The FELIXROOT backdoor was first spotted by FireEye in September 2017, when attackers used it in attacks targeting Ukrainians.

The new spam campaign used weaponized documents claiming to provide information on a seminar on environmental protection efforts.

The documents include code to exploit known Microsoft Office vulnerabilities CVE-2017-0199 and CVE-2017-11882 to drop and execute the backdoor binary.

Experts reported that the lure documents used in the last campaign were written in the Russian language. The weaponized document exploits the CVE-2017-0199 flaw to download a second-stage payload that triggers the CVE-2017-11882 vulnerability to drop and execute the final backdoor.

“FireEye recently observed the same FELIXROOT backdoor being distributed as part of a newer campaign. This time, weaponized lure documents claiming to contain seminar information on environmental protection were observed exploiting known Microsoft Office vulnerabilities CVE-2017-0199 and CVE-2017-11882 to drop and execute the backdoor binary on the victim’s machine.” reads the analysis published by FireEye.

“After successful exploitation, the dropper component executes and drops the loader component. The loader component is executed via RUNDLL32.EXE. The backdoor component is loaded in memory and has a single exported function,”

The CVE-2017-0199 allows the attackers to download and execute a Visual Basic script containing PowerShell commands when the victim opens the lure document.

The CVE-2017-11882 is remote code execution vulnerability that allows the attacker to run arbitrary code in the context of the current user.