Detection Strategy for Spearphishing Attachment across OS Platforms

ID: DET0236
Domains: Enterprise
Analytics: AN0655, AN0656, AN0657
Version: 1.0
Created: 21 October 2025
Last Modified: 21 October 2025

Analytics

AN0655

Detection of spearphishing attachments by correlating suspicious email delivery with subsequent file creation and abnormal process execution (e.g., Office spawning PowerShell or CMD). Behavior chain includes inbound email metadata → attachment stored on disk → process execution → outbound network activity.

Log Sources
Data Component Name Channel
Application Log Content (DC0038) m365:unified Send/Receive: Inbound emails with attachments from suspicious or spoofed senders
File Creation (DC0039) WinEventLog:Sysmon EventCode=11
Process Creation (DC0032) WinEventLog:Sysmon EventCode=1
Network Connection Creation (DC0082) WinEventLog:Sysmon EventCode=3
Mutable Elements
Field Description
AttachmentExtensions List of high-risk extensions to monitor (e.g., .exe, .js, .vbs, .docm, .xlsm).
SuspiciousParentChildPairs Process lineage patterns considered malicious (e.g., winword.exe → powershell.exe).
TimeWindow Correlation window between email receipt, file creation, and process execution.

AN0656

Phishing attachments executed on Linux systems are detected by linking email logs to file creation in mail directories and subsequent suspicious process execution. Look for unexpected binaries or scripts spawned from user mail directories and anomalous outbound network activity.

Log Sources
Data Component Name Channel
Application Log Content (DC0038) Application:Mail Inbound email attachments logged from MTAs with suspicious metadata
Process Creation (DC0032) auditd:SYSCALL execve: Execution of files saved in mail or download directories
Network Traffic Flow (DC0078) NSM:Flow Outbound traffic from suspicious new processes post-attachment execution
Mutable Elements
Field Description
AttachmentStoragePaths Monitored directories for email attachments (e.g., /var/mail, ~/Maildir, ~/Downloads).
ScriptInterpreters List of interpreters to monitor when spawned by mail clients (e.g., bash, python, perl).

AN0657

Phishing attachment detection on macOS through correlation of Mail app logs, file creation in user directories, and abnormal process execution (e.g., Preview.app or Mail.app spawning Terminal or scripting binaries). Network traffic after attachment interaction is also monitored.

Log Sources
Data Component Name Channel
Application Log Content (DC0038) macos:unifiedlog Inbound messages with attachments from suspicious domains
Process Creation (DC0032) macos:unifiedlog Execution of Terminal, osascript, or other interpreters originating from Mail or Preview
File Creation (DC0039) macos:unifiedlog Attachment files written to ~/Downloads or temporary folders
Mutable Elements
Field Description
ExecutionDelayThreshold Time delay between attachment download and execution considered suspicious.
SuspiciousParentApps Parent processes expected to rarely spawn child processes (e.g., Mail.app, Preview.app).