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. In the Oldsmar water treatment attack, adversaries gained access to the system through remote access software, allowing for the use of the standard operator HMI interface.  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. 
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|
|DS0028||Logon Session||Logon Session Creation|
|DS0033||Network Share||Network Share Access|
|DS0029||Network Traffic||Network Connection Creation|
|Network Traffic Content|
|Network Traffic Flow|