Google announced last month that the Lazarus-sponsored state-based North Korean hacking community carried out attacks on security scholars in social engineers, wherein the hacking community used social networks as a tool to target security researchers and used custom backdoor malware. The Lazarus group is a North Korea based persistent threat group (APT), which has gained a lot of prominence in the preceding years as various CyberAttacks have been attributed to the threat group.
The threat actors have developed comprehensive online "security researcher" personas who then use social media to connect with renowned security researchers to contribute to the vulnerability and exploit growth to execute their attacks.
In this regard, the attackers have sent malignant Visual Studio Projects and links to the website that hosts the exploit kits to install backdoors in the computers of the researchers. Microsoft also announced that it had monitored the assault and saw Lazarus exchanging MHTML files containing malicious java scripts with the researchers. The server command and control at the time of the investigation was down and therefore no further payloads were investigated by Microsoft.
Recently in this social-engineering campaign, South Korean cybersecurity company ENKI claimed that Lazarus attacked MHTML files on their squad. Although the attacks were ineffective, they analyzed payloads downloaded from MHT files and found that they contained a vulnerability exploit for Internet Explorer.
MHT/MHTML is a file format that is used by Internet Explorer to store a web page and services in one file. MHT / MHTML file is sometimes also known as MIME HTML. The MHT file transmitted to ENKI investigators was confirmed to be an exploit of Chrome 85 RCE and called "Chrome_85_RCE_Full_Exploit_Code.mht."
On further executing the MHT/MHTML file, Internet Explorer will automatically start to display the MHT file contents. ENKI stated that a malicious javascript would download two payloads with one containing a zero-day version of Internet Explorer if the execution of the script was allowed. ENKI has affirmed that they have reported the bug to Microsoft and for which they were later contacted by a Microsoft employee.
Concerning the aforementioned incident, Microsoft has said that they have investigated every aspect of the report and will surely provide an update in near future, “Microsoft has a customer commitment to investigate reported security issues and we will provide updates for impacted devices as soon as possible.”