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Issues with SYSVOL share after installing KB3161561

Recently, I got funny issues with group policies on Windows Server 2012 R2. These issues manifested themselves with the following symptoms:

  • When trying to edit a group policy, the Group Policy Management tool would present an error like “Group Policy Error: You do not have permission to perfrom this operation. Details: Access is denied.” The Group Policy Management Editor would still open, but the group policy would not be displayed.
  • Sometimes, the group policy editor would open, but when trying to navigate through the tree, it would display an error message like “Error (0x80070005) occurred parsing file. Access is denied.”  I believe that this error is only present when using the central store for administrative templates.
  • The event log would contain messages like: “The processing of Group Policy failed. Windows attempted to read the file \\domain\sysvol\domain\Policies\uuid\gpt.ini from a domain controller and was not successful. Group Policy settings may not be applied until this event is resolved. This issue may be transient and could be caused by one or more of the following:
    a) Name Resolution/Network Connectivity to the current domain controller.
    b) File Replication Service Latency (a file created on another domain controller has not replicated to the current domain controller).
    c) The Distributed File System (DFS) client has been disabled.”
  • When trying to open \\domain.example.com\SYSVOL in the file brower, a prompt to enter credentials or an “Access is denied” error message would be displayed.

Like suggested in the TechNet forums, disabling the “Hardened UNC paths” feature that was introduced with KB3000483 fixed these issues, but obviously this is not a solution because this will actually reintroduce the vulnerability (MITM-attack on SYSVOL share) that was addressed by KB3000483.

After some time, I realized that these problems had first appeared after installing the June security updates, so I looked through the corresponding knowledge base articles and found KB3161561. This article actually mentions (some of) the issues described earlier in the “Known issues in this security update” section. It also offers a different workaround that works without disabling the “Hardened UNC paths” feature: Setting the “SmbServerNameHardeningLevel” to 0. However, using this workaround has other security implications (described in an MSDN article). Last but not least, MS15-083 describes a third workaround that involves disabling version 1 of the SMB protocol on the server, but this workaround did not solve the problem for me.

Changing the “SmbServerNameHardeningLevel” to 0 might not work when this setting is reset by a group policy (as it was in my case). In this case, the corresponding group policy needs to be changed and the “Computer Configuration\Windows Settings\Local Policies\Security Options\Microsoft network server: Server SPN target name validation level” option needs to be set to “Off”.

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