Microsoft Security Advisory CVE-2018-0786: Security Feature Bypass in X509 Certificate Validation

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Microsoft Security Advisory CVE-2018-0786

Security Feature Bypass in X509 Certificate Validation

Executive Summary

Microsoft is releasing this security advisory to provide information about a vulnerability in the open source versions of PowerShell Core 6.0. This advisory also provides guidance on what developers can do to update their scripts and module correctly.

Microsoft is aware of a security vulnerability in the open source versions of PowerShell Core where an attacker could present a certificate that is marked invalid for a specific use, but a .NET Core component uses it for that purpose. This action disregards the Enhanced Key Usage tagging.

The security update addresses the vulnerability by ensuring that .NET Core components completely validate certificates.

System administrators are advised to update their PowerShell Core to version 6.0.1. This version will also address CVE-2018-0764.

Discussion

Please use PowerShell/PowerShell#6031 for discussion of this advisory.
Please use dotnet/corefx#26236 for discussion of the .NET CoreFx aspects this advisory.

Affected Software

The vulnerability affects PowerShell Core prior to version 6.0.1

Advisory FAQ

How do I know if I am affected?

If all of the following are true:

1. Run pwsh -v (if, you cannot launch PowerShell Core using pwsh you are affected). If the reported version starts with 6.0.0, you are affected.
2. You also use one of the .NET assemblies referenced in Microsoft Security Advisory CVE-2018-0786: Security Feature Bypass in X509 Certificate Validation dotnet/announcements#51

How do I update to an unaffected version?

Follow the instructions at Get PowerShell to install the latest version of PowerShell Core.

Other Information

Reporting Security Issues

If you have found a potential security issue in PowerShell Core, please email details to secure@microsoft.com.

Support

You can ask questions about this issue on GitHub in the PowerShell organization. This is located at https://github.com/PowerShell/. The Announcements repo (https://github.com/PowerShell/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue where you can ask questions.

What if the update breaks my script or module?

You can uninstall the newer version of PowerShell Core and install the previous version of PowerShell Core. This should be treated as a temporary measure. Therefore, the script or module should be updated to work with the patched version of PowerShell Core.

External Links

CVE-2018-0786

Revisions

V1.0 (Jan 25, 2018): Advisory published.

Version 1.0
Last Updated 2018-01-25