Cybersecurity researchers have discovered a new data thief called SYS01stealer. The malware targets employees of critical government infrastructure, manufacturing companies and other sectors.
“The threats behind this campaign target Facebook business accounts. They use Google Ads and fake Facebook profiles that advertise games, adult content, hacked software, etc. to lure victims into downloading a malicious file. The attacks aim to steal sensitive information, including login information, cookies, and business account information,” Morphisec said in a report.
Morphisec officials said the malware campaign was originally linked to a financially motivated cybercrime operation that Zscaler researchers dubbed "Ducktail." However, WithSecure, which first documented the cluster of Ducktail activity in July 2022, said the malware campaigns are different. This confusion points to how the attackers managed to confuse cybersecurity experts and evade detection.
The attack chain, according to Morphisec, begins when a victim clicks on a link from a fake Facebook profile or Google Ads ad to download a ZIP archive disguised as hacked software or adult content.
Opening a ZIP file launches a loader based on a legitimate C# application that is vulnerable to DLL Sideloading, allowing a malicious DLL to be loaded along with the application.
Some of the applications used to download the rogue DLL are Western Digital's WDSyncService.exe and Garmin's ElevatedInstaller.exe. In some cases, the downloaded unpublished DLL acts as a means to deploy Python and Rust-based intermediate executables. Regardless of the approach used, all paths lead to the delivery of an installer that delivers and runs the PHP-based SYS01stealer malware.
Infostealer is designed to collect Facebook cookies from Chromium-based web browsers, exfiltrate victim's Facebook information to a remote server, and download and run arbitrary files. The malware can also download files from an infected host to a C2 server, execute its commands, and update itself if a fresh version is available.
“DLL Sideloading is a very effective way to force Windows systems to load malicious code. When an application is loaded into memory, it downloads a malicious file instead of a legitimate one, allowing hackers to capture legitimate, trusted, and even signed applications for their malicious purposes,” Morphisec said.