Microsoft Office Defense in Depth Update

ADV170021
Security Advisory

Released: Dec 12, 2017

Last updated: Jan 11, 2022

Assigning CNA
Microsoft

Executive Summary

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.
  1. In the Registry Editor navigate to \HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Excel\Security DisableDDEServerLookup(DWORD)
  2. 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:
Policy path Setting Name
User\Microsoft Excel 2016\Excel Options\Security\Trust Center\External Content\ Don't allow Dynamic Data Exchange (DDE) server launch in Excel
User\Microsoft Excel 2016\Excel Options\Security\Trust Center\External Content\ Don't allow Dynamic Data Exchange (DDE) server lookup in Excel

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.

Exploitability

The following table provides an exploitability assessment for this vulnerability at the time of original publication.

Publicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation More Likely

FAQ

I have Microsoft Word 2010 installed. Why am I not being offered the 4011612 update? The 4011612 update only applies to systems running specific configurations of Microsoft Office 2010. Some configurations will not be offered the update.

I am being offered this update for software that is not specifically indicated as being affected in the Affected Software and Vulnerability Severity Ratings table. Why am I being offered this update? When updates address vulnerable code that exists in a component that is shared between multiple Microsoft Office products or shared between multiple versions of the same Microsoft Office product, the update is considered to be applicable to all supported products and versions that contain the vulnerable component.

For example, when an update applies to Microsoft Office 2007 products, only Microsoft Office 2007 may be specifically listed in the Affected Software table. However, the update could apply to Microsoft Word 2007, Microsoft Excel 2007, Microsoft Visio 2007, Microsoft Compatibility Pack, Microsoft Excel Viewer, or any other Microsoft Office 2007 product that is not specifically listed in the Affected Software table. Furthermore, when an update applies to Microsoft Office 2010 products, only Microsoft Office 2010 may be specifically listed in the Affected Software table. However, the update could apply to Microsoft Word 2010, Microsoft Excel 2010, Microsoft Visio 2010, Microsoft Visio Viewer, or any other Microsoft Office 2010 product that is not specifically listed in the Affected Software table.

For more information on this behavior and recommended actions, see Microsoft Knowledge Base Article 830335. For a list of Microsoft Office products that an update may apply to, refer to the Microsoft Knowledge Base Article associated with the specific update.

Acknowledgements

  • CERT-IL
  • Saif El-Sherei, and Etienne Stalmans
Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgements for more information.

Security Updates

To determine the support lifecycle for your software, see the Microsoft Support Lifecycle.

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Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

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