Exchange transport forwarding rule configured

Synopsis

Field	Value
Activation Period	14 Days
Training Period	30 Days
Test Period	N/A (single event)
Deduplication Period	1 Day
Required Data	Office 365 Audit
Detection Modules	Identity Threat Module, SaaS Threat Detection, Email
ATT&CK Tactic	Collection (TA0009), Exfiltration (TA0010)
ATT&CK Technique	Email Collection: Email Forwarding Rule (T1114.003), Automated Exfiltration (T1020), Email Collection (T1114)
Severity	Low

Description

A user configured an Exchange transport (mail flow) forwarding rule, which is applied to all emails that match certain conditions in the organization.

Attacker's Goals

Forward all emails in the organization that match specific criteria to an external recipient to collect sensitive information.

Investigative actions

• Check what mailboxes are affected by the transport rule.
• Look for signs that the user account and mailbox are compromised (e.g. abnormal logins, unusual activity).
• Check if the forwarding domain is an unknown external domain and look up its reputation.
• Investigate the IP address associated with the rule.
• Follow further actions done by the account.
• Check for a possible phishing campaign on the organization.
• Look for emails sent to this recipient by other users.

Variations

Exchange transport forwarding rule configured by a delegate user

Synopsis

Field	Value
ATT&CK Tactic	Collection (TA0009), Exfiltration (TA0010)
ATT&CK Technique	Email Collection: Email Forwarding Rule (T1114.003), Automated Exfiltration (T1020), Email Collection (T1114)
Severity	Informational

Description

A user configured an Exchange transport (mail flow) forwarding rule, which is applied to all emails that match certain conditions in the organization. The user who set the forwarding is a delegated user, who performed this action on behalf of another user.

Attacker's Goals

Forward all emails in the organization that match specific criteria to an external recipient to collect sensitive information.

Investigative actions

• Check what mailboxes are affected by the transport rule.
• Look for signs that the user account and mailbox are compromised (e.g. abnormal logins, unusual activity).
• Check if the forwarding domain is an unknown external domain and look up its reputation.
• Investigate the IP address associated with the rule.
• Follow further actions done by the account.
• Check for a possible phishing campaign on the organization.
• Look for emails sent to this recipient by other users.

Suspicious Exchange transport forwarding rule configured

Synopsis

Field	Value
ATT&CK Tactic	Collection (TA0009), Exfiltration (TA0010)
ATT&CK Technique	Email Collection: Email Forwarding Rule (T1114.003), Automated Exfiltration (T1020), Email Collection (T1114)
Severity	Medium

Description

A user configured an Exchange transport (mail flow) forwarding rule, which is applied to all emails that match certain conditions in the organization.

Attacker's Goals

Forward all emails in the organization that match specific criteria to an external recipient to collect sensitive information.

Investigative actions

• Check what mailboxes are affected by the transport rule.
• Look for signs that the user account and mailbox are compromised (e.g. abnormal logins, unusual activity).
• Check if the forwarding domain is an unknown external domain and look up its reputation.
• Investigate the IP address associated with the rule.
• Follow further actions done by the account.
• Check for a possible phishing campaign on the organization.
• Look for emails sent to this recipient by other users.