Sarah Chen — Malware Reverse Engineer
Key Takeaways
- Phishing remains a prevalent initial access vector for ransomware attacks.
- Detailed behavioral analysis of the implant reveals sophisticated persistence mechanisms.
- Command and Control (C2) patterns indicate a strong affiliation with known ransomware-as-a-service operations.
Executive Summary
During our recent investigation of a ransomware attack affecting a mid-sized enterprise, we observed that the attackers employed phishing as the initial access vector. The attack leveraged an email that contained a malicious attachment, which, once executed, dropped a sophisticated implant that established a persistent foothold within the network. The subsequent stages of the attack showcased typical ransomware behavior, including lateral movement, data exfiltration, and encryption of critical files.
Initial Access
Initial access was gained through a phishing email that mimicked a legitimate invoice from a trusted supplier. The email contained a Microsoft Excel document with macro capabilities. Once users enabled macros—a common but dangerous decision—the embedded malicious code initiated the download of the dropper from a remote server controlled by the actor. Our analysis of the dropper revealed it to be a variant of Agent Tesla, which is known for its keylogging and credential harvesting features.
Execution & Persistence
Upon execution, the dropper wrote a secondary payload to the user’s temporary directory at %TEMP% empfile.exe and created a scheduled task to ensure persistence. Specifically, it created a task under the name Microsoft.Windows.Update using the command schtasks /create /tn
Source: Original Report