Suspicious MS Outlook Child Process

This detection identifies suspicious child processes of Microsoft Outlook, often associated with spear phishing activity and the execution of malicious attachments. Attackers may leverage malicious documents delivered via email to execute arbitrary code on a victim’s machine. The rule focuses on identifying processes such as cmd.exe, powershell.exe, and other system binaries being spawned by Outlook, suggesting the potential execution of malicious attachments or exploitation for initial access. This activity is designed to bypass traditional security measures and gain an initial foothold within the targeted environment. The rule is designed for data generated by Elastic Defend, but also supports third-party data sources like CrowdStrike, Microsoft Defender XDR, SentinelOne Cloud Funnel, Sysmon, and Windows Security Event Logs.

Attack Chain

1. A user receives a spear phishing email with a malicious attachment (e.g., a Microsoft Office document or PDF).
2. The user opens the attachment, unknowingly triggering embedded malicious code (e.g., macros or exploits).
3. The malicious code executes within the context of Microsoft Outlook (outlook.exe).
4. The malicious code spawns a suspicious child process, such as cmd.exe, powershell.exe, mshta.exe, or wscript.exe.
5. The spawned process executes commands to download and execute further malicious payloads from external sources.
6. The downloaded payload establishes persistence on the compromised system.
7. The attacker gains initial access and begins reconnaissance activities.
8. The attacker moves laterally within the network, escalating privileges and compromising additional systems.

Impact

A successful attack can lead to initial access, allowing attackers to gain a foothold within the network, escalate privileges, and potentially exfiltrate sensitive data, deploy ransomware, or conduct other malicious activities. While specific victim counts and sectors are unavailable, similar attacks have targeted a wide range of industries.

Recommendation

• Deploy the Sigma rule “Suspicious MS Outlook Child Process Spawning Command Interpreter” to your SIEM to detect potential initial access attempts (see rule below).
• Enable Sysmon process creation logging (Event ID 1) to provide the necessary data for the Sigma rules.
• Block the execution of commonly abused system binaries (e.g., cmd.exe, powershell.exe, wscript.exe) as child processes of Outlook using application control policies where possible.
• Implement and enforce strict macro policies in Microsoft Office applications to prevent the execution of malicious code within documents.
• Regularly review and update email security policies to prevent spear phishing emails from reaching users.