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.
Traffic Light Protocol
|Color||When Should it Be used?||How may it be shared?|
TLP: REDNot for disclosure, restricted to participants only.
|Sources may use TLP:RED when information cannot be effectively acted upon by additional parties, and could lead to impacts on a party's privacy, reputation, or operations if misused.||Recipients may not share TLP:RED information with any parties outside of the specific exchange, meeting, or conversation in which it was originally disclosed. In the context of a meeting, for example, TLP:RED information is limited to those present at the meeting. In most circumstances, TLP:RED should be exchanged verbally or in person.|
TLP: AMBERLimited disclosure, restricted to participants’ organizations.
|Sources may use TLP:AMBER when information requires support to be effectively acted upon, yet carries risks to privacy, reputation, or operations if shared outside of the organizations involved.||Recipients may only share TLP:AMBER information with members of their own organization, and with clients or customers who need to know the information to protect themselves or prevent further harm. Sources are at liberty to specify additional intended limits of the sharing: these must be adhered to.|
TLP: GREENLimited disclosure, restricted to the community.
|Sources may use TLP:GREEN when information is useful for the awareness of all participating organizations as well as with peers within the broader community or sector.||Recipients may share TLP:GREEN information with peers and partner organizations within their sector or community, but not via publicly accessible channels. Information in this category can be circulated widely within a particular community. TLP:GREEN information may not be released outside of the community.|
TLP: WHITEDisclosure is not limited.
|Sources may use TLP:WHITE when information carries minimal or no foreseeable risk of misuse, in accordance with applicable rules and procedures for public release.||Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction.|