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External Remote Services

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.

Adversaries may use remote services to access and persist within a network. [1] 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 part of Redundant Access during an operation.

ID: T1133

Tactic: Persistence

Platform:  Windows

Permissions Required:  User

Data Sources:  Authentication logs

Contributors:  Daniel Oakley, Travis Smith, Tripwire

Version: 1.0

Examples

NameDescription
APT18

APT18 actors leverage legitimate credentials to log into external remote services.[2]

Dragonfly 2.0

Dragonfly 2.0 used VPNs and Outlook Web Access (OWA) to maintain access to victim networks.[3][4]

FIN5

FIN5 has used legitimate VPN, RDP, Citrix, or VNC credentials to maintain access to a victim environment.[5][6][7]

Ke3chang

Ke3chang regained access after eviction via the corporate VPN solution with a stolen VPN certificate, which they had extracted from a compromised host.[8]

OilRig

OilRig uses remote services such as VPN, Citrix, or OWA to persist in an environment.[9]

Threat Group-3390

Threat Group-3390 actors look for and use VPN profiles during an operation to access the network using external VPN services.[10]

Mitigation

Limit access to remote services through centrally managed concentrators such as VPNs and other managed remote access systems. Deny direct remote access to internal systems through uses of network proxies, gateways, and firewalls as appropriate. Disable or block services such as Windows Remote Management can be used externally. 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.

Detection

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.

References