:00000003

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\FeatureSettingsOverride]
“Spectre_Mitigation_ControlFlags”=dword:00000000
“FeatureSettingsOverride”=dword:00000003

Enabling L1 Terminal Fault Mitigations:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:0000000E
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:0000000E

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\FeatureSettingsOverride]
“L1TF_Mitigation_ControlFlags”=dword:00000000
“FeatureSettingsOverride”=dword:0000000E

Enabling Microarchitectural Data Sampling Mitigations:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:000000F0
“FeatureSettingsOverride”=dword:00000000
“FeatureSettingsOverrideMask”=dword:000000F0

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\FeatureSettingsOverride]
“MDS_Mitigation_ControlFlags”=dword:00000000
“FeatureSettingsOverride”=dword:000000F0

PowerShell Script for Mitigation Verification

You can use the SpeculationControl PowerShell script provided by Microsoft to verify if your system is protected against these vulnerabilities.

Download the SpeculationControl Script:

You can download the SpeculationControl script from the official Microsoft site or from the PowerShell Gallery:

powershell
Install-Script -Name SpeculationControl
Run the Script to Check Mitigation Status:

Once downloaded, run the script to check your system’s mitigation status:

powershell
.\SpeculationControl.ps1
The script will provide an output indicating whether the mitigations are enabled.

Enable Mitigations Using PowerShell:

You can also use PowerShell to enable the mitigations. Below is an example script to enable Meltdown and Spectre mitigations:

powershell
# Enable Meltdown Mitigations
Set-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management’ -Name ‘FeatureSettingsOverride’ -Value 0
Set-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management’ -Name ‘FeatureSettingsOverrideMask’ -Value 3

# Enable Spectre Mitigations
Set-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\FeatureSettingsOverride’ -Name ‘Spectre_Mitigation_ControlFlags’ -Value 0
Set-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\FeatureSettingsOverride’ -Name ‘FeatureSettingsOverrideMask’ -Value 3

Conclusion
Speculative execution vulnerabilities are a significant security concern, but with the right mitigations, you can protect your systems from potential attacks. It’s essential to stay informed about the latest updates and apply the necessary patches and configurations.

By following the registry settings and PowerShell scripts provided in this blog, you can mitigate the risks associated with Meltdown, Spectre, L1 Terminal Fault, and Microarchitectural Data Sampling vulnerabilities.

If you have any questions or need further assistance, feel free to reach out. Stay safe and secure!