T1564.008: Email Hiding Rules — MITRE ATT&CK Technique

Description

Adversaries may use email rules to hide inbound emails in a compromised user's mailbox. Many email clients allow users to create inbox rules for various email functions, including moving emails to other folders, marking emails as read, or deleting emails. Rules may be created or modified within email clients or through external features such as the New-InboxRule or Set-InboxRule PowerShell cmdlets on Windows systems.(Citation: Microsoft Inbox Rules)(Citation: MacOS Email Rules)(Citation: Microsoft New-InboxRule)(Citation: Microsoft Set-InboxRule)

Adversaries may utilize email rules within a compromised user's mailbox to delete and/or move emails to less noticeable folders. Adversaries may do this to hide security alerts, C2 communication, or responses to Internal Spearphishing emails sent from the compromised account.

Any user or administrator within the organization (or adversary with valid credentials) may be able to create rules to automatically move or delete emails. These rules can be abused to impair/delay detection had the email content been immediately seen by a user or defender. Malicious rules commonly filter out emails based on key words (such as malware, suspicious, phish, and hack) found in message bodies and subject lines. (Citation: Microsoft Cloud App Security)

In some environments, administrators may be able to enable email rules that operate organization-wide rather than on individual inboxes. For example, Microsoft Exchange supports transport rules that evaluate all mail an organization receives against user-specified conditions, then performs a user-specified action on mail that adheres to those conditions.(Citation: Microsoft Mail Flow Rules 2023) Adversaries that abuse such features may be able to automatically modify or delete all emails related to specific topics (such as internal security incident notifications).

Platforms

WindowsLinuxmacOSOffice Suite

Mitigations (1)

AuditM1047

Enterprise email solutions may have monitoring mechanisms that may include the ability to audit inbox rules on a regular basis.

In an Exchange environment, Administrators can use Get-InboxRule / Remove-InboxRule and Get-TransportRule / Remove-TransportRule to discover and remove potentially malicious inbox and transport rules.(Citation: Microsoft Get-InboxRule)(Citation: Microsoft Manage

Threat Groups (2)

ID	Group	Context
G1015	Scattered Spider	[Scattered Spider](https://attack.mitre.org/groups/G1015) creates inbound rules on the compromised email accounts of security personnel to automatical...
G0085	FIN4	[FIN4](https://attack.mitre.org/groups/G0085) has created rules in victims' Microsoft Outlook accounts to automatically delete emails containing words...

References

Frequently Asked Questions

What is T1564.008 (Email Hiding Rules)?

T1564.008 is a MITRE ATT&CK technique named 'Email Hiding Rules'. It belongs to the Stealth tactic(s). Adversaries may use email rules to hide inbound emails in a compromised user's mailbox. Many email clients allow users to create inbox rules for various email functions, including moving emails to oth...

How can T1564.008 be detected?

Detection of T1564.008 (Email Hiding Rules) typically involves monitoring system logs, network traffic, and endpoint telemetry. Use SIEM rules, EDR solutions, and behavioral analytics to identify suspicious activity associated with this technique.

What mitigations exist for T1564.008?

There are 1 documented mitigations for T1564.008. Key mitigations include: Audit.

Which threat groups use T1564.008?

Known threat groups using T1564.008 include: Scattered Spider, FIN4.