Attack Chain

1. A user receives a malicious Microsoft Office document (e.g., Word, Excel) via email or downloads it from a compromised website.
2. The user opens the document, triggering the execution of a malicious macro or exploitation of a vulnerability within the Office application.
3. The Office application (e.g., winword.exe, excel.exe) spawns a suspicious child process such as cmd.exe or powershell.exe.
4. The spawned process executes a command to download a malicious payload from a remote server using bitsadmin.exe or certutil.exe.
5. The downloaded payload is a reverse shell or a malware dropper, which establishes a connection to an attacker-controlled server.
6. The attacker gains initial access to the compromised system and attempts to escalate privileges and perform reconnaissance.
7. The attacker uses discovery commands with net.exe, ipconfig.exe, tasklist.exe, and whoami.exe to map the environment and identify valuable targets.
8. The attacker moves laterally to other systems within the network, aiming to compromise critical assets and achieve their objectives, such as data theft or ransomware deployment.

Impact

Successful exploitation can lead to arbitrary code execution, allowing attackers to gain initial access to the compromised system. This can result in data theft, installation of malware, lateral movement to other systems, and ultimately, significant disruption to business operations. The widespread use of Microsoft Office makes it a prime target, potentially affecting a large number of users and organizations. Failure to detect and respond to these attacks can result in significant financial losses, reputational damage, and compromise of sensitive data.

Recommendation

• Enable process creation logging (Sysmon Event ID 1 or Windows Security Event Logs) to ensure the visibility required to detect suspicious child processes.
• Deploy the Sigma rule Suspicious MS Office Child Process to your SIEM and tune the rule based on your environment to reduce false positives.
• Investigate any alerts generated by the Suspicious MS Office Child Process Sigma rule by examining the parent process tree and associated network connections.
• Implement application control policies to restrict the execution of unauthorized processes from Microsoft Office applications.
• Regularly update Microsoft Office applications to patch known vulnerabilities.
• Block known malicious domains or IPs associated with malware delivery and command and control, based on threat intelligence feeds and IOCs from external sources.