Threat Signal Report
BlackMatter Uses New Custom Data Exfiltration Tool
FortiGuard Labs is aware that a BlackMatter ransomware affiliate started to use a new custom data exfiltration tool called "Exmatter". The tool is used to steal specific file types from predetermined directories and upload them to an attacker's server. This process happens before the ransomware is deployed to the victim's network.
Why is this Significant?
This is significant because Exmatter appears to target specific file types which the attacker thinks are valuable so it can steal them as quickly as possible. That allows the attacker to spend less time on the network before deploying the BlackMatter ransomware.
What File Types is Exmatter Designed to Steal?
According to security vendor Symantec, files with the following file extensions on the compromised machine are targeted by Exmatter:
Are There Multiple Versions of Exmatter?
According to the security vendor, there are at least four versions of Exmatter that were used by a BlackMatter affiliate. Newer versions include additional file extensions to steal, as well as specific strings in file names that Exmatter excludes from the exfiltration targets. One directory target was shortened so that Exmatter can search for more files for exfiltration. Also SFTP server details used for uploading the stolen data were updated with Webdav to serve as a backup in case the SFTP transmission did not work.
What is the Significance of the Updates Made to Exmatter?
It is significant because the attacker used lessons learned from the networks of previous victims to update Exmatter to make data exfiltration more efficient and effective against future victims.
What does FortiGuard Labs Know About BlackMatter Ransomware?
BlackMatter ransomware is a fairly new Ransomware-as-a-Service (RaaS) and was discovered in late July 2021. The group posted ads on hacking forums recruiting affiliates and asking to buy access to compromised corporate networks to deploy ransomware. FortiGuard Labs has previously released two Threat Signals on BlackMatter ransomware. See the Appendix for a link to the Threat Signal, "Meet BlackMatter: Yet Another RaaS in the Wild" and to the Threat Signal, "Joint CyberSecurity Advisory on BlackMatter Ransomware (AA21-291A)."
What is the Status of Coverage?
FortiGuard Labs provides the following AV coverage against Exmatter:
All Network IOC's related to this threat are blocked by the FortiGuard WebFiltering Client.