T1137.005sub-technique of T1137 Office Application Startup
Outlook Rules
Windows · Office Suitenothing on this site yetT1137.005 on attack.mitre.org
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.
If this is happening now
Checklists and playbooks to open while the alert is still live.
Playbook for this stage
Suspicious execution on an endpoint
An EDR alert, an unexplained process, or a user reporting something odd.
how MITRE says to see it
Detect Persistence via Malicious Outlook Rules
- Adversary uses a tool like Ruler or MFCMapi to create a malicious Outlook rule that triggers execution upon receipt of a crafted email. On email delivery, Outlook executes the rule, resulting in code execution (e.g., launching mshta.exe or PowerShell).
- Adversary adds a new Outlook rule with modified or obfuscated PR_RULE_MSG_NAME and PR_RULE_MSG_PROVIDER attributes using MFCMapi or Ruler. Rule is triggered when email arrives, executing embedded or external code. Mailbox audit logs or Unified Audit Log shows automated rule-triggered action without user interaction.
what reduces it
- 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.
- 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. Microsoft has released patches to try to address each issue.