Detection Strategy for Spearphishing via a Service across OS Platforms

ID: DET0115
Domains: Enterprise
Analytics: AN0320, AN0321, AN0322
Version: 1.0
Created: 21 October 2025
Last Modified: 21 October 2025

Analytics

AN0320

Inbound spearphishing attempts delivered via third-party services (e.g., Gmail, LinkedIn messages) leading to malicious file downloads or browser-initiated script execution. Defender view includes correlation of external service logins, unexpected file write operations, and suspicious descendant processes spawned from productivity or browser applications.

Log Sources
Data Component Name Channel
Process Creation (DC0032) WinEventLog:Security EventCode=4688
File Creation (DC0039) WinEventLog:Sysmon EventCode=11
Network Connection Creation (DC0082) WinEventLog:Sysmon EventCode=3
Mutable Elements
Field Description
MonitoredServices List of third-party services (e.g., Gmail, LinkedIn, Dropbox) relevant to the organization’s threat profile.
SuspiciousProcessPatterns Process lineage and parent-child execution relationships considered abnormal (e.g., outlook.exe → powershell.exe).
TimeWindow Correlates file creation and outbound connection activity within a tunable time period after message receipt.

AN0321

Use of non-enterprise email or messaging services in Thunderbird, Evolution, or browsers leading to suspicious file downloads and subsequent execution. Defender view includes browser-initiated downloads of unexpected content and shell or interpreter processes launched post-download.

Log Sources
Data Component Name Channel
Process Creation (DC0032) auditd:SYSCALL execve: Execution of bash, python, or perl processes spawned by browser/email client
Application Log Content (DC0038) linux:syslog Inbound messages from webmail services containing attachments or URLs
Network Traffic Flow (DC0078) NSM:Flow Outbound traffic to domains/IPs not previously resolved, occurring shortly after attachment download or link click
Mutable Elements
Field Description
BrowserProcesses Configured list of browsers or email clients to monitor (e.g., firefox, chromium, thunderbird).
PhishingIndicators Custom regex rules for suspicious URL patterns, file extensions, or encoded links.

AN0322

Phishing attempts via iCloud Mail, Gmail, or social media apps accessed on macOS systems. Defender view includes Mail.app or Safari downloads of files followed by osascript, Terminal, or abnormal child process execution.

Log Sources
Data Component Name Channel
Application Log Content (DC0038) macos:unifiedlog Received messages containing embedded links or attachments from non-enterprise services
Process Creation (DC0032) macos:unifiedlog Execution of osascript, bash, or Terminal initiated from Mail.app or Safari
Network Traffic Content (DC0085) macos:unifiedlog Suspicious outbound HTTPS requests to domains flagged as newly registered or untrusted after spearphishing message interaction
Mutable Elements
Field Description
CertificateChecks Flagging mismatched or self-signed certificates during outbound connections initiated after spearphishing messages.
ExecutionDelay Window of time between attachment download and subsequent suspicious execution.