When combining exploits for added effect goes wrong

Since public disclosure in April 2017, CVE-2017-0199 has been frequently used within malicious Office documents. The vulnerability allows attackers to include Ole2Link objects within RTF documents to launch remote code when HTA applications are opened and parsed by Microsoft Word.

In this recent campaign, attackers combined CVE-2017-0199 exploitation with an earlier exploit, CVE-2012-0158, possibly in an attempt to evade user prompts by Word, or to arrive at code execution via a different mechanism. Potentially, this was just a test run in order to test a new concept. In any case, the attackers made mistakes which caused the attack to be a lot less effective than it could have been.

Analysis of the payload highlights the potential for the Ole2Link exploit to launch other document types, and also demonstrates a lack of rigorous testing procedures by at least one threat actor.

Attackers are obviously trying to find a way around known warning mechanisms alerting users about potential security issues with opened documents. In this blog post we analyse what happens when an attack attempts to combine these two exploits in a single infection chain and fails.

Although this attack was unsuccessful it has shown a level of experimentation by attackers seeking to use CVE-2017-0199 as a means to launch additional weaponized file types and avoid user prompts. It may have been an experiment that didn’t quite work out, or it may be indication of future attacks yet to materialise.