The Nitrogen ransomware group uses malvertising and DLL sideloading to gain initial access, followed by Cobalt Strike for lateral movement and post-exploitation activities, often covering their tracks by clearing logs. Advanced forensic techniques such as crash dump analysis and custom YARA rules reveal detailed insights into their operations and pivoting tactics. #Nitrogen #CobaltStrike
Keypoints
- Nitrogen ransomware initially targeted the US and Canada before expanding to Africa and Europe, with many victims not publicly disclosed.
- The group used malvertising campaigns disguising malware as legitimate tools like WinSCP, Advanced IP Scanner, and FileZilla to establish initial access.
- A malicious ZIP containing a backdoored python312.dll and renamed python.exe enabled DLL sideloading, resulting in a stealthy infection.
- Detection of Cobalt Strike was made via forensic artifacts including Prefetch files, user access logs, and analysis of executables created on the day of infection.
- Windows Error Reporting (WER) crash dumps exposed in-memory Cobalt Strike beacon configurations and HTTP response details, proving useful for post-intrusion analysis.
- Attackers cleared critical Windows event logs to hinder detection, but user access logging helped track lateral movement between compromised hosts.
- Custom YARA rules leveraging XOR encryption patterns and known Cobalt Strike watermarks enabled identification of infected files and expanded threat hunting scope.
MITRE Techniques
- [T1027] Obfuscated Files or Information – Malicious DLL sideloading using a renamed python.exe and a fake python312.dll to evade detection (‘malicious python312.dll… mirrors the same exports and ordinals found in a genuine Python DLL’).
- [T1190] Exploit Public-Facing Application – Initial access via malvertising leading to compromised WordPress site hosting malicious WinSCP ZIP (‘redirected… to a compromised WordPress site hosting a malicious WinSCP ZIP file’).
- [T1071] Application Layer Protocol – Use of HTTP-based Cobalt Strike beacon communications revealed in crash dumps (‘Cobalt Strike HTTP Response in the svchost.exe crash dump’).
- [T1005] Data from Local System – Extraction and analysis of Windows Error Reporting (WER) crash dumps to obtain Cobalt Strike configuration strings (‘using Windows Error Reporting (WER) and crash dump files… uncovered a Cobalt Strike configuration’).
- [T1055] Process Injection – Post-compromise payload injection into gpupdate.exe and svchost.exe processes for stealth (‘gpupdate.exe was employed as sacrificial process for Cobalt Strike’).
- [T1076] Remote Desktop Protocol – Lateral movement tracked via User Access Logging despite cleared Windows event logs (‘User Access Logging (UAL) entries… provided clear evidence of lateral movement’).
- [T1070] Indicator Removal on Host – Threat actors cleared Security, System, and PowerShell logs to cover tracks (‘the threat actor had cleared critical Windows event logs’).
Indicators of Compromise
- [File Hash] Malicious ZIP and files – WinSCP-6.3.6-Setup.zip SHA-256: fa3eca4d53a1b7c4cfcd14f642ed5f8a8a864f56a8a47acbf5cf11a6c5d2afa2, legitimate python312.dll hash: 278f22e258688a2afc1b6ac9f3aba61be0131b0de743c74db1607a7b6b934043.
- [Domain] Initial access redirect – ftp-winscp[.]org and compromised WordPress site hosting malicious WinSCP ZIP.
- [Executable Names] Suspicious processes – Intel64.exe, tcpp.exe, IntelGup.exe, gpupdate.exe (used as sacrificial process), svchost.exe with embedded Cobalt Strike activity.
- [IP Address] Internal pivot IP – 192.168.101.XXX (corresponding to patient zero’s internal IP, port 5000 used for C2 communication).
- [YARA Rules] Custom rule based on encrypted strings of gpupdate.exe paths and Cobalt Strike watermark 678358251 for detecting Cobalt Strike configurations.