Description of the Security Only update for .NET Framework 3.5.1 for Windows 7 SP1 and Windows Server 2008 R2 SP1 (KB 4054176)

Summary

This security update resolves a security feature bypass vulnerability that exists when Microsoft .NET Framework and .NET Core components do not completely validate certificates. This security update addresses the vulnerability by helping to make sure that .NET Framework and .NET Core components completely validate certificates. To learn more about this vulnerability, see Microsoft Common Vulnerabilities and Exposures CVE-2018-0786.

Additionally, this security update resolves a Denial of Service vulnerability that exists when .NET Framework and .NET core components improperly process XML documents. This update addresses the vulnerability by correcting how .NET Framework and .NET Core component applications handle XML document processing. To learn more about this vulnerability, see Microsoft Common Vulnerabilities and Exposures CVE-2018-0764.

Important

• If you install a language pack after you install this update, you must reinstall this update. Therefore, we recommend that you install any language packs that you need before you install this update. For more information, see Add language packs to Windows.

Additional information about this security update

• Enhanced Key Usage (EKU) is described in RFC 5280 in section 4.2.1.12. This extension indicates one or more purposes for which the certified public key may be used, in addition to or instead of the basic purposes that are indicated in the key usage extension. For example, a certificate that is used for the authentication of a client to a server must be configured for Client Authentication. Similarly, a certificate that is used for the authentication of a server must be configured for Server Authentication. With this change, besides requiring the appropriate client/server EKU on certificates, if the root certificate is disabled, the certificate chain validation will fail.
  
  When certificates are used for authentication, the authenticator examines the certificate that is provided by the remote endpoint and seeks the correct purpose object identifier in Application Policies extensions. When a certificate is used for client authentication, the object identifier for Client Authentication must be present in the EKU extensions of the certificate, or authentication fails. The object identifier for Client Authentication is 1.3.6.1.5.5.7.3.2. Likewise, when a certificate is used for server authentication, the object identifier for Server Authentication must be present in the EKU extensions of the certificate, or authentication fails. The object identifier for Server Authentication is 1.3.6.1.5.5.7.3.1. Certificates that have no EKU extension continue to authenticate correctly.
  
  First, consider making changes to your component’s certificates to make sure that they are using the correct EKU OID attributes and are secured correctly. If you temporarily cannot access correctly reissued certificates, you can choose to opt in or out of the security change to avoid any connectivity effects. To do this, specify the following appsetting in the configuration file:

  <appSettings>
      <add key="wcf:useLegacyCertificateUsagePolicy" value="true" />
  </appSettings>

  Note Setting the value to “true” will opt out of the security changes.

• For more information about this security update as it relates to Windows 7 Service Pack 1 (SP1) and Windows Server 2008 R2 SP1, see the following article in the Microsoft Knowledge Base:

4055269 Security Only update for .NET Framework 3.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, and 4.7.1 updates for Windows 7 SP1 and Windows Server 2008 R2 SP1 (KB 4055269)

How to obtain and install the update

File information

File hash

File attributes

The English (United States) version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and times for these files are listed in Coordinated Universal Time (UTC). The dates and times for these files on your local computer are displayed in your local time together with your current daylight-saving time (DST) bias. Additionally, the dates and times may change when you perform certain operations on the files.

For all x86-based systems

For all x64-based systems

For all IA64-based ystems

How to obtain help and support for this security update

• Help for installing updates: Windows Update FAQ

• Security solutions for IT professionals: TechNet Security Support and Troubleshooting

• Help for protecting your Windows-based products and services from viruses and malware: Microsoft Secure

• Local support according to your country: International Support

Applies to

This article applies to the following:

• Microsoft .NET Framework 3.5.1 when used with:

  • Windows Server 2008 R2 Service Pack 1

  • Windows 7 Service Pack 1