Hackers Distributing FELIXROOT Backdoor Malware using Microsoft Office Vulnerabilities

Newly discovered malware campaign distributing powerful FELIXROOT Backdoor using Microsoft Office Vulnerabilities to compromise the victim’s windows computers.

FELIXROOT backdoor campaign initially discovered in September 2017 that distributed via malicious Ukrainian bank documents with macro that download the backdoor from C&C server.

Currently attackers distributing weaponized lure documents that contains exploits for Microsoft office vulnerabilities CVE-2017-0199 and CVE-2017-11882 .

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based on the source, the malware is distributed via Russian-language documents with Microsoft office Vulnerabilities.

How Does This FELIXROOT Backdoor Works

As we mentioned earlier there are two vulnerabilities (CVE-2017-0199 and CVE-2017-11882) exploiting and the malicious document distributed with the name “Seminar.rtf”.

Seminar.rtf contains embedded binary file that will be is dropped in %temp% which is used to drop and execute the FELIXROOT dropper.

FELIXROOT dropper compressed within dropped executable that will be create a two files, an LNK file that points to %system32%\rundll32.exe, and the FELIXROOT loader component.

Here the LNK file is responsible for execute the loader component of FELIXROOT and the backdoor component is completely encrypted using custom encryption that uses XOR with a 4-byte key.

After the successful execution in victims machine it sleeps 10 and the new thread will be created.

FELIXROOT  backdoor using HTTP and HTTPS POST protocols for command & control server communication and once it collected the data from the victims machine then the data sent over the network that is encrypted and arranged in a custom structure.

According to FireEye,  The malware queries the Windows API to get the computer name, user name, volume serial number, Windows version, processor architecture and two additional values.

Later all the stolen data is transferred to C2 servers using AES encryption using HTTP or HTTPS protocol and the AES key is completely unique.

After encryption, the cipher text to be sent over C2 is Base64 encoded. FELIXROOT backdoor contains various  commands for specific tasks and it used to sleep one minute before executing the next task.

Once it complete the execution and steal the compromised machine information, the  FELIXROOT  backdoor stops the loop execution and finally it wipe the footprints of the infected machine.

Indicators of Compromise

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