In the recent weeks we are more and more often reading news that talks about attacks that exploit DDE technology, Botnets that exploit the DDE attack, Ransomware that are distributed via DDE attack and so on.
Well, this is the right time to clarify this technology and this new attack way.
Let's start from the basics, what is DDE?
DDE, which stands for Dynamic Data Exchange, it is an interprocess communication system (IPC) introduced for the first time in 1987 with Windows 2.0.
This technology and its functionality have been largely supplanted by OLE - Object Linking and Embedding. However, DDE is still used due to its simplicity.
Like macros, DDE is a legitimate feature of Microsoft Office and allows to share a set of data between applications. For example, you could create a Word document linked to an Excel document so that the data in the first one will be updated automatically whenever are you changing Excel spreadsheet data.
In which way this attack is bring out?
Performing a DDE attack is very simple. Just add the string {DDEAUTO} to call the DDE feature, , in the text of a Microsoft Word document, followed by the command you want to run, all within the braces.
Can it be used only in Office documents?
No, not only Microsoft Office documents.
This attack can also pull off via Outlook, by sending an email, an email or an appointment, known as "calendar" in company jargon.
Now we are going to create a formatted content using Microsoft Outlook's "Rich Text Format" (RTF) and insert the malicious code inside it and save it as email. Next step will be to attach this one to the email we'd like to send, write a a title and a text to attracting victim's attention and push it to open it.
What can you do with this attack?
In which DDE attack would be used:
- to send a computer in Denial Of Service (DOS) by running countless instances of a specific software until the available resources are saturated;
- running software or scripts that could give full control of the computer to the attacker;
- download malware to use to exfiltrate data.
How to recognize fraudulent content?
When you are opening the file, a warning message is showed to you. It is warning yo that the file has an external contents and asks for confirmation to continue.
If your chiose has been "YES", a new message will be displayed asking if you want to run a specified application. The in example below the command / application quoted is "cmd.exe".
However, it should be noted that the information concerning the execution of the command can be hidden or omitted by editing the syntax of the malicious code.
How to defend yourself?
When the warning message realated external contents has popped out, clicking "No" block the attack attempted.
You can also defend yourself better by changind setting and display all messages in text format.
However, this workaround involves the deactivation of all formatting, colors and images from all incoming e-mails and consequently some contents could not be rendered.
Why this new attack?
Cyber criminals are starting to use DDE technology because it is different from macro and because they are always looking for new ways to mislead the victim.
For years we are witnessing attacks based on the macro but fortunately you can disable this technology and therefore prevent malicious content from being automatically performed when the file is opened.
This new way, though it has some limits dictated by the interaction with the user, could lead an untrained or careless person to think that it is an error that occurred due some file's errors.
In the last weeks this new attack way has grown exponentially thanks to the fact that you do not have to send attached to the email documents of Microsoft Office or PDF, but just attach another email or a "calendar".
Please note, this article was created in the end of October 2017, but only at this time I have been able to publish it.