C2Looper Uses GitHub C2 in Suspected Ransomware Operations

Summary

C2Looper is a newly identified Rust-based malware family that functions as a backdoor and is likely associated with ransomware operations. It supports remote shell execution, system reconnaissance, persistence, and delivery of second-stage payloads. Newer variants have evolved to use GitHub as command-and-control infrastructure.

Investigation

ThreatLabz identified C2Looper through analysis of its binary behavior and network communication. Researchers observed two primary variants: an earlier version using plaintext HTTP for C2 and a newer v2 build that relies on GitHub for command-and-control operations. The investigation also documented command structures, string encryption techniques, and the shift from traditional HTTP endpoints to GitHub-hosted JSON files.

Mitigation

Detection should focus on unusual outbound GitHub connections used for non-standard activity and suspicious files appearing in user directories. Security teams should monitor for unexpected child processes of OneDrive and unauthorized execution of cmd.exe or PowerShell. Applying zero-trust principles can also help restrict the backdoor’s lateral movement capabilities.

Response

If C2Looper activity is detected, the affected host should be isolated immediately to prevent lateral movement or ransomware deployment. Suspicious OneDrive-related processes and unauthorized shell sessions should be terminated. Responders should also perform forensic analysis to identify the initial access vector, including possible ClickFix-style social engineering activity.

Simulation Execution

Prerequisite: The Telemetry & Baseline Pre-flight Check must have passed.

Rationale: This section details the precise execution of the adversary technique (TTP) designed to trigger the detection rule. The commands and narrative MUST directly reflect the TTPs identified and aim to generate the exact telemetry expected by the detection logic. Abstract or unrelated examples will lead to misdiagnosis.

• Attack Narrative & Commands: The adversary is attempting to establish a foothold using a technique observed in C2Looper malware. Instead of executing a binary directly, they use cmd.exe to pass specific API function names in the command line arguments. This is an attempt to use “Living-off-the-Land” (LotL) techniques to prepare for subsequent stages of a payload, such as dynamic resolution of functions like LoadLibrary to evade static analysis. By passing these strings through the command line, the adversary hopes to trigger a scripted loader that will eventually resolve these functions in memory.

• Regression Test Script:

  # Simulation of C2Looper-style command line arguments to trigger the rule
  # This attempts to trigger the (selection_process and selection_api) logic
  
  Write-Host "[+] Starting C2Looper API Function Simulation..." -ForegroundColor Cyan
  
  # Scenario 1: Triggering via LoadLibrary/GetProcAddress
  Write-Host "[+] Executing Scenario 1: API Function Names in CommandLine..." -ForegroundColor Yellow
  Start-Process cmd.exe -ArgumentList "/c echo Triggering LoadLibrary and GetProcAddress usage"
  
  # Scenario 2: Triggering via ShellExecuteW
  Write-Host "[+] Executing Scenario 2: ShellExecuteW in CommandLine..." -ForegroundColor Yellow
  Start-Process cmd.exe -ArgumentList "/c echo Testing ShellExecuteW pattern"
  
  Write-Host "[+] Simulation Complete. Check SIEM for alerts." -ForegroundColor Green

• Cleanup Commands:

  # No persistent changes made by the simulation; no cleanup required.
  Write-Host "[+] No cleanup required." -ForegroundColor Cyan