Sending unusual file(s) to an external address

Synopsis

Field	Value
Activation Period	14 Days
Training Period	30 Days
Test Period	N/A (single event)
Deduplication Period	1 Hour 30 Minutes
Required Data	Microsoft 365 Emails
Detection Modules	Email
Detector Tags	Exfiltration
ATT&CK Tactic	Initial Access (TA0001), Exfiltration (TA0010)
ATT&CK Technique	Phishing (T1566), Exfiltration Over Alternative Protocol (T1048)
Severity	Low

Description

Unusual files sent to an external address.

Attacker's Goals

• Extracting sensitive credentials, potentially leading to account takeover or unauthorized access to internal services.
• Extracting valuable information outside the company.

Investigative actions

• Check the content of the unusual files that were sent.
• Review the external recipient address and assess its reputation.
• Review past emails sent from this mailbox for any suspicious activity.
• Check for unusual emails sent to this recipient's address.
• Monitor further actions taken, such as accessing private keys, API tokens and sensitive data.