Mike Torres — Incident Response Specialist
Key Takeaways
- Understanding the attack vector used in the initial access phase.
- Identification of persistence mechanisms leveraged by the malware.
- Exploring C2 communication strategies for effective detection.
Executive Summary
During our investigation of a recent ransomware attack, we observed a sophisticated adversary leveraging a multi-faceted approach to infiltrate corporate networks. The attackers utilized phishing emails as their entry point, deploying a trojanized document that delivered the ransomware implant. Our analysis revealed a systematic approach to the attack lifecycle, from initial access through to data exfiltration and ransom demand.
Initial Access
The initial access vector was primarily through carefully crafted phishing emails that included embedded macros in documents. When opened, these documents exhibited behavior consistent with the use of Phishing (T1566). Users were prompted to enable macros, which then triggered the execution of PowerShell commands that fetched the malicious payload from a remote URL. The sample we examined was hosted on a compromised website and had an MD5 hash of 9f24c92445d4e9c2ghyan7ud0g23a52e.
Execution & Persistence
Upon execution, the ransomware utilized several techniques to ensure persistence. We identified a registry key modification during our analysis, specifically HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\malicious_ransomware, which was used to reinstate the payload on system reboot. The dropper also created a scheduled task named MaliciousTask that executed the payload every hour. This clever combination of techniques exemplifies the use of Startup Items (T1547.001).
Command and Control
The ransomware implemented a robust command and control mechanism that utilized encrypted communication over HTTPS. It beaconed to an endpoint identified as https://malicious.c2server.com, employing Application Layer Protocol (T1071) to evade detection. The analytics suggested that the malware utilized a unique identifier for each infected host, allowing the actors to command and control various compromised machines without raising suspicion.
Lateral Movement & Discovery
Lateral movement was achieved using Windows Admin Shares (T1077) and Remote Services (T1021). The attackers leveraged Windows Management Instrumentation (WMI) calls to gather intelligence about network shares and credentials stored in memory. Our investigation revealed that the malware made use of the net use command to facilitate access to shared network drives, attempting to spread the ransomware to critical databases.
Impact & Objectives
The ultimate impact was significant, leading to widespread data encryption and business disruption. The threat actor’s primary objective appeared to be financial gain, supported by the ransom note left on the compromised systems demanding payment in cryptocurrency. We identified network logs indicating data exfiltration prior to encryption, suggesting that they were not only looking to monetize through ransoms but also to leverage sensitive data.
MITRE ATT&CK Mapping
- T1566 – Phishing: Initial access through phishing emails delivering malicious documents.
- T1071 – Application Layer Protocol: C2 communications over HTTPS.
- T1547.001 – Registry Run Keys / Startup Folder: Persistence via registry modifications.
- T1077 – Windows Admin Shares: Lateral movement through network shares.
- T1021 – Remote Services: Use of remote services for lateral movement.
Detection Opportunities
- Monitor for unusual registry key modifications related to startup items.
- Implement email filtering for suspicious attachments with macros.
- Analyze network traffic for unauthorized HTTP/HTTPS requests to known malicious domains.
Analyst Notes
This attack underscores the importance of continuous monitoring and the implementation of robust email security measures. Our investigation serves as a reminder that ransomware is evolving, adopting increasingly sophisticated tactics. Deploying indicators of compromise (IOCs) gathered during this analysis can significantly aid organizations in detecting and mitigating future threats. Comprehensive training for staff on recognizing phishing attempts remains a critical line of defense.
Source: Original Report