Researchers have come across a document exploit generator that has been used over the past few years by several threat actors to deliver malware in cyber espionage campaigns.
The toolkit, dubbed “HOMEKit” by Palo Alto Networks, is believed to have been used to generate malicious Microsoft Word documents for various campaigns since 2013. Similar to the MNKit exploit generator, HOMEKit relies on the CVE-2012-0158 vulnerability in Office to deliver malware.
The most recent attack involving HOMEKit was observed by Palo Alto Networks in late June, when researchers found an email apparently coming from the United Nations Environment Programme (UNEP). The email carried a Word document and an Excel spreadsheet containing a global directory for residents of North Korea under UNEP.
While the Excel file turned out to be harmless, the Word document attempted to exploit CVE-2012-0158, which Microsoft patched in 2012, to deliver a new Trojan named “Cookle” by Palo Alto Networks.
Cookle is a newly discovered downloader that can collect information on the infected system, and download and execute files. In order to avoid being detected, the threat waits 20 minutes before contacting its command and control (C&C) server. Attackers can also configure the malware to change its sleep interval between C&C communications.
HOMEKit is designed to exploit a vulnerability in the TreeView ActiveX control. If the flaw is exploited successfully, a shellcode is executed and a decoy document is opened. In the meantime, a payload (.dat file) is executed on the system.
An analysis of the documents generated with HOMEKit showed that it had been leveraged to deliver various payloads used in the past years in cyber espionage campaigns, includingPlugX, which is often used by Chinese APTs, Surtr, seen in attacks targeting Tibetan organizations, and Mirage, which in 2012 was observed targeting energy, military and other organizations worldwide.
The exploit generator has also been used to deliver Tapaoux, a Trojan associated with theDarkHotel group, which in 2014 was spotted spying on business travelers in the Asia-Pacific region.
Researchers discovered many similarities between the documents that installed the DarkHotel malware and the ones that delivered Cookle. They determined that the functional shellcodes were more than 90 percent similar.
“The difference between the functional shellcode that installs Cookle and DarkHotel lies in the way a process is created to execute the payload and to open the decoy document,” Palo Alto’s Bryan Lee and Robert Falcone explained in a blog post. “While the difference between the two is very minor, it is worth discussing as it suggests the author of the Cookle shellcode intentionally modified the DarkHotel shellcode, possibly as an anti-analysis technique.”