| ID | Name |
|---|---|
| T1137.001 | Office Template Macros |
| T1137.002 | Office Test |
| T1137.003 | Outlook Forms |
| T1137.004 | Outlook Home Page |
| T1137.005 | Outlook Rules |
| T1137.006 | Add-ins |
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.[1]
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.[1]
| ID | Name | Description |
|---|---|---|
| S0358 | Ruler |
Ruler can be used to automate the abuse of Outlook Forms to establish persistence.[2] |
| ID | Mitigation | Description |
|---|---|---|
| M1040 | Behavior Prevention on Endpoint |
On Windows 10, enable Attack Surface Reduction (ASR) rules to prevent Office applications from creating child processes and from writing potentially malicious executable content to disk. [3] |
| M1051 | Update Software |
For the Outlook methods, blocking macros may be ineffective as the Visual Basic engine used for these features is separate from the macro scripting engine.[1] Microsoft has released patches to try to address each issue. Ensure KB3191938 which blocks Outlook Visual Basic and displays a malicious code warning, KB4011091 which disables custom forms by default, and KB4011162 which removes the legacy Home Page feature, are applied to systems.[4] |
| ID | Data Source | Data Component |
|---|---|---|
| DS0015 | Application Log | Application Log Content |
| DS0017 | Command | Command Execution |
| DS0009 | Process | Process Creation |
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.[5] 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.[6]
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.