Indicator Removal: Clear Mailbox Data

Adversaries may modify mail and mail application data to remove evidence of their activity. Email applications allow users and other programs to export and delete mailbox data via command line tools or use of APIs. Mail application data can be emails, email metadata, or logs generated by the application or operating system, such as export requests.

Adversaries may manipulate emails and mailbox data to remove logs, artifacts, and metadata, such as evidence of Phishing/Internal Spearphishing, Email Collection, Mail Protocols for command and control, or email-based exfiltration such as Exfiltration Over Alternative Protocol. For example, to remove evidence on Exchange servers adversaries have used the ExchangePowerShell PowerShell module, including Remove-MailboxExportRequest to remove evidence of mailbox exports.[1][2] On Linux and macOS, adversaries may also delete emails through a command line utility called mail or use AppleScript to interact with APIs on macOS.[3][4]

Adversaries may also remove emails and metadata/headers indicative of spam or suspicious activity (for example, through the use of organization-wide transport rules) to reduce the likelihood of malicious emails being detected by security products.[5]

ID: T1070.008
Sub-technique of:  T1070
Tactic: Defense Evasion
Platforms: Google Workspace, Linux, Office 365, Windows, macOS
Contributors: Liran Ravich, CardinalOps
Version: 1.1
Created: 08 July 2022
Last Modified: 12 April 2023

Procedure Examples

ID Name Description
S0477 Goopy

Goopy has the ability to delete emails used for C2 once the content has been copied.[3]

C0024 SolarWinds Compromise

During the SolarWinds Compromise, APT29 removed evidence of email export requests using Remove-MailboxExportRequest.[1]

Mitigations

ID Mitigation Description
M1047 Audit

In an Exchange environment, Administrators can use Get-TransportRule / Remove-TransportRule to discover and remove potentially malicious transport rules.[6]

M1029 Remote Data Storage

Automatically forward mail data and events to a log server or data repository to prevent conditions in which the adversary can locate and manipulate data on the local system. When possible, minimize time delay on event reporting to avoid prolonged storage on the local system.

M1022 Restrict File and Directory Permissions

Protect generated event files that are stored locally with proper permissions and authentication and limit opportunities for adversaries to increase privileges by preventing Privilege Escalation opportunities.

Detection

ID Data Source Data Component Detects
DS0015 Application Log Application Log Content

In environments using Exchange, monitor logs for the creation or modification of mail processing settings, such as transport rules.

DS0017 Command Command Execution

Monitor executed commands and arguments that may delete or alter generated artifacts on a host system, including logs or captured files such as quarantined emails. In Exchange environments, monitor for PowerShell cmdlets that may create or alter transport rules, such as New-TransportRule and Set-TransportRule.[6]

DS0022 File File Deletion

Monitor for deletion of generated artifacts on a host system, including logs or captured files such as quarantined emails.

On Windows 10, mail application data is stored in C:\Users\Username\AppData\Local\Comms\Unistore\data. On Linux, mail data is stored in /var/spool/mail or /var/mail. On macOS, mail data is stored in ~/Library/Mail.

File Modification

Monitor for changes made to generated artifacts on a host system, including logs or captured files such as quarantined emails.

On Windows 10, mail application data is stored in C:\Users\Username\AppData\Local\Comms\Unistore\data. On Linux, mail data is stored in /var/spool/mail or /var/mail. On macOS, mail data is stored in ~/Library/Mail.

DS0009 Process Process Creation

Monitor for newly executed processes with arguments that may delete or alter generated artifacts on a host system, including logs or captured files such as quarantined emails.

References