T1137.003 - Outlook Forms

Adversaries may abuse Microsoft Outlook forms to obtain persistence on a compromised system. Outlook forms are used as templates for presentation and functionality in Outlook messages. Custom Outlook forms can be created that will execute code when a specifically crafted email is sent by an adversary utilizing the same custom Outlook form.(Citation: SensePost Outlook Forms)

Once malicious forms have been added to the user’s mailbox, they will be loaded when Outlook is started. Malicious forms will execute when an adversary sends a specifically crafted email to the user.(Citation: SensePost Outlook Forms)

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Microsoft has released a PowerShell script to safely gather mail forwarding rules and custom forms in your mail environment as well as steps to interpret the output.(Citation: Microsoft Detect Outlook Forms) SensePost, whose tool Ruler can be used to carry out malicious rules, forms, and Home Page attacks, has released a tool to detect Ruler usage.(Citation: SensePost NotRuler)

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.