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 credentials from users after compromising the enterprise network. Access to remote services may be used as a redundant or persistent access mechanism during an operation.
Sandworm Team has used Dropbear SSH with a hardcoded backdoor password to maintain persistence within the target network. Sandworm Team has also used VPN tunnels established in legitimate software company infrastructure to gain access to internal networks of that software company's users.
Threat Group-3390 actors look for and use VPN profiles during an operation to access the network using external VPN services. Threat Group-3390 has also obtained OWA account credentials during intrusions that it subsequently used to attempt to regain access when evicted from a victim network.
|Disable or Remove Feature or Program||
Disable or block remotely available services that may be unnecessary.
|Limit Access to Resource Over Network||
Limit access to remote services through centrally managed concentrators such as VPNs and other managed remote access systems.
Use strong two-factor or multi-factor authentication for remote service accounts to mitigate an adversary's ability to leverage stolen credentials, but be aware of Two-Factor Authentication Interception techniques for some two-factor authentication implementations.
Deny direct remote access to internal systems through the use of network proxies, gateways, and firewalls.
Follow best practices for detecting adversary use of Valid Accounts for authenticating to remote services. Collect authentication logs and analyze for unusual access patterns, windows of activity, and access outside of normal business hours.
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