Security Company: Microsoft Should Patch DDE Feature In Word

Microsoft has to come up with a solution to the DDE feature in Word now that cybercriminals use it . The Dynamic Data Exchange (DDE) feature of Word allows you to inject data from one document into a second document. Instead of a document, malicious code may also be linked. DDE is a legacy Inter-Process Communication (IPC) mechanism dating from 1987.

It consists of a protocol designed to exchange messages between two applications. In the case of DDE, it is further enhanced by giving access to shared memory. Microsoft Office provides an extension to allow DDE to communicate within external processes. Thus, DDE in a Word document may not only allow Excel to be invoked, but also to execute commands on the system via cmd.exe.

Security company SensePost warned Microsoft, but the software giant said it would not take any measures for the time being because DDE is considered a feature. It may be considered as a "candidate bug" in a subsequent version of Office. One possible reason for this is that users in multiple windows should be allowed to run the code called by DDE.

Security company EndGame decided to look into DDE within Word and discovered a bug in the implementation. The MSDN documentation about DDE states that the application that calls DDE must already run. However, that does not appear to be the case. Therefore, a malicious Word document via DDE can call cmd.exe and perform additional commands. According to Bill Finlayson of EndGame, Microsoft could resolve this by asking the user to start the app itself instead of doing this automatically.

Additionally, Microsoft can customize the text in the dialogs and make more security-oriented before running the requested application. Finlayson, however, refers to all attacks via macros that show that the end-user eventually clicks each window, regardless of the wording used. "The correct solution is therefore to ask the user to launch the application before they can click through the dialog, and then re-run the request." Finlayson is therefore sorry that Microsoft does not want to solve the problem, as attackers increasingly use this feature.

Attack Via Office DDE Feature Also Works In Microsoft Outlook

The Microsoft Office DDE feature currently used to attack Internet users through Word documents also works in Microsoft Outlook, so researchers have shown. The attack can be performed by sending emails and calendar invitations set up in Rich Text Format (RTF).

The Dynamic Data Exchange (DDE) feature of Microsoft Office makes it possible to inject data from, for example, an Excel document into a Word document. This will add code to one document that points to the data in the other document. Instead of a document, malicious code may also be linked. Attackers now use this feature to infect internet users through Word documents with ransomware and other malware.

The attackers send emails that have attached a Word document. As soon as the recipient opens the document, he will see several dialog boxes asking for permission to run the code that is linked. However, it is not necessary to send Word documents, so researchers have shown . Researcher Kevin Beaumont found a way to use the DDE feature in Microsoft Outlook via e-mail. In this case, users get the same notification as with Word asking for permission to execute code.

In addition to a RTF-generated email, the attack can also be performed via a calendar invitation. According to anti-virus company Sophos , the attack is easy to stop, users need to click on no-click in the first window asking for code execution. If the user clicked yes in the first window, a second dialog will appear for permission. Only when yes is clicked is the code called through DDE executed. Another option that users can apply to protect themselves is to display emails in plain text.