T1021: Remote Services
Adversaries may use Valid Accounts to log into a service that accepts remote connections, such as telnet, SSH, and VNC. The adversary may then perform actions as the logged-on user.
In an enterprise environment, servers and workstations can be organized into domains. Domains provide centralized identity management, allowing users to login using one set of credentials across the entire network. If an adversary is able to obtain a set of valid domain credentials, they could login to many different machines using remote access protocols such as secure shell (SSH) or remote desktop protocol (RDP). They could also login to accessible SaaS or IaaS services, such as those that federate their identities to the domain, or management platforms for internal virtualization environments such as VMware vCenter.
Legitimate applications (such as Software Deployment Tools and other administrative programs) may utilize Remote Services to access remote hosts. For example, Apple Remote Desktop (ARD) on macOS is native software used for remote management. ARD leverages a blend of protocols, including VNC to send the screen and control buffers and SSH for secure file transfer. Adversaries can abuse applications such as ARD to gain remote code execution and perform lateral movement. In versions of macOS prior to 10.14, an adversary can escalate an SSH session to an ARD session which enables an adversary to accept TCC (Transparency, Consent, and Control) prompts without user interaction and gain access to data.
How it's found
Behavioral Detection Strategy for Remote Service Logins and Post-Access Activity: Logon via RDP or WMI by a user account followed by uncommon command execution, file manipulation, or lateral network connections. SSH session from new source IP followed by interactive shell or privilege escalation (e.g., sudo, su) and outbound lateral connection. Remote login via ARD or SSH followed by screensharingd process activity or modification of TCC-protected files. Use of cloud-based bastion or VM console session followed by commands that initiate outbound SSH or RDP sessions from the cloud instance to other environments. vSphere API logins (vimService) or SSH to ESXi host followed by unauthorized shell commands or lateral remote logins from the ESXi host.
Sub-techniques
T1021.001: Remote Desktop Protocol
Adversaries may use Valid Accounts to log into a computer using the Remote Desktop Protocol (RDP). The adversary may then perform actions as the logged-on user. Remote desktop is a common feature in operating systems. It allows a user to log into an interactive session with a system desktop graphical user interface on a remote system. Microsoft refers to its implementation of the Remote Desktop Protocol (RDP) as Remote Desktop Services (RDS). Adversaries may connect to a remote system over RDP/RDS to expand access if the service is enabled and allows access to accounts with known credentials. Adversaries will likely use Credential Access techniques to acquire credentials to use with RDP. Adversaries may also use RDP in conjunction with the Accessibility Features or Terminal Services DLL for Persistence.
T1021.002: SMB/Windows Admin Shares
Adversaries may use Valid Accounts to interact with a remote network share using Server Message Block (SMB). The adversary may then perform actions as the logged-on user. SMB is a file, printer, and serial port sharing protocol for Windows machines on the same network or domain. Adversaries may use SMB to interact with file shares, allowing them to move laterally throughout a network. Linux and macOS implementations of SMB typically use Samba. Windows systems have hidden network shares that are accessible only to administrators and provide the ability for remote file copy and other administrative functions. Example network shares include `C$`, `ADMIN$`, and `IPC$`. Adversaries may use this technique in conjunction with administrator-level Valid Accounts to remotely access a networked system over SMB, to interact with systems using remote procedure calls (RPCs), transfer files, and run transferred binaries through remote Execution. Example execution techniques that rely on authenticated sessions over SMB/RPC are Scheduled Task/Job, Service Execution, and Windows Management Instrumentation. Adversaries can also use NTLM hashes to access administrator shares on systems with Pass the Hash and certain configuration and patch levels.
T1021.003: Distributed Component Object Model
Adversaries may use Valid Accounts to interact with remote machines by taking advantage of Distributed Component Object Model (DCOM). The adversary may then perform actions as the logged-on user. The Windows Component Object Model (COM) is a component of the native Windows application programming interface (API) that enables interaction between software objects, or executable code that implements one or more interfaces. Through COM, a client object can call methods of server objects, which are typically Dynamic Link Libraries (DLL) or executables (EXE). Distributed COM (DCOM) is transparent middleware that extends the functionality of COM beyond a local computer using remote procedure call (RPC) technology. Permissions to interact with local and remote server COM objects are specified by access control lists (ACL) in the Registry. By default, only Administrators may remotely activate and launch COM objects through DCOM. Through DCOM, adversaries operating in the context of an appropriately privileged user can remotely obtain arbitrary and even direct shellcode execution through Office applications as well as other Windows objects that contain insecure methods. DCOM can also execute macros in existing documents and may also invoke Dynamic Data Exchange (DDE) execution directly through a COM created instance of a Microsoft Office application, bypassing the need for a malicious document. DCOM can be used as a method of remotely interacting with Windows Management Instrumentation.
T1021.004: SSH
Adversaries may use Valid Accounts to log into remote machines using Secure Shell (SSH). The adversary may then perform actions as the logged-on user. SSH is a protocol that allows authorized users to open remote shells on other computers. Many Linux and macOS versions come with SSH installed by default, although typically disabled until the user enables it. On ESXi, SSH can be enabled either directly on the host (e.g., via `vim-cmd hostsvc/enable_ssh`) or via vCenter. The SSH server can be configured to use standard password authentication or public-private keypairs in lieu of or in addition to a password. In this authentication scenario, the user’s public key must be in a special file on the computer running the server that lists which keypairs are allowed to login as that user (i.e., SSH Authorized Keys).
T1021.005: VNC
Adversaries may use Valid Accounts to remotely control machines using Virtual Network Computing (VNC). VNC is a platform-independent desktop sharing system that uses the RFB (“remote framebuffer”) protocol to enable users to remotely control another computer’s display by relaying the screen, mouse, and keyboard inputs over the network. VNC differs from Remote Desktop Protocol as VNC is screen-sharing software rather than resource-sharing software. By default, VNC uses the system's authentication, but it can be configured to use credentials specific to VNC. Adversaries may abuse VNC to perform malicious actions as the logged-on user such as opening documents, downloading files, and running arbitrary commands. An adversary could use VNC to remotely control and monitor a system to collect data and information to pivot to other systems within the network. Specific VNC libraries/implementations have also been susceptible to brute force attacks and memory usage exploitation.
T1021.006: Windows Remote Management
Adversaries may use Valid Accounts to interact with remote systems using Windows Remote Management (WinRM). The adversary may then perform actions as the logged-on user. WinRM is the name of both a Windows service and a protocol that allows a user to interact with a remote system (e.g., run an executable, modify the Registry, modify services). It may be called with the `winrm` command or by any number of programs such as PowerShell. WinRM can be used as a method of remotely interacting with Windows Management Instrumentation.
T1021.007: Cloud Services
Adversaries may log into accessible cloud services within a compromised environment using Valid Accounts that are synchronized with or federated to on-premises user identities. The adversary may then perform management actions or access cloud-hosted resources as the logged-on user. Many enterprises federate centrally managed user identities to cloud services, allowing users to login with their domain credentials in order to access the cloud control plane. Similarly, adversaries may connect to available cloud services through the web console or through the cloud command line interface (CLI) (e.g., Cloud API), using commands such as <code>Connect-AZAccount</code> for Azure PowerShell, <code>Connect-MgGraph</code> for Microsoft Graph PowerShell, and <code>gcloud auth login</code> for the Google Cloud CLI. In some cases, adversaries may be able to authenticate to these services via Application Access Token instead of a username and password.
T1021.008: Direct Cloud VM Connections
Adversaries may leverage Valid Accounts to log directly into accessible cloud hosted compute infrastructure through cloud native methods. Many cloud providers offer interactive connections to virtual infrastructure that can be accessed through the Cloud API, such as Azure Serial Console, AWS EC2 Instance Connect, and AWS System Manager.. Methods of authentication for these connections can include passwords, application access tokens, or SSH keys. These cloud native methods may, by default, allow for privileged access on the host with SYSTEM or root level access. Adversaries may utilize these cloud native methods to directly access virtual infrastructure and pivot through an environment. These connections typically provide direct console access to the VM rather than the execution of scripts (i.e., Cloud Administration Command).
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 T1021 Remote Services?
Adversaries may use Valid Accounts to log into a service that accepts remote connections, such as telnet, SSH, and VNC. The adversary may then perform actions as the logged-on user. In an enterprise environment, servers and workstations can be organized into domains. Domains provide centralized identity management, allowing users to login using one set of credentials across the entire network. If an adversary is able to obtain a set of valid domain credentials, they could login to many different machines using remote access protocols such as secure shell (SSH) or remote desktop protocol (RDP). They could also login to accessible SaaS or IaaS services, such as those that federate their identities to the domain, or management platforms for internal virtualization environments such as VMware vCenter. Legitimate applications (such as Software Deployment Tools and other administrative programs) may utilize Remote Services to access remote hosts. For example, Apple Remote Desktop (ARD) on macOS is native software used for remote management. ARD leverages a blend of protocols, including VNC to send the screen and control buffers and SSH for secure file transfer. Adversaries can abuse applications such as ARD to gain remote code execution and perform lateral movement. In versions of macOS prior to 10.14, an adversary can escalate an SSH session to an ARD session which enables an adversary to accept TCC (Transparency, Consent, and Control) prompts without user interaction and gain access to data.
Which tactics does T1021 belong to?
T1021 maps to the Lateral Movement tactic.
Does TurboPentest test for 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
- Execution, Lateral MovementT1072: Software Deployment Tools
- Lateral MovementT1080: Taint Shared Content
- Initial Access, Lateral MovementT1091: Replication Through Removable Media
- Lateral MovementT1210: Exploitation of Remote Services
- Lateral MovementT1534: Internal Spearphishing
- Lateral MovementT1550: Use Alternate Authentication Material
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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