ADV170021

Описание

Microsoft has released an update for Microsoft Office that provides enhanced security as a defense-in-depth measure. The update disables the Dynamic Data Exchange protocol (DDE) in all supported editions of Microsoft Word.

Microsoft is continuing to investigate this issue and will update this advisory as further updates become available. If you are unable to install the update, or if you need to disable the DDE protocol in other Office applications, see Microsoft Security Advisory 4053440. Note that the mitigations listed in the advisory will not disable DDE, but will disable auto-update for any linked fields, including DDE.

If you need to change DDE functionality in Word after installing the update, follow these steps:

1. In the Registry Editor navigate to \HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Word\Security
   AllowDDE(DWORD)
2. Set the DWORD value based on your requirements as follows:

• AllowDDE(DWORD) = 0: To disable DDE. This is the default setting after you install the update.
• AllowDDE(DWORD) = 1: To allow DDE requests to an already running program, but prevent DDE requests that require another executable program to be launched.
• AllowDDE(DWORD) = 2: To fully allow DDE requests.

Update: On 1/9/2018, Microsoft released an update for Microsoft Office that adds defense-in-depth configuration options to selectively disable the DDE protocol in all supported editions of Microsoft Excel.

If you need to change DDE functionality in Excel after installing the update, follow these steps:

1. In the Registry Editor navigate to \HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Excel\Security DisableDDEServerLaunch(DWORD)
2. Set the DWORD value based on your requirements as follows:

• DisableDDEServerLaunch = 0: Keep DDE server launch settings unchanged from their initial behavior. This is the default setting after you install the update.
• DisableDDEServerLaunch = 1: Do not display the dialog that allows users to choose whether to launch a specific DDE server. Instead, behave automatically as though the user chose the default choice of NO.

3. In the Registry Editor navigate to \HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Excel\Security DisableDDEServerLookup(DWORD)
4. Set the DWORD value based on your requirements as follows:

• DisableDDEServerLookup = 0: Keep DDE server lookup settings unchanged from their initial behavior. This is the default setting after you install the update.
• DisableDDEServerLookup = 1: Disable querying for DDE Server availability – no query attempt will be made to find DDE servers.

Update: On 8/13/2019 Excel for Office 365 clients (>= 1902) disable DDE Server Launch by default, protecting customers out of the box from attacks targeting DDE, even if this defense-in-depth update has not been applied.

In addition to registry entries that can be configured to control DDE, Office 365 Excel clients now support:

1. Two new user controls in Trust Center to configure DDE in Excel. This can help users easily configure DDE behavior without needing to update registry.
2. Two new Group Policy controls to configure DDE in Excel. This can help enterprise administrators enforce granular security control on DDE behavior. Following is the policy information:

These policy controls should now be available in the latest Office policy templates published at: https://www.microsoft.com/download/details.aspx?id=49030.

They can also be configured using the Office cloud policy service.

Update: On 1/11/2022 Microsoft released an update for all supported versions of Excel that disables DDE Server Launch by default, protecting customers out of the box from attacks targeting DDE. DDE Server Launch can be enabled by setting the DisableDDEServerLaunch registry value to 0. Administrators can enable DDE Server Launch for Office 2016 and later by using the Group Policy template; administrators should be aware that users cannot disable DDE Server Launch if an administrator has enabled it via Group Policy. For more information see Microsoft Excel security enhancements in the January 2022 update.