A large-scale crypto-currency mining operation active for over 4 months is believed to have impacted around 30 million systems worldwide, Palo Alto Networks security researchers say.
The campaign, which attempts to mine the Monero cryptocurrency using the open-source XMRig utility, has affected mainly users in South-East Asia, Northern Africa, and South America. The campaign employed VBS files and URL shortening services to install the mining tool and also used XMRig proxy services on the hosts to mask the used wallets.
Telemetry data from the Bit.ly URL shortening service suggested that at least 15 million people were impacted. However, with less than half of the identified samples using Bit.ly, the researchers speculate that the actual number of affected users could be upwards of 30 million.
The campaign employed over 250 unique Microsoft Windows PE files, over half of which were downloaded from online cloud storage provider 4sync. What the researchers couldn’t establish, however, was how the file downloads were initiated.
The attackers attempted to make their files appear to have both generic names and to originate from popular looking file sharing services.
The Adf.ly URL shortening service that pays users when their links are clicked was also used in this campaign. When users clicked on these Adf.ly URLs, they were redirected and ended up downloading the crypto-currency mining malware instead.
The malware used in this campaign was meant to execute the XMRig mining software via VBS files and uses XMRig proxy services to hide the ultimate mining pool destination. It also uses Nicehash, a popular marketplace that allows users to trade hashing processing power (it supports various crypto-currencies and sellers are paid in Bitcoin).
Before October 20, 2017, the attackers behind this campaign were using the Windows built-in BITSAdmin tool to download the XMRig mining tool from a remote location. The final payload was mainly installed with the filename ‘msvc.exe’.
After October 20, 2017, the attackers started experimenting with HTTP redirection services, but continued using SFX files to download and deploy their malware. They also started supplementing mining queries with a username and making obfuscation attempts within the VBS files to avoid detection.
Starting on November 16, 2017, the attackers dropped the SFX files and adopted executables compiled in Microsoft .NET Framework. These would write a VBS file to disk and modify Run registry keys to achieve persistence.
In late December, the dropper was compiled with Borland Delphi and would place the VBS file in the victim’s startup folder to achieve persistence. The latest samples using this dropper also switched to a new IP address for XMRig communication, namely 5.23.48[.]207.
The campaign, researchers say, affected most countries around the world. Based on Bit.ly telemetry data, the attacks appear to have hit Thailand (3,545,437 victims), Vietnam (1,830,065), Egypt (1,132,863), Indonesia (988,163), Turkey (665,058), Peru (646,985), Algeria (614,870), Brazil (550,053), Philippines (406,294), and Venezuela (400,661) the most.
“Monero mining campaigns are certainly not a new development, as there have been various reported instances recently. However, it is less common to observe such a large-scale campaign go relatively unnoticed for such a long period of time. By targeting random end-users via malicious advertisements, using seemingly innocuous names for the malware files, and using both built-in Windows utilities and scripting files, the attackers are able to gain a foothold on victim systems at large scale,” Palo Alto concludes.
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