BlackToad Uses Network Manipulation in an AutoIt Payload

SOC Prime Team

BlackToad Uses Network Manipulation in an AutoIt Payload

Detection stack

AIDR
Alert
ETL
Query

Threat Report
Attack Flow
Detections
Simulations

Summary

JUMPSEC uncovered a phishing campaign that delivers a Remcos RAT payload concealed inside a custom AutoIt crypter. The infection chain uses a VBS script to run ipconfig /release followed by ipconfig /renew, briefly disrupting network connectivity as a way to evade detection. Researchers linked the campaign to the Nigerian e-crime ecosystem, with infrastructure relying on dynamic DNS domains hosted behind mobile ISP connections.

Investigation

The investigation followed the malicious email, unpacked the embedded WinRAR self-extracting archive, and identified a VBS loader that launched a disguised AutoIt interpreter. The AutoIt script then decrypted and executed the Remcos implant, while the recovered configuration exposed the command-and-control domains, mutex value, and a persistence Run key. Researchers mapped the supporting infrastructure to three dynamic DNS domains and a rotating set of Nigerian IP addresses.

Mitigation

Organizations should block the identified dynamic DNS domains and associated IP ranges, monitor for the suspicious ipconfig /release and ipconfig /renew sequence, and detect AutoIt or VBS scripts spawning cmd.exe. Strong execution controls should also be applied to files using misleading double extensions, while registry Run entries such as WindowsUpdate should be monitored for abuse.

Response

If this activity is detected, isolate the affected endpoint immediately, terminate the Remcos process, remove the malicious Run key used for persistence, and perform a full forensic review for credential theft or follow-on activity. Detection content should also be updated to identify the network blackout technique and the specific filename patterns tied to the campaign.

"graph TB %% Class definitions classDef action fill:#99ccff classDef tool fill:#ffcc99 classDef malware fill:#ff9999 classDef data fill:#ccffcc %% Nodes email_phishing["Action – T1204.001 User Execution: Malicious Link Victim receives email with image containing a malicious MediaFire link."] class email_phishing action download_payload["Action – T1566.001 Phishing: Spearphishing Attachment Victim downloads WinRAR SFX executable masquerading as .pdf.scr."] class download_payload action file_double_ext["Action – T1036.007 Masquerading: Double File Extension File named invoice.pdf.scr hides a .scr executable."] class file_double_ext action script_vbs["Action – T1059.005 Command and Scripting Interpreter: Visual Basic VBS script (flvs.vbe) builds cmd.exe string and launches commands."] class script_vbs action tool_autoi["Tool – Name: AutoIt interpreter (renamed as .xls) Purpose: Executes malicious AutoIt script."] class tool_autoi tool script_autoi_obf["Action – T1059.010 Command and Scripting Interpreter: AutoIt/AutoHotKey Heavily obfuscated AutoIt script is executed."] class script_autoi_obf action obfusc_junk["Action – T1027.016 Obfuscated Files or Information: Junk Code Insertion Script contains 88u202fMB of meaningless comment blocks."] class obfusc_junk action obfusc_stripped["Action – T1027.008 Obfuscated Files or Information: Stripped Payloads Payload packed inside large filler data with custom hex encoding."] class obfusc_stripped action malware_remcos["Malware – Name: Remcos RAT Function: Remote access and control."] class malware_remcos malware c2_dns["Action – T1071.004 Application Layer Protocol: DNS Communicates with C2 servers via dynamicu2011DNS hostnames over encrypted TLS."] class c2_dns action persistence_autostart["Action – T1547.014 Boot or Logon Autostart Execution: Active Setup Creates HKCU\Software\Microsoft\Windows\CurrentVersion\Run\WindowsUpdate registry key."] class persistence_autostart action trusted_util["Action – T1127 Trusted Developer Utilities Proxy Execution Uses legitimate AutoIt interpreter as a trusted utility to run malicious code."] class trusted_util action deobfuscation["Action – T1140 Deobfuscate/Decode Files or Information Researchers decode custom hexu2011encoded PE and RC4u2011encrypted Remcos configuration."] class deobfuscation action %% Connections email_phishing –>|leads_to| download_payload download_payload –>|contains| file_double_ext file_double_ext –>|triggers| script_vbs script_vbs –>|loads| tool_autoi tool_autoi –>|executes| script_autoi_obf script_autoi_obf –>|includes| obfusc_junk script_autoi_obf –>|includes| obfusc_stripped script_autoi_obf –>|launches| malware_remcos malware_remcos –>|uses| c2_dns malware_remcos –>|establishes| persistence_autostart tool_autoi –>|used_as| trusted_util obfusc_junk –>|facilitates| deobfuscation obfusc_stripped –>|facilitates| deobfuscation "

Attack Flow

Attack Narrative & Commands:
1. Objective: Establish a C2 channel with the BlackToad Remcos implant using one of the known malicious DDNS domains on the hard‑coded port 50240.
2. Step‑by‑step:
  - Resolve the chosen malicious DDNS domain (pmitm.ddns.net).
  - Open a TCP socket to the resolved IP on port 50240.
  - Send a minimal “heartbeat” payload to emulate the implant’s initial handshake.
  - Keep the socket open for 30 seconds to ensure the firewall logs the outbound connection.
3. The outbound connection exactly matches the Sigma rule’s destination.ip list and destination.port criteria, producing a detectable firewall event.

Regression Test Script:

  # BlackToad C2 communication simulation (PowerShell)
  $c2Domain = "pmitm.ddns.net"      # one of the domains listed in the rule
  $c2Port   = 50240

  try {
      # Resolve domain to IP (adds DNS query telemetry)
      $ip = [System.Net.Dns]::GetHostAddresses($c2Domain) |
            Where-Object { $_.AddressFamily -eq 'InterNetwork' } |
            Select-Object -First 1

      if (-not $ip) { throw "Unable to resolve $c2Domain" }

      Write-Host "Resolved $c2Domain to $($ip.IPAddressToString). Connecting..."

      # Open TCP connection (generates firewall outbound log)
      $client = New-Object System.Net.Sockets.TcpClient
      $client.Connect($ip, $c2Port)

      # Send a simple heartbeat (hex 0x01)
      $stream = $client.GetStream()
      $payload = [byte[]](0x01)
      $stream.Write($payload, 0, $payload.Length)

      Write-Host "Heartbeat sent. Keeping connection alive for 30 seconds..."
      Start-Sleep -Seconds 30

      $stream.Close()
      $client.Close()
      Write-Host "Connection closed cleanly."
  }
  catch {
      Write-Error "Simulation failed: $_"
  }

Cleanup Commands:

  # Ensure any lingering sockets are closed
  Get-NetTCPConnection -RemotePort 50240 -State Established |
      ForEach-Object { Stop-Process -Id $_.OwningProcess -Force }
  # Optional: Flush DNS cache to remove the resolved DDNS entry
  ipconfig /flushdns
  Write-Host "Cleanup complete."

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