BlackSun Ransomware: PowerShell Kill Chain to Encryption
| Report ID | INC2022-0516-PSE | Classification | Simulated / Training Environment |
| Analyst | F. Nanos | Platform / Tool | TryHackMe ยท Splunk (Sysmon) |
| Severity | Critical | Status | Closed (Investigation Complete) |
| Impact | Confirmed file encryption (availability impact) | ||
1. Executive Summary
A workstation was compromised and encrypted by BlackSun ransomware. The attack began with a single obfuscated PowerShell command that disabled real-time antivirus monitoring, downloaded a dropper through a public tunneling service, and scheduled it to run with SYSTEM privileges. The dropper then contacted an external command-and-control endpoint, retrieved the ransomware payload, encrypted the user's files, and replaced the desktop wallpaper with a ransom message. The full chain was reconstructed from Sysmon telemetry in Splunk. This was a successful detonation with real availability impact; recovery depends on clean offline backups.
2. Scope & Methodology
The investigation was conducted against Sysmon endpoint telemetry in Splunk. The initiating action was a Base64-encoded PowerShell command; because PowerShell encodes such commands in UTF-16LE, the decode path was Base64 followed by UTF-16LE text decoding, which revealed the full malicious sequence. Process-creation, file-creation, and DNS-query event types were then correlated to trace delivery, C2, and encryption.
3. Attack Chain
3.1 Obfuscated PowerShell & Defender Disable
The decoded command first turned off Windows Defender real-time monitoring, removing the endpoint's primary protection before any payload touched disk.
Set-MpPreference -DisableRealtimeMonitoring $true3.2 Dropper Delivery via Tunneling Service
The command downloaded a dropper executable into a system temporary directory through a public tunneling service. Fronting the real infrastructure with a legitimate-looking tunnel domain defeats IP and domain reputation controls.
3.3 SYSTEM-Level Scheduled Task
A scheduled task was created to execute the dropper as SYSTEM. This grants the highest privilege on the host without any credential theft, and simultaneously provides execution persistence.
SCHTASKS /Create /TN [dropper] /RU SYSTEM ...3.4 C2 & Ransomware Deployment
The dropper contacted a second tunnel endpoint and retrieved the BlackSun ransomware as a PowerShell script. The payload encrypted the user's files, dropped a ransom note into the user's Downloads directory, and set a ransom-themed image as the desktop wallpaper, the visible confirmation of a successful event.
4. Detection Queries
Each query below was used during the investigation to surface a specific stage of the chain.
# 1 - Encoded PowerShell parent command lines (exposes the -enc launcher)
index=main EventCode=1
| stats count by ParentCommandLine
# 2 - Dropped files (locates the dropper in the temp directory)
index=main EventCode=11
| stats count by TargetFilename, Image
# 3 - C2 via DNS (tunnel traffic is invisible to IP reputation; DNS is the tell)
index=main EventCode=22 [dropper]
| table QueryName, Image
# 4 - Ransomware artifacts (confirms family and encryption event)
index=main EventCode=11 TargetFilename="*BlackSun*"
| table TargetFilename, Image5. MITRE ATT&CK Mapping
| Technique ID | Technique | Tactic |
|---|---|---|
| T1059.001 | PowerShell | Execution |
| T1027.010 | Command Obfuscation (Base64) | Defense Evasion |
| T1562.001 | Impair Defenses: Disable or Modify Tools | Defense Evasion |
| T1105 | Ingress Tool Transfer | Command and Control |
| T1071 | Application Layer Protocol (tunnel) | Command and Control |
| T1053.005 | Scheduled Task (SYSTEM) | Persistence |
| T1486 | Data Encrypted for Impact | Impact |
6. Recommendations
- Isolate and rebuild the affected host; restore encrypted data from offline backups. Do not consider payment.
- Enable Windows Defender Tamper Protection so real-time monitoring cannot be disabled from a script.
- Enforce PowerShell Constrained Language Mode and Script Block Logging.
- Restrict or monitor outbound access to public tunneling services at the egress.
- Alert on encoded PowerShell command lines, on the Defender real-time-disable command, and on DNS queries to known tunneling domains.
- Alert on scheduled tasks created with SYSTEM run-level that point to binaries in temporary directories.
7. Investigator's Notes
Two points proved most instructive. First, the tunneling-based C2 was effectively invisible to IP-reputation controls, so DNS-query telemetry, not network-reputation blocking, was the dependable detection. Second, benign PowerShell policy-test artifacts appeared alongside the malicious activity and had to be recognized as legitimate noise rather than pursued as indicators. The standing lesson is that a full ransomware chain can hinge on a single decoded command, and that decoding obfuscated PowerShell early is often the fastest route to the entire kill chain.