Remote Services: 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.[1][2]

Permissions to interact with local and remote server COM objects are specified by access control lists (ACL) in the Registry.[3] By default, only Administrators may remotely activate and launch COM objects through DCOM.[4]

Through DCOM, adversaries operating in the context of an appropriately privileged user can remotely obtain arbitrary and even direct shellcode execution through Office applications[5] as well as other Windows objects that contain insecure methods.[6][7] DCOM can also execute macros in existing documents[8] and may also invoke Dynamic Data Exchange (DDE) execution directly through a COM created instance of a Microsoft Office application[9], bypassing the need for a malicious document.

ID: T1021.003
Sub-technique of:  T1021
Tactic: Lateral Movement
Platforms: Windows
Permissions Required: Administrator, SYSTEM
Data Sources: API monitoring, Authentication logs, DLL monitoring, Packet capture, PowerShell logs, Process monitoring, Windows Registry, Windows event logs
Version: 1.0
Created: 11 February 2020
Last Modified: 23 March 2020

Procedure Examples

Name Description
Cobalt Strike

Cobalt Strike can deliver "beacon" payloads for lateral movement by leveraging remote COM execution.[13]

Empire

Empire can utilize Invoke-DCOM to leverage remote COM execution for lateral movement.[14]

Mitigations

Mitigation Description
Application Isolation and Sandboxing

Ensure all COM alerts and Protected View are enabled.[12]

Disable or Remove Feature or Program

Consider disabling DCOM through Dcomcnfg.exe.[11]

Network Segmentation

Enable Windows firewall, which prevents DCOM instantiation by default.

Privileged Account Management

Modify Registry settings (directly or using Dcomcnfg.exe) in HKEY_LOCAL_MACHINE\SOFTWARE\Classes\AppID\{{{{AppID_GUID}}}} associated with the process-wide security of individual COM applications.[3]

Modify Registry settings (directly or using Dcomcnfg.exe) in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole associated with system-wide security defaults for all COM applications that do not set their own process-wide security.[10] [4]

Detection

Monitor for COM objects loading DLLs and other modules not typically associated with the application.[5] Enumeration of COM objects, via Query Registry or PowerShell, may also proceed malicious use.[1][6] Monitor for spawning of processes associated with COM objects, especially those invoked by a user different than the one currently logged on.

Monitor for any influxes or abnormal increases in Distributed Computing Environment/Remote Procedure Call (DCE/RPC) traffic.

References