December 3, the FBI and Department of Homeland Security (DHS) issued an alert for SamSam ransomware—also known as MSIL/SAMAS.A—after identifying certain cyber threat actors using the ransomware to target industries in the US.
SamSam Ransomware: How it Works
As explained in the DHS alert, the SamSam actors exploit Windows servers to gain persistent access to a victim’s network and infect all reachable hosts. According to earlier reports, this is done by:
- The cyber actors using the JexBoss Exploit Kit to access vulnerable JBoss applications
- The cyber actors using Remote Desktop Protocol (RDP) to gain persistent access to victims’ networks
After gaining access to a particular network—typically through brute force attacks or stolen login credentials—the SamSam actors escalate privileges for administrator rights, drop malware onto the server, and run an executable file, all without victims’ action or authorization.
Detecting RDP intrusions can be challenging because the malware enters through an approved access point. While many ransomware campaigns rely on a victim completing an action, such as opening an email or visiting a compromised website, RDP allows cyber actors to infect victims with minimal detection.
Protecting Against SamSam Ransomware
DHS and FBI recommend that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems and mitigate the risk of SamSam ransomware infection:
- Audit your network for systems that use RDP for remote communication. Disable the service if unneeded or install available patches. Users may need to work with their technology venders to confirm that patches will not affect system processes.
- Verify that all cloud-based virtual machine instances with public IPs have no open RDP ports, especially port 3389, unless there is a valid business reason to keep open RDP ports. Place any system with an open RDP port behind a firewall and require users to use a virtual private network (VPN) to access that system.
- Enable strong passwords and account lockout policies to defend against brute force attacks.
- Where possible, apply two-factor authentication.
- Regularly apply system and software updates.
- Maintain a good backup strategy.
- Enable logging and ensure that logging mechanisms capture RDP logins. Keep logs for a minimum of 90 days and review them regularly to detect intrusion attempts.
- When creating cloud-based virtual machines, adhere to the cloud provider’s best practices for remote access.
- Ensure that third parties that require RDP access follow internal policies on remote access.
- Minimize network exposure for all control system devices. Where possible, disable RDP on critical devices.
- Regulate and limit external-to-internal RDP connections. When external access to internal resources is required, use secure methods such as VPNs. Of course, VPNs are only as secure as the connected devices.
- Restrict users’ ability (permissions) to install and run unwanted software applications.
- Scan for and remove suspicious email attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
- Disable file and printer sharing services. If these services are required, use strong passwords or Active Directory authentication.