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Description of the Security Only update for the .NET Framework 4.5.2 for Windows 8.1 and Windows Server 2012 R2: May 9, 2017


This security update for the Microsoft .NET Framework resolves a security feature bypass vulnerability in which the .NET Framework (and the .NET Core) components don't completely validate certificates. To learn more about this vulnerability, see Microsoft Common Vulnerabilities and Exposures CVE-2017-0248.

This update also contains security-enhancing fixes to the Windows Presentation Framework PackageDigitalSignatureManager component's ability to sign packages with the SHA256 hash algorithm.

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  • All future security and nonsecurity updates for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 require update 2919355 to be installed. We recommend that you install update 2919355 on your Windows RT 8.1-based, Windows 8.1-based, or Windows Server 2012 R2-based computer so that you receive future updates.
  • 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.

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Additional information about this security update

  • Enhanced Key Usage (EKU) is described in RFC 5280 in section This extension indicates one or more purposes for which the certified public key may be used, in addition to or in place of the basic purposes that are indicated in the key usage extension. For example, a certificate that’s used for the authentication of a client to a server must be configured for Client Authentication. Similarly, a certificate that’s used for the authentication of a server must be configured for Server Authentication.

    When certificates are used for authentication, the authenticator examines the client certificate and seeks the correct purpose object identifier in Application Policies extensions. For example, the object identifier for Client Authentication is When a certificate is used for client authentication, this object identifier must be present in the EKU extensions of the certificate or authentication fails. Certificates that have no EKU extension continue to authenticate correctly.

    If you temporarily can’t access correctly reissued certificates, you can choose to opt in or out of the security change across all computer operations to avoid any connectivity effects. To do this, specify the following registry key settings, depending on which .NET Framework version your application is targeting.

    Method 1: Updating registry key (available for all versions)

    Note This registry entry must be a DWORD entry.
    • For 32-bit process on 32-bit system and 64-bit process on 64-bit system:
    • For 32-bit process on 64-bit system:
      HKEY_LOCAL_MACHINE \Software\Wow6432Node\Microsoft\.NETFramework\v4.0.30319@RequireCertificateEKUs=0
    You can also opt out on a per-application basis. The following options are available for disabling this change to make sure that application compatibility is maintained.

    Method 2: Disable the policy for individual applications

    Note This registry entry must be a DWORD entry. The only valid value is 0. Any other value is ignored.
    • For 32-bit process on 32-bit system and 64-bit process on 64-bit system:
    • For 32-bit process on 64-bit system:
      HKEY_LOCAL_MACHINE \Software\Wow6432Node\Microsoft\.NETFramework\v4.0.30319@System.Net.ServicePointManager.RequireCertificateEKUs
    Method 3: Using configuration API (available for the .NET Framework 4.6 and later versions)

    Starting in the .NET Framework 4.6, you can change the configuration at an application level through code, an application configuration, or registry changes.

    Configuring the switch in the .NET Framework 4.6

    Note The following examples disable the security feature.
    • Programmatically

      The first thing that the application should do is to run the following code. This is because Service Point Manager initializes only one time.

      private const string DisableCachingName = @"TestSwitch.LocalAppContext.DisableCaching";
      private const string DontCheckCertificateEKUsName= @"Switch.System.Net.DontCheckCertificateEKUs";
      AppContext.SetSwitch(DisableCachingName, true);
      AppContext.SetSwitch(DontCheckCertificateEKUsName, true);
    • Application configuration

      To change the application configuration, add the following entry:

      <AppContextSwitchOverrides value="Switch.System.Net.DontCheckCertificateEKUsName=true"/>
    • Registry key (machine global):

      Registry location: HKEY_LOCAL_MACHINE\Software\[Wow6432Node\]Microsoft\.NETFramework\AppContext\Switch.System.Net.DontCheckCertificateEKUsName

      Type: String
      Value: "true"

    Note By default, Switch.System.Net.DontCheckCertificateEKUsName = True for all .NET Framework 4.x applications that are running on the .NET Framework 4.6 and later versions.
  • For more information about this security update as it relates to Windows 8.1 and Windows Server 2012 R2, see the following article in the Microsoft Knowledge Base:

    4019111 Security Only update for the .NET Framework 3.5 Service Pack 1, 4.5.2, 4.6, 4.6.1, and 4.6.2 updates for Windows 8.1 and Windows Server 2012 R2: May 9, 2017

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How to obtain and install the update

Method 1: Microsoft Update Catalog

To get the stand-alone package for this update, go to the Microsoft Update Catalog

Method 2: Windows Software Update Services (WSUS)

On your WSUS server, follow these steps:

  1. Click Start, click Administrative Tools, and then click Microsoft Windows Server Update Services 3.0.
  2. Expand ComputerName, and then click Action.
  3. Click Import Updates.
  4. WSUS will open a browser window in which you may be prompted to install an ActiveX control. You must install the ActiveX control to continue.
  5. Once the control is installed, you will see the Microsoft Update Catalog screen. Enter 4019111 in the Search box, and then click Search.
  6. Locate the .NET Framework packages that match the operating systems, languages, and processors in your environment. Click Add to add them to your basket.
  7. When you have selected all the packages you need, click View Basket.
  8. Click Import to import the packages to your WSUS server.
  9. Click Close once the packages have been imported to return to WSUS.

The updates are now available for installation through WSUS.

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Update deployment information

For deployment details for this security update, go to the following article in the Microsoft Knowledge Base:

20170509 Security update deployment information: May 9, 2017

Update removal information

Note We do not recommend that you remove any security update. To remove this update, use the Programs and Features item in Control Panel.

Update restart information

This update does not require a system restart after you apply it unless files that are being updated are locked or are being used.

Update replacement information

This update does not replace any previously released update.

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File information

File hash
Package Name Package Hash SHA 1 Package Hash SHA 2
Windows8.1-KB4014595-x64.msu 93FC2B2F2D31FFA069CE4A2CB4CCBC88AC1299F5 EDA1B2B05456B1ABDA775174792A2EF0CB605ABE1B9D8827E309A44F5DCE38EB
Windows8.1-KB4014595-x86.msu 3B23D657716C3C77CA26D7BD89BEE2552BC69AD6 404040BA3D9165D5CB64C5303D84685A1E46A1C531C6269D3CB7FC22A56CCC3F



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How to obtain help and support for this security update

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Applies to

This article applies to the following:
  • Microsoft .NET Framework 4.5.2 when used with:
    • Windows Server 2012 R2
    • Windows 8.1

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Keywords: kbsurveynew, kbsecvulnerability, kbsecurity, kbsecreview, kbsecbulletin, kbbug, kblangall, kbfix, kbexpertiseinter, kb, atdownload, kbmustloc

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Article Info
Article ID : 4014595
Revision : 18
Created on : 5/12/2017
Published on : 5/13/2017
Exists online : False
Views : 270