T1133:External Remote Services

Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services. Services such as Windows Remote Management can also be used externally.
Access to Valid Accounts to use the service is often a requirement, which could be obtained through credential pharming or by obtaining the credential from users after compromising the enterprise network. Access to remote services may be used as a redundant or persistent access mechanism during an operation.