Unusual attachment volume in outbound emails

Synopsis

Field	Value
Activation Period	14 Days
Training Period	30 Days
Test Period	10 Minutes
Deduplication Period	1 Hour
Required Data	Microsoft 365 Emails
Detection Modules	Email
Detector Tags	Exfiltration
ATT&CK Tactic	Exfiltration (TA0010)
ATT&CK Technique	Exfiltration Over Alternative Protocol (T1048)
Severity	Informational

Description

Numerous emails with substantial attachments sent by an internal sender to one or more external recipients within a short timeframe.

Attacker's Goals

• Extracting valuable information outside the company.
• Bypass Data Loss Prevention (DLP) by splitting data across multiple emails.

Investigative actions

• Check the content of the email that was 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 action taken, such as accessing to private keys, API tokens and sensitive data.

Variations

Unusual attachment volume in outbound emails to a single external recipient

Synopsis

Field	Value
ATT&CK Tactic	Exfiltration (TA0010)
ATT&CK Technique	Exfiltration Over Alternative Protocol (T1048)
Severity	Informational

Description

Numerous emails with substantial attachments sent by internal sender to one external recipient within a short timeframe.

Attacker's Goals

• Extracting valuable information outside the company.
• Bypass Data Loss Prevention (DLP) by splitting data across multiple emails.

Investigative actions

• Check the content of the email that was 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 action taken, such as accessing to private keys, API tokens and sensitive data.

Unusual attachment amount and size in outbound emails

Synopsis

Field	Value
ATT&CK Tactic	Exfiltration (TA0010)
ATT&CK Technique	Exfiltration Over Alternative Protocol (T1048)
Severity	Informational

Description

Numerous emails with substantial attachments sent by an internal sender to one or more external recipients within a short timeframe.

Attacker's Goals

• Extracting valuable information outside the company.
• Bypass Data Loss Prevention (DLP) by splitting data across multiple emails.

Investigative actions

• Check the content of the email that was 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 action taken, such as accessing to private keys, API tokens and sensitive data.