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SSL/TLS client certificate authentication does not work in Windows 8 or Windows Server 2012

Consider the following scenario:
  • You use the Secure Sockets Layer/Transport Layer Security (SSL/TLS) client certificate authentication on a computer that is running Windows 8 or Windows Server 2012.
  • An operation that is seemingly unrelated to the SSL/TLS client certificate authentication is performed. However, the operation causes the Trusted Root store to exceed the 16 kilobytes (KB) limit. For example, one of the following operations is performed:
    • In a remote session, an unauthenticated user probes the SSL endpoint server by using a client certificate that chains to novel trusted roots. Then, the Cryptographic Application Programming Interface (CAPI) installs the novel trusted roots automatically.
    • A user logs on to the computer and browses an SSL/TLS website that is secured by a novel trusted root.
    • CAPI updates an existing installed root automatically. This behavior causes the size of the root to increase or the enumeration order to change.
    • A change occurs in the certificate enumeration order code (for example, you install a hotfix that changes the certificate store code or changes table sorting).
    • A user switches using certificates.
    • An administrator installs new certificates to the Trusted Root store.
In this scenario, the client certificate authentication no longer works.

Note This issue occurs regardless of the value of the SendTrustedIssuerList registry entry. In other words, you cannot resolve this issue by setting a value for the SendTrustedIssuerList registry entry. The SendTrustedIssuerList registry entry is located under the following registry subkey:
This issue occurs because the trusted root certification authorities list is truncated incorrectly on the server-side. By default, the server does not send the list to the client-side during client certificate validation. Therefore, the truncation is not required.
This hotfix is also available at Microsoft Update Catalog.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix Download Available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft website: Note The "Hotfix Download Available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


To apply this hotfix, you must be running Windows 8 or Windows Server 2012.

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The global version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the 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 the times may change when you perform certain operations on the files.
Windows 8 and Windows Server 2012 file information notes
Important Windows 8 hotfixes and Windows Server 2012 hotfixes are included in the same packages. However, only "Windows 8" is listed on the Hotfix Request page. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 8" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.
  • The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:
    VersionProductMilestoneService branch
    6.2.920 0.20 xxxWindows 8 and Windows Server 2012RTMLDR
  • The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows 8 and Windows Server 2012" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.
For all supported x86-based versions of Windows 8
File propertyValue
File nameSchannel.dll
File version6.2.9200.20810
File size325,632
Date (UTC)29-Aug-2013
Time (UTC)04:11
For all supported x64-based versions of Windows 8 and of Windows Server 2012
File propertyValue
File nameSchannel.dll
File version6.2.9200.20810
File size416,256
Date (UTC)29-Aug-2013
Time (UTC)05:25
File nameSchannel.dll
File version6.2.9200.20810
File size325,632
Date (UTC)29-Aug-2013
Time (UTC)04:11

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
More information
The maximum size of a TLS packet that travels over the network is 16 KB. In the issue that is described in this article, the server builds a list of distinguished names of the acceptable certificate authorities, and then sends the list to the client. If the number of the acceptable certificates is large (for example, more than 300 certificates), the size of the TLS packet may exceed the 16 KB limit. Therefore, the server truncates the list to 16 KB for sending the list to client.

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional file information

Additional file information for Windows 8 and Windows Server 2012

Additional files for all supported x86-based versions of Windows 8
File propertyValue
File nameX86_microsoft-windows-security-schannel_31bf3856ad364e35_6.2.9200.20810_none_1f92a99e3f9206f5.manifest
File versionNot applicable
File size13,286
Date (UTC)29-Aug-2013
Time (UTC)05:00
PlatformNot applicable
Additional files for all supported x64-based versions of Windows 8 and of Windows Server 2012
File propertyValue
File nameAmd64_microsoft-windows-security-schannel_31bf3856ad364e35_6.2.9200.20810_none_7bb14521f7ef782b.manifest
File versionNot applicable
File size13,290
Date (UTC)29-Aug-2013
Time (UTC)06:43
PlatformNot applicable
File nameWow64_microsoft-windows-security-schannel_31bf3856ad364e35_6.2.9200.20810_none_8605ef742c503a26.manifest
File versionNot applicable
File size7,312
Date (UTC)29-Aug-2013
Time (UTC)04:51
PlatformNot applicable

Article ID: 2880390 - Last Review: 10/21/2013 02:52:00 - Revision: 2.0

Windows 8, Windows 8 Enterprise, Windows 8 Pro, Windows Server 2012 Datacenter, Windows Server 2012 Essentials, Windows Server 2012 Foundation, Windows Server 2012 Standard

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