Suspicious sending domain with sender address randomization

Synopsis

Field	Value
Activation Period	14 Days
Training Period	30 Days
Test Period	30 Minutes
Deduplication Period	1 Day
Required Data	Microsoft 365 Emails
Detection Modules	Email
Detector Tags	Phishing
ATT&CK Tactic	Initial Access (TA0001)
ATT&CK Technique	Phishing (T1566)
Severity	Informational

Description

Multiple messages from a single sender domain were observed over a short period, each using a unique sender address. This per-message sender randomization is uncommon for legitimate senders and suggests automated behavior.

Attacker's Goals

Trick the user into clicking a link, while avoiding detection.

Investigative actions

• Examine the sender's IP address and reputation.
• Verify whether the sender's IP address has appeared in different log sources before, and if it is recognizable.
• If the message contains attachments or links, scrutinize them for any suspicious indications.
• Monitor further actions taken, such as file downloads or access to potentially malicious links.

Variations

High-volume sender domain with per-message sender randomization

Synopsis

Field	Value
ATT&CK Tactic	Initial Access (TA0001)
ATT&CK Technique	Phishing (T1566)
Severity	Informational

Description

A high volume of emails was observed from a single sending domain over a short time period, each using a unique sender address. This high volume per-message sender randomization is uncommon for legitimate senders and suggests automated behavior.

Attacker's Goals

Trick the user into clicking a link, while avoiding detection.

Investigative actions

• Examine the sender's IP address and reputation.
• Verify whether the sender's IP address has appeared in different log sources before, and if it is recognizable.
• If the message contains attachments or links, scrutinize them for any suspicious indications.
• Monitor further actions taken, such as file downloads or access to potentially malicious links.