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.[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.[2] 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.[3][4]

ID: T1133
Sub-techniques:  No sub-techniques
Platforms: Containers, Linux, Windows, macOS
Contributors: Alfredo Oliveira, Trend Micro; Ariel Shuper, Cisco; Brad Geesaman, @bradgeesaman; Daniel Oakley; David Fiser, @anu4is, Trend Micro; David Tayouri; ExtraHop; Idan Frimark, Cisco; Jay Chen, Palo Alto Networks; Magno Logan, @magnologan, Trend Micro; Rory McCune, Aqua Security; Travis Smith, Tripwire; Vishwas Manral, McAfee; Yossi Weizman, Azure Defender Research Team; Yuval Avrahami, Palo Alto Networks
Version: 2.4
Created: 31 May 2017
Last Modified: 30 March 2023

Procedure Examples

ID Name Description
C0028 2015 Ukraine Electric Power Attack

During the 2015 Ukraine Electric Power Attack, Sandworm Team installed a modified Dropbear SSH client as the backdoor to target systems. [5]

G0026 APT18

APT18 actors leverage legitimate credentials to log into external remote services.[6]

G0007 APT28

APT28 has used Tor and a variety of commercial VPN services to route brute force authentication attempts.[7]

G0016 APT29

APT29 has used compromised identities to access networks via VPNs and Citrix.[8][9]

G0096 APT41

APT41 compromised an online billing/payment service using VPN access between a third-party service provider and the targeted payment service.[10]

C0027 C0027

During C0027, Scattered Spider used Citrix and VPNs to persist in compromised environments.[11]

G0114 Chimera

Chimera has used legitimate credentials to login to an external VPN, Citrix, SSH, and other remote services.[12][13]

C0004 CostaRicto

During CostaRicto, the threat actors set up remote tunneling using an SSH tool to maintain access to a compromised environment.[14]

S0600 Doki

Doki was executed through an open Docker daemon API port.[15]

G0035 Dragonfly

Dragonfly has used VPNs and Outlook Web Access (OWA) to maintain access to victim networks.[16][17]

G1016 FIN13

FIN13 has gained access to compromised environments via remote access services such as the corporate virtual private network (VPN).[18]

G0053 FIN5

FIN5 has used legitimate VPN, Citrix, or VNC credentials to maintain access to a victim environment.[19][20][21]


GALLIUM has used VPN services, including SoftEther VPN, to access and maintain persistence in victim environments.[22][23]


GOLD SOUTHFIELD has used publicly-accessible RDP and remote management and monitoring (RMM) servers to gain access to victim machines.[24]

S0601 Hildegard

Hildegard was executed through an unsecure kubelet that allowed anonymous access to the victim environment.[4]

G0004 Ke3chang

Ke3chang has gained access through VPNs including with compromised accounts and stolen VPN certificates.[25][26]

G0094 Kimsuky

Kimsuky has used RDP to establish persistence.[27]

S0599 Kinsing

Kinsing was executed in an Ubuntu container deployed via an open Docker daemon API.[28]


LAPSUS$ has gained access to internet-facing systems and applications, including virtual private network (VPN), remote desktop protocol (RDP), and virtual desktop infrastructure (VDI) including Citrix. [29][30]

G0065 Leviathan

Leviathan has used external remote services such as virtual private networks (VPN) to gain initial access.[31]

S0362 Linux Rabbit

Linux Rabbit attempts to gain access to the server via SSH.[32]

S1060 Mafalda

Mafalda can establish an SSH connection from a compromised host to a server.[33]

C0002 Night Dragon

During Night Dragon, threat actors used compromised VPN accounts to gain access to victim systems.[34]

G0049 OilRig

OilRig uses remote services such as VPN, Citrix, or OWA to persist in an environment.[35]

C0012 Operation CuckooBees

During Operation CuckooBees, the threat actors enabled WinRM over HTTP/HTTPS as a backup persistence mechanism using the following command: cscript //nologo "C:\Windows\System32\winrm.vbs" set winrm/config/service@{EnableCompatibilityHttpsListener="true"}.[36]

C0014 Operation Wocao

During Operation Wocao, threat actors used stolen credentials to connect to the victim's network via VPN.[37]

G0034 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.[38][39][40]

G1015 Scattered Spider

Scattered Spider has leveraged legitimate remote management tools to maintain persistent access.[41]

C0024 SolarWinds Compromise

For the SolarWinds Compromise, APT29 used compromised identities to access networks via SSH, VPNs, and other remote access tools.[42][43]

G0139 TeamTNT

TeamTNT has used open-source tools such as Weave Scope to target exposed Docker API ports and gain initial access to victim environments.[44][45] TeamTNT has also targeted exposed kubelets for Kubernetes environments.[4]

G0088 TEMP.Veles

TEMP.Veles has used a VPN to persist in the victim environment.[46]

G0027 Threat Group-3390

Threat Group-3390 actors look for and use VPN profiles during an operation to access the network using external VPN services.[47] 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.[48]

G0102 Wizard Spider

Wizard Spider has accessed victim networks by using stolen credentials to access the corporate VPN infrastructure.[49]


ID Mitigation Description
M1042 Disable or Remove Feature or Program

Disable or block remotely available services that may be unnecessary.

M1035 Limit Access to Resource Over Network

Limit access to remote services through centrally managed concentrators such as VPNs and other managed remote access systems.

M1032 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 Multi-Factor Authentication Interception techniques for some two-factor authentication implementations.

M1030 Network Segmentation

Deny direct remote access to internal systems through the use of network proxies, gateways, and firewalls.


ID Data Source Data Component Detects
DS0015 Application Log Application Log Content

When authentication is not required to access an exposed remote service, monitor for follow-on activities such as anomalous external use of the exposed API or application.

DS0028 Logon Session Logon Session Metadata

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.

DS0029 Network Traffic Network Connection Creation

Monitor for newly constructed network connections that may use Valid Accounts to access and/or persist within a network using External Remote Services. Use of External Remote Services may be legitimate depending on the environment and how it’s used. Other factors, such as access patterns and activity that occurs after a remote login, may indicate suspicious or malicious behavior using External Remote Services.

Network Traffic Content

Monitor and analyze traffic patterns and packet inspection associated to protocol(s) that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).

Network Traffic Flow

Monitor for network traffic originating from unknown/unexpected hardware devices. Local network traffic metadata (such as source MAC addressing) as well as usage of network management protocols such as DHCP may be helpful in identifying hardware.


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