Microsoft Security Advisory (935964) - Check your DNS

Disable remote management over RPC capability for DNS Servers through the registry key setting.

Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in regedit.exe.

Note We recommend backing up the registry before you edit it.

Managed Deployment Script

The following sample registry script can be used to enable this registry setting:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS\Parameters]

"RpcProtocol"=dword:00000004

The above registry script can be saved to a file with a .REG file extension and can be deployed silently as part of an automated deployment script using regedit.exe using the /s command line switch.

The DNS service needs to be restarted for this change to take effect.

For help using regedit.exe to deploy registry scripts please refer to Microsoft Knowledge Base Article Q82821: Registration Info Editor (REGEDIT) Command-Line Switches.

How to undo workaround: To undo the workaround perform the following steps:

RpcProtocol registry key values

The value ‘4’ being used above restricts the DNS RPC interface to LPC-only.  Combine values from the table below to change the transport mechanisms allowed set to the RpcProtocol key. 

You can re-configure the DNS server’s management interface to accept only LPC by setting a value in the registry Other registry values will modify or disable RPC communication differently. For more information on the RpcProtocol registry key please see the following TechNet article. Setting the value to 4 will mitigate a remote attempt to exploit the vulnerability. Setting the value to 0 will disable all DNS RPC functionality and will protect against both local and remote attempts to exploit the vulnerability.

Impact of Workaround: Setting the registry value to 4 will disable remote management and configuration of DNS server functionality using RPC or WMI will be disabled. DNS management tools, will fail to work remotely. Local management and remote management through terminal services can be still used to manage your DNS Server configuration.

You will still be able to use the DNS management MMC Snap-in, DNSCMD.exe, and the DNS WMI provider.

Setting the registry value to 0 will disable all DNS RPC management capability including local administration and configuration

DNS Server local administration and configuration may not work if the server being managed has a computer name of 15 characters or longer and is selected by its computer name. To avoid this issue, use the Fully Qualified Domain Name (FQDN) of the computer being managed in the DNS administration tools.

Block the following at the firewall:

Block TCP and UDP port 445 as well as all unsolicited inbound traffic on ports greater than 1024.

The RPC interface of Windows DNS is bound to a port greater than 1024. While the majority of RPC port binding occurs between the 1024 to 5000 range it is possible for the RPC interface to potentially bind to higher unreserved port numbers. Blocking them at the firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability. We recommend that you block all unsolicited inbound communication from the Internet to help prevent attacks that may use other ports. For more information about ports that RPC uses, visit the following Web site. To block all unsolicited RPC requests while preserving DNS management functionality please see Microsoft Knowledge Base Article 555381

Impact of Workaround: Remote management of DNS server functionality using RPC will be disabled. DNS management tools, will fail to work remotely. Local and remote management through terminal services can be still used to manage your DNS Server configuration

This includes the DNS management MMC Snap-in, DNSCMD.exe, DNS WMI provider. Additional management and control functionality may be lost for applications or components that use the affected ports.

Blocking port 445 will prevent computers connecting to the server through SMB as well as the server will being unable to access folders shared on the network. Management tools that depend on SMB for connectivity will be unable to connect to the server.

Enable advanced TCP/IP filtering on systems

You can enable advanced TCP/IP filtering to block all unsolicited inbound traffic. For more information about how to configure TCP/IP filtering, see Microsoft Knowledge Base Article 309798.

Block TCP and UDP port 445 as well as affected ports greater than 1024 by using IPsec on the affected systems

Use Internet Protocol security (IPsec) to help protect network communications. Detailed information about IPsec and about how to apply filters is available in Microsoft Knowledge Base Article 313190 and Microsoft Knowledge Base Article 813878.

Impact of Workaround: Remote management of DNS server functionality using RPC will be disabled. DNS management tools, will fail to work remotely. Local and remote management through terminal services can be still used to manage your DNS Server configuration

This includes the DNS management MMC Snap-in, DNSCMD.exe, DNS WMI provider. Additional management and control functionality may be lost for applications or components that use affected ports.

Blocking port 445 will prevent computers connecting to the server through SMB as well as the server will being unable to access folders shared on the network. Management tools that depend on SMB for connectivity will be unable to connect to the server.