Adversaries may leverage remote services to move between assets and network segments. These services are often used to allow operators to interact with systems remotely within the network, some examples are RDP, SMB, SSH, and other similar mechanisms.   
Remote services could be used to support remote access, data transmission, authentication, name resolution, and other remote functions. Further, remote services may be necessary to allow operators and administrators to configure systems within the network from their engineering or management workstations. An adversary may use this technique to access devices which may be dual-homed  to multiple network segments, and can be used for Program Download or to execute attacks on control devices directly through Valid Accounts.
Specific remote services (RDP & VNC) may be a precursor to enable Graphical User Interface execution on devices such as HMIs or engineering workstation software.
Based on incident data, CISA and FBI assessed that Chinese state-sponsored actors also compromised various authorized remote access channels, including systems designed to transfer data and/or allow access between corporate and ICS networks. 
INCONTROLLER can use Telnet to upload payloads and execute commands on Omron PLCs.  The malware can also use HTTP-based CGI scripts (e.g., cpu.fcgi, ecat.fcgi) to gain administrative access to the device.
|C0009||Oldsmar Treatment Plant Intrusion|
Access Management technologies can help enforce authentication on critical remote service, examples include, but are not limited to, device management services (e.g., telnet, SSH), data access servers (e.g., HTTP, Historians), and HMI sessions (e.g., RDP, VNC).
Provide privileges corresponding to the restriction of a GUI session to control system operations (examples include HMI read-only vs. read-write modes). Ensure local users, such as operators and engineers, are giving prioritization over remote sessions and have the authority to regain control over a remote session if needed. Prevent remote access sessions (e.g., RDP, VNC) from taking over local sessions, especially those used for ICS control, especially HMIs.
|M0937||Filter Network Traffic||
Filter application-layer protocol messages for remote services to block any unauthorized activity.
|M0804||Human User Authentication||
All remote services should require strong authentication before providing user access.
Network allowlists can be implemented through either host-based files or system host files to specify what external connections (e.g., IP address, MAC address, port, protocol) can be made from a device.
Segment and control software movement between business and OT environments by way of one directional DMZs. Web access should be restricted from the OT environment. Engineering workstations, including transient cyber assets (TCAs) should have minimal connectivity to external networks, including Internet and email, further limit the extent to which these devices are dual-homed to multiple networks. 
Enforce strong password requirements to prevent password brute force methods for lateral movement.
|M0813||Software Process and Device Authentication||
All communication sessions to remote services should be authenticated to prevent unauthorized access.
|M0918||User Account Management||
Limit the accounts that may use remote services. Limit the permissions for accounts that are at higher risk of compromise; for example, configure SSH so users can only run specific programs.
|ID||Data Source||Data Component||Detects|
Monitor executed commands and arguments to services specifically designed to accept remote connections, such as RDP, Telnet, SSH, and VNC. The adversary may then perform these actions using Valid Accounts.
|DS0028||Logon Session||Logon Session Creation||
Monitor for user accounts logged into systems they would not normally access or abnormal access patterns, such as multiple systems over a relatively short period of time. 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. For added context on adversary procedures and background see Remote Services and applicable sub-techniques.
Monitor DLL file events, specifically creation of these files as well as the loading of DLLs into processes specifically designed to accept remote connections, such as RDP, Telnet, SSH, and VNC.
|DS0033||Network Share||Network Share Access||
Monitor interactions with network shares, such as reads or file transfers, using remote services such as Server Message Block (SMB). For added context on adversary procedures and background see Remote Services and applicable sub-techniques.
|DS0029||Network Traffic||Network Connection Creation||
Monitor for newly constructed network connections into a service specifically designed to accept remote connections, such as RDP, Telnet, SSH, and VNC. Monitor network connections involving common remote management protocols, such as ports tcp:3283 and tcp:5900, as well as ports tcp:3389 and tcp:22 for remote logins. The adversary may use Valid Accounts to enable remote logins.
|Network Traffic Flow||
Monitor network data for uncommon data flows (e.g., time of day, unusual source/destination address) that may be related to abuse of Valid Accounts to log into a service specifically designed to accept remote connections, such as RDP, Telnet, SSH, and VNC.
Monitor for newly executed processes related to services specifically designed to accept remote connections, such as RDP, Telnet, SSH, and VNC. The adversary may use Valid Accounts to login and may perform follow-on actions that spawn additional processes as the user.