Researchers recently observed a new malware campaign targeting Russian organization with specially crafted malicious Word documents. The malware campaign was linked to the North Korean Lazarus threat group also known as HIDDEN COBRA.
Researchers from Checkpoint noted that the Lazarus threat actor group’s new campaign targeting Russian entities uses Office documents in the initial infection stage and then drops the KEYMARBLE backdoor Trojan.
KEYMARBLE is used in the campaign by Lazarus group for accessing device configuration data, downloading additional files, executing commands, modifying the registry, capturing screenshots, and exfiltrating data.
Main infection chain
Checkpoint researchers observed the main infection chain which consists of three stages,
Researchers noted that initially the infection chain consisted of three stages, but later Lazarus group skipped the second stage of the infection chain and modified the malicious Word macros to directly download and execute the KEYMARBLE Backdoor instead of downloading the VBS script.
Decoy PDF document
The first stage of the infection chain uses malicious Word documents delivered as ZIP files, along with a decoy PDF document named NDA_USA.pdf which is a StarForce Technologies NDA agreement.
This makes the ZIP files look more legitimate thereby tricking potential Russian victims into opening both the files including the Word document which is embedded with the malicious macros.
The final payload in this campaign is downloaded from a compromised server in the form of a CAB file disguised as a JPEG image, which is later expanded into the KEYMARBLE backdoor. This also results in lower antivirus detection rate from five vendors to mere two vendors.
“A closer look at the compromised server shows an unconvincing website for the ‘Information Department’ of the ‘South Oil Company’. The server is located in Iraq and hosted by EarthLink Ltd. Communications&Internet Services,” researchers noted in a blog.