t1564-008-email-hiding-rules

name	T1564.008_email-hiding-rules
description	Adversaries may use email rules to hide inbound emails in a compromised user's mailbox.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1564.008","defense-evasion","windows","linux","macos","office-suite","sub-technique"]
technique_id	T1564.008
tactic	defense-evasion
all_tactics	["defense-evasion"]
platforms	["Windows","Linux","macOS","Office Suite"]
mitre_url	https://attack.mitre.org/techniques/T1564/008
tech_stack	["windows","linux","macos","office"]
cwe_ids	["CWE-693"]
chains_with	["T1564","T1564.001","T1564.002","T1564.003","T1564.004","T1564.005","T1564.006","T1564.007","T1564.009","T1564.010","T1564.011","T1564.012","T1564.013","T1564.014"]
prerequisites	["T1564"]
severity_boost	{"T1564":"Chain with T1564 for deeper attack path","T1564.001":"Chain with T1564.001 for deeper attack path","T1564.002":"Chain with T1564.002 for deeper attack path"}

T1564.008 Email Hiding Rules

Sub-technique of: T1564

High-Level 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.

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.

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. 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).

Kill Chain Phase

• Defense Evasion (TA0005)

Platforms: Windows, Linux, macOS, Office Suite

What to Check

• Identify if Email Hiding Rules technique is applicable to target environment
• Check Windows systems for indicators of Email Hiding Rules
• Check Linux systems for indicators of Email Hiding Rules
• Check macOS systems for indicators of Email Hiding Rules
• Verify mitigations are bypassed or absent (1 known mitigations)
• Assess detection coverage (1 detection strategies)