Google Workspace Custom Gmail Route Created or Modified

Elastic Stack Serverless Security

Detects when a custom Gmail route is added or modified in Google Workspace. Adversaries can add a custom e-mail route for outbound mail to route these e-mails to their own inbox of choice for data gathering. This allows adversaries to capture sensitive information from e-mail and potential attachments, such as invoices or payment documents. By default, all email from current Google Workspace users with accounts are routed through a domain’s mail server for inbound and outbound mail.

Rule type: query

Rule indices:

• filebeat-*
• logs-google_workspace*

Severity: medium

Risk score: 47

Runs every: 10m

Searches indices from: now-130m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

• https://support.google.com/a/answer/2685650?hl=en

Tags:

• Elastic
• Cloud
• Google Workspace
• Continuous Monitoring
• SecOps
• Collection

Version: 2

Rule authors:

• Elastic

Rule license: Elastic License v2

• As per Google's documentation, Google Workspace administrators may observe lag times ranging from minutes up to 3 days between the time of an event's occurrence and the event being visible in the Google Workspace admin/audit logs.
• This rule is configured to run every 10 minutes with a lookback time of 130 minutes.
• To reduce the risk of false negatives, consider reducing the interval that the Google Workspace (formerly G Suite) Filebeat module polls Google's reporting API for new events.
• By default, var.interval is set to 2 hours (2h). Consider changing this interval to a lower value, such as 10 minutes (10m).
• See the following references for further information:
  • https://support.google.com/a/answer/7061566
  • /beats/docs/reference/ingestion-tools/beats-filebeat/filebeat-module-google_workspace.md

event.dataset:"google_workspace.admin" and event.action:("CREATE_GMAIL_SETTING" or "CHANGE_GMAIL_SETTING")
  and google_workspace.event.type:"EMAIL_SETTINGS" and google_workspace.admin.setting.name:("EMAIL_ROUTE" or "MESSAGE_SECURITY_RULE")

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Collection
  • ID: TA0009
  • Reference URL: https://attack.mitre.org/tactics/TA0009/

• Technique:

  • Name: Email Collection
  • ID: T1114
  • Reference URL: https://attack.mitre.org/techniques/T1114/

• Sub-technique:

  • Name: Email Forwarding Rule
  • ID: T1114.003
  • Reference URL: https://attack.mitre.org/techniques/T1114/003/