T1021 - Remote Services

Adversaries may use Valid Accounts to log into a service that accepts remote connections, such as telnet, SSH, and VNC. The adversary may then perform actions as the logged-on user.

In an enterprise environment, servers and workstations can be organized into domains. Domains provide centralized identity management, allowing users to login using one set of credentials across the entire network. If an adversary is able to obtain a set of valid domain credentials, they could login to many different machines using remote access protocols such as secure shell (SSH) or remote desktop protocol (RDP).(Citation: SSH Secure Shell)(Citation: TechNet Remote Desktop Services) They could also login to accessible SaaS or IaaS services, such as those that federate their identities to the domain.

Legitimate applications (such as Software Deployment Tools and other administrative programs) may utilize Remote Services to access remote hosts. For example, Apple Remote Desktop (ARD) on macOS is native software used for remote management. ARD leverages a blend of protocols, including VNC to send the screen and control buffers and SSH for secure file transfer.(Citation: Remote Management MDM macOS)(Citation: Kickstart Apple Remote Desktop commands)(Citation: Apple Remote Desktop Admin Guide 3.3) Adversaries can abuse applications such as ARD to gain remote code execution and perform lateral movement. In versions of macOS prior to 10.14, an adversary can escalate an SSH session to an ARD session which enables an adversary to accept TCC (Transparency, Consent, and Control) prompts without user interaction and gain access to data.(Citation: FireEye 2019 Apple Remote Desktop)(Citation: Lockboxx ARD 2019)(Citation: Kickstart Apple Remote Desktop commands)

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Correlate use of login activity related to remote services with unusual behavior or other malicious or suspicious activity. Adversaries will likely need to learn about an environment and the relationships between systems through Discovery techniques prior to attempting Lateral Movement.

Use of applications such as ARD may be legitimate depending on the environment and how it’s used. Other factors, such as access patterns and activity that occurs after a remote login, may indicate suspicious or malicious behavior using these applications. Monitor for user accounts logged into systems they would not normally access or access patterns to multiple systems over a relatively short period of time.

In macOS, you can review logs for “screensharingd” and “Authentication” event messages. Monitor network connections regarding remote management (ports tcp:3283 and tcp:5900) and for remote login (port tcp:22).(Citation: Lockboxx ARD 2019)(Citation: Apple Unified Log Analysis Remote Login and Screen Sharing)

Shield Active Defense

Network Monitoring

Monitor network traffic in order to detect adversary activity.

Network monitoring involves capturing network activity data, including capturing of server, firewall, and other relevant logs. A defender can then review them or send them to a centralized collection location for further analysis.

Opportunity

There is an opportunity to monitor network traffic for different protocols, anomalous traffic patterns, transfer of data, etc. to determine the presence of an adversary.

Use Case

The defender can implement network monitoring for and alert on anomalous traffic patterns, large or unexpected data transfers, and other activity that may reveal the presence of an adversary.

Procedures

Capture network logs for internet-facing devices and send those logs to a central collection location. Capture all network device (router, switches, proxy, etc.) logs on a decoy network and send those logs to a central collection location.