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Office Application Startup: Outlook Rules
Other sub-techniques of Office Application Startup (6)
| 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 rules to obtain persistence on a compromised system. Outlook rules allow a user to define automated behavior to manage email messages. A benign rule might, for example, automatically move an email to a particular folder in Outlook if it contains specific words from a specific sender. Malicious Outlook rules can be created that can trigger code execution when an adversary sends a specifically crafted email to that user.[1]
Once malicious rules have been added to the user’s mailbox, they will be loaded when Outlook is started. Malicious rules will execute when an adversary sends a specifically crafted email to the user.[1]
Procedure Examples
| Name | Description |
|---|---|
| Ruler |
Ruler can be used to automate the abuse of Outlook Rules to establish persistence.[2] |
Mitigations
| Mitigation | Description |
|---|---|
| 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.[3] 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] |
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.[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.
References
- Stalmans, E. (2017, October 11). Outlook Home Page – Another Ruler Vector. Retrieved February 4, 2019.
- Fox, C., Vangel, D. (2018, April 22). Detect and Remediate Outlook Rules and Custom Forms Injections Attacks in Office 365. Retrieved February 4, 2019.
- SensePost. (2017, September 21). NotRuler - The opposite of Ruler, provides blue teams with the ability to detect Ruler usage against Exchange. Retrieved February 4, 2019.