Description
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.(Citation: SilentBreak Outlook Rules) 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.(Citation: SilentBreak Outlook Rules)
Threat-Mapped Scoring
Threat Score:
1.8
Industry:
Threat Priority:
P4 - Informational (Low)
ATT&CK Kill Chain Metadata
- Tactics: persistence
- Platforms: Windows, Office Suite
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Detection Guidance:
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) This PowerShell script is ineffective in gathering rules with modified `PRPR_RULE_MSG_NAME` and `PR_RULE_MSG_PROVIDER` properties caused by adversaries using a Microsoft Exchange Server Messaging API Editor (MAPI Editor), so only examination with the Exchange Administration tool MFCMapi can reveal these mail forwarding rules.(Citation: Pfammatter - Hidden Inbox Rules) SensePost, whose tool [Ruler](https://attack.mitre.org/software/S0358) 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.