Office Application Startup: Add-ins

Adversaries may abuse Microsoft Office add-ins to obtain persistence on a compromised system. Office add-ins can be used to add functionality to Office programs. [1] There are different types of add-ins that can be used by the various Office products; including Word/Excel add-in Libraries (WLL/XLL), VBA add-ins, Office Component Object Model (COM) add-ins, automation add-ins, VBA Editor (VBE), Visual Studio Tools for Office (VSTO) add-ins, and Outlook add-ins. [2][3]

Add-ins can be used to obtain persistence because they can be set to execute code when an Office application starts.

ID: T1137.006
Sub-technique of:  T1137
Tactic: Persistence
Platforms: Office 365, Windows
Permissions Required: Administrator, User
Data Sources: File monitoring, Process command-line parameters, Process monitoring, Windows Registry
Version: 1.0
Created: 07 November 2019
Last Modified: 26 March 2020

Procedure Examples

Name Description
Naikon

Naikon has used the RoyalRoad exploit builder to drop a second stage loader, intel.wll, into the Word Startup folder on the compromised host.[4]

Mitigations

This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.

Detection

Monitor and validate the Office trusted locations on the file system and audit the Registry entries relevant for enabling add-ins.[5][2]

Collect process execution information including process IDs (PID) and parent process IDs (PPID) and look for abnormal chains of activity resulting from Office processes. Non-standard process execution trees may also indicate suspicious or malicious behavior

References