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Windows Mail Protocol In Non-Common Process Path

The following analytic detects a Windows application establishing an SMTP connection from a non-common installation path. It leverages Sysmon EventCode 3 to identify processes not typically associated with email…

Description

The following analytic detects a Windows application establishing an SMTP connection from a non-common installation path. It leverages Sysmon EventCode 3 to identify processes not typically associated with email clients (e.g., Thunderbird, Outlook) making SMTP connections. This activity is significant as adversaries, including malware like AgentTesla, use such connections for Command and Control (C2) communication to exfiltrate stolen data. If confirmed malicious, this behavior could lead to unauthorized data exfiltration, including sensitive information like desktop screenshots, browser data, and system details, compromising the affected host.

Detection logic

Detection requirements

Platform
LinuxmacOSNetwork DevicesWindows

The rule states no platform. This is derived from the ATT&CK technique it maps to.

Log source category
sysmon_eventid_3

Known benign triggers

  • Third party email or SMTP based applications will trigger this. Apply additional filters as needed. Also consider excluding known email or any SMTP based clients installed outside of the Program Files and Windows directories.

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