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External Remote Services

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External Remote Services
ID T0822
Tactic Initial Access
Data Sources Application Log: Application Log Content, Logon Session: Logon Session Metadata, Network Traffic: Network Traffic Flow
Asset Control Server, Input/Output Server


Adversaries may leverage external remote services as a point of initial access into your network. These services allow users to connect to internal network resources from external locations. Examples are VPNs, Citrix, and other access mechanisms. Remote service gateways often manage connections and credential authentication for these services.1

External remote services allow administration of a control system from outside the system. Often, vendors and internal engineering groups have access to external remote services to control system networks via the corporate network. In some cases, this access is enabled directly from the internet. While remote access enables ease of maintenance when a control system is in a remote area, compromise of remote access solutions is a liability. The adversary may use these services to gain access to and execute attacks against a control system network. Access to valid accounts is often a requirement.

As they look for an entry point into the control system network, adversaries may begin searching for existing point‐to‐point VPN implementations at trusted third party networks or through remote support employee connections where split tunneling is enabled.2

In the Maroochy Attack, the adversary was able to gain remote computer access to the system over radio.

Procedure Examples

  • In the Ukraine 2015 Incident, Sandworm Team harvested VPN worker credentials and used them to remotely log into control system networks.2345


  • Disable or Remove Feature or Program - Consider removal of remote services which are not regularly in use, or only enabling them when required (e.g., vendor remote access). Ensure all external remote access point (e.g., jump boxes, VPN concentrator) are configured with least functionality, especially the removal of unnecessary services.6
  • Multi-factor Authentication - Use strong multi-factor authentication for remote service accounts to mitigate an adversary's ability to leverage stolen credentials. Be aware of multi-factor authentication interception techniques for some implementations.
  • Network Segmentation - Deny direct remote access to internal systems through the use of network proxies, gateways, and firewalls. Consider a jump server or host into the DMZ for greater access control. Leverage this DMZ or corporate resources for vendor access.7
  • User Account Management - Consider utilizing jump boxes for external remote access. Additionally, dynamic account management may be used to easily remove accounts when not in use.
  • Account Use Policies - Configure features related to account use like login attempt lockouts, specific login times, and password strength requirements as examples. Consider these features as they relate to assets which may impact safety and availability.7