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 and VNC 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.
Access may also be gained through an exposed service that doesn’t require authentication. In containerized environments, this may include an exposed Docker API, Kubernetes API server, kubelet, or web application such as the Kubernetes dashboard.
Adversaries may also establish persistence on network by configuring a Tor hidden service on a compromised system. Adversaries may utilize the tool `ShadowLink` to facilitate the installation and configuration of the Tor hidden service. Tor hidden service is then accessible via the Tor network because `ShadowLink` sets up a .onion address on the compromised system. `ShadowLink` may be used to forward any inbound connections to RDP, allowing the adversaries to have remote access. Adversaries may get `ShadowLink` to persist on a system by masquerading it as an MS Defender application.
How it's found
Behavior-chain detection for T1133 External Remote Services across Windows, Linux, macOS, Containers: Unusual or unauthorized external remote access attempts (e.g., RDP, VPN, Citrix) → repeated failed logins followed by a successful session from uncommon geolocations or outside business hours → subsequent internal lateral movement or data exfiltration activities. Repeated SSH, VPN, or RDP gateway authentication attempts from external IPs → subsequent successful logon → remote shell or lateral movement activity (e.g., scp/sftp). Unexpected inbound or outbound VNC/SSH/Screen Sharing connections from external sources → repeated failed logins followed by success → remote interactive sessions or abnormal file transfers. Connections to exposed container services (e.g., Docker API, Kubernetes API server) from unauthorized external IPs → abnormal container creation/start → lateral activity within cluster nodes.
Standards mapping
Where this fits in a TurboPentest engagement
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Frequently asked questions
What is 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 and VNC 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. Access may also be gained through an exposed service that doesn’t require authentication. In containerized environments, this may include an exposed Docker API, Kubernetes API server, kubelet, or web application such as the Kubernetes dashboard. Adversaries may also establish persistence on network by configuring a Tor hidden service on a compromised system. Adversaries may utilize the tool `ShadowLink` to facilitate the installation and configuration of the Tor hidden service. Tor hidden service is then accessible via the Tor network because `ShadowLink` sets up a .onion address on the compromised system. `ShadowLink` may be used to forward any inbound connections to RDP, allowing the adversaries to have remote access. Adversaries may get `ShadowLink` to persist on a system by masquerading it as an MS Defender application.
Which tactics does T1133 belong to?
T1133 maps to the Initial Access, Persistence tactics.
Does TurboPentest test for External Remote Services?
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Related MITRE ATT&CK techniques
- Initial Access, Persistence, Privilege Escalation, StealthT1078: Valid Accounts
- Initial Access, Lateral MovementT1091: Replication Through Removable Media
- Initial AccessT1189: Drive-by Compromise
- Initial AccessT1190: Exploit Public-Facing Application
- Initial AccessT1195: Supply Chain Compromise
- Initial AccessT1199: Trusted Relationship
About this reference
These security references are maintained by IntegSec, an offensive-security firm whose team holds CISSP, OSCP, and OSCE certifications and has run thousands of penetration tests. Content is kept current as tools, standards, and attack techniques evolve.
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