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.[1] Access to remote services may be used as a redundant or persistent access mechanism during an operation.

ID: T1133
Sub-techniques:  No sub-techniques
Tactics: Persistence, Initial Access
Platforms: Linux, Windows
Permissions Required: User
Data Sources: Authentication logs
Contributors: Daniel Oakley; Travis Smith, Tripwire
Version: 2.1
Created: 31 May 2017
Last Modified: 19 June 2020

Procedure Examples

Name Description

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


APT41 compromised an online billing/payment service using VPN access between a third-party service provider and the targeted payment service.[3]


Chimera has used legitimate credentials to login to an external VPN.[4]

Dragonfly 2.0

Dragonfly 2.0 used VPNs and Outlook Web Access (OWA) to maintain access to victim networks.[5][6]


FIN5 has used legitimate VPN, Citrix, or VNC credentials to maintain access to a victim environment.[7][8][9]


GOLD SOUTHFIELD has used publicly-accessible RDP and remote management and monitoring (RMM) servers to gain access to victim machines.[10]


Ke3chang regained access after eviction via the corporate VPN solution with a stolen VPN certificate, which they had extracted from a compromised host.[11]

Linux Rabbit

Linux Rabbit attempts to gain access to the server via SSH.[12]

Night Dragon

Night Dragon has used compromised VPN accounts to gain access to victim systems.[13]


OilRig uses remote services such as VPN, Citrix, or OWA to persist in an environment.[14]

Sandworm Team

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.[15][16]

Soft Cell

Soft Cell established VPN access into victim environments.[17]


TEMP.Veles has used a VPN to persist in the victim environment.[18]

Threat Group-3390

Threat Group-3390 actors look for and use VPN profiles during an operation to access the network using external VPN services.[19] 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.[20]

Wizard Spider

Wizard Spider has accessed victim networks by using stolen credentials to access the corporate VPN infrastructure.[21]


Mitigation Description
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.

Multi-factor Authentication

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.

Network Segmentation

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.


  1. Adair, S. (2015, October 7). Virtual Private Keylogging: Cisco Web VPNs Leveraged for Access and Persistence. Retrieved March 20, 2017.
  2. Adair, S. (2017, February 17). Detecting and Responding to Advanced Threats within Exchange Environments. Retrieved March 20, 2017.
  3. Fraser, N., et al. (2019, August 7). Double DragonAPT41, a dual espionage and cyber crime operation APT41. Retrieved September 23, 2019.
  4. Cycraft. (2020, April 15). APT Group Chimera - APT Operation Skeleton key Targets Taiwan Semiconductor Vendors. Retrieved August 24, 2020.
  5. US-CERT. (2018, March 16). Alert (TA18-074A): Russian Government Cyber Activity Targeting Energy and Other Critical Infrastructure Sectors. Retrieved June 6, 2018.
  6. US-CERT. (2017, October 20). Alert (TA17-293A): Advanced Persistent Threat Activity Targeting Energy and Other Critical Infrastructure Sectors. Retrieved November 2, 2017.
  7. Scavella, T. and Rifki, A. (2017, July 20). Are you Ready to Respond? (Webinar). Retrieved October 4, 2017.
  8. Higgins, K. (2015, October 13). Prolific Cybercrime Gang Favors Legit Login Credentials. Retrieved October 4, 2017.
  9. Bromiley, M. and Lewis, P. (2016, October 7). Attacking the Hospitality and Gaming Industries: Tracking an Attacker Around the World in 7 Years. Retrieved October 6, 2017.
  10. Counter Threat Unit Research Team. (2019, September 24). REvil/Sodinokibi Ransomware. Retrieved August 4, 2020.
  11. Smallridge, R. (2018, March 10). APT15 is alive and strong: An analysis of RoyalCli and RoyalDNS. Retrieved April 4, 2018.