Researchers discover threat actors with links to SolarWinds hack

Report shines a light on the overlap between SilverFish cybercrime group victims and SolarWinds targets

A group of hackers behind the Russian flag

Security researchers have discovered a large cyber spying group with links to the recent SolarWinds attacks.

According to a report from cyber security firm Prodaft, the 'Silverfish' hacking group carried out numerous attacks since August, including stealing confidential data from government agencies and other organizations.

Researchers gained the information by infiltrating the hackers’ command and control (C2) servers. This revealed Silverfish had targeted at least 4,720 victims over the past few months, and researchers said there was a significant overlap with the companies affected by the SolarWinds attacks.

The victims included governmental institutions, global IT providers, the aviation industry, and defense companies. Following the disclosure of the SolarWinds attack in December, a client in the financial sector who’d been breached in the attacks called the researchers.

Based on public indicators of compromise published by FireEye, the researchers created a unique fingerprint of one of the online servers. The team then searched all IPv4 ranges globally to find a matching fingerprint, resulting in positive detections within 12 hours of the scan. 

Once the team gained access to a C2 server, they found SilverFish had four teams actively exploiting the victims’ devices. SilverFish uses a team-based workflow model and a triage system similar to modern project management applications like Jira.

“Whenever a new victim is infected, it is assigned to the current ‘Active Team’ which is pre-selected by the administrator. Each team on the C&C server can only see the victims assigned to them. Furthermore, the system has the capability to auto-assign victims based on the current workload,” said researchers.

Researchers said while the US is by far the most frequently targeted region with 2,465 attacks recorded, 1,645 victims were from several European countries.

While the hackers mainly used English, there were comments written in Russian slang and vernacular. Evidence researchers found suggested the hackers ran servers in Ukraine and Russia.

Most of the group’s work occurred between 08:00 and 20:00 (UTC).

“From our point of view, this illustrates the existence of an organization that operates in an organized and disciplined manner in a hierarchical environment, one that is even highly compartmentalized,” said researchers.

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