Shortcuts As Entry Points For Malware Part 2

Jean-Pierre LESUEUR

It was only yesterday that we reported about a way of infecting Microsoft Windows users by using a simple shortcut trick with the BITSAdmin Tool to download and execute a remote application.

If you haven’t already read the article, please click here.

The main issue with the first example is that your firewall could potentially block the download attempt since it requires a remote http/https connection to download the file before its execution.

Our security researcher has found another sneaky way of exploiting the Windows shortcut with a new 0day by embedding any files (such as application files) directly inside the shortcut itself.

Yes! the application is inside the Windows shortcut

This makes the malicious application fully undetectable by any antivirus software before it will be dropped and executed.

Note: An an example, in the PoC mentioned below, we decided to use this vulnerability as a file dropper, but we could also create a version that injects the binary file directly into memory without being written to disk to become even more undectable for antivirus software on its execution. We will probably write another article about this method later

Shortcuts As Entry Points For Malware

Jean-Pierre LESUEUR

We came across a way of installing malware threats in a Microsoft Windows Operating System using the well-known Shortcut System that nearly everybody uses and blindly trusts.

Because of it's very nature, it is quite hard to detect. Removal might even be more difficult.

Preface


  • A shortcut isn’t a binary executable file. At least not directly, as it mostly points to another location folder or file. However, it can also execute Windows shell commands (which is potentially a very dangerous feature, but often used for programming tasks such as system shutdown/logoff/restart directly via a regular shortcut).
  • Since a shortcut isn’t a binary executable, an antivirus program will not detect such a shortcut as a possible malicious shortcut.
  • Shortcuts can be shared through archive files without losing its properties.
  • Finally you can easily change the icon and disguise the malicious shortcut with a folder icon or an image. This could help spreading the malware via social media.

Description


To describe this threat, we shall first describe a native Windows program, called BITSAdmin Tool and which is embedded in Windows since Windows XP SP2. Follow this MSDN link for more information about how to use it and what it is used for.