WhatsApp Weaponized: How a Single VBS Attachment Unleashes Cloud Payloads and MSI Backdoors – A Technical Deep Dive + Video

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Introduction:

A new, highly evasive malware campaign is weaponizing WhatsApp messages to deliver malicious Visual Basic Script (VBS) files that, once executed on Windows, deploy a multi-stage attack chain. By abusing legitimate built‑in tools (LOLBins) like `curl.exe` and bitsadmin.exe, the attacker creates hidden folders, renames binaries to appear innocuous (e.g., netapi.dll, sc.exe), and ultimately installs an unsigned MSI backdoor for persistent remote access. This article dissects the technical anatomy of the attack, provides step‑by‑step analysis commands, and offers actionable detection and hardening strategies.

Learning Objectives:

  • Understand the complete infection chain – from a deceptive WhatsApp message to backdoor persistence.
  • Analyze how attackers use file renaming and LOLBins to evade signature‑based detection.
  • Implement Windows‑specific detection, containment, and mitigation measures against VBS‑driven, cloud‑delivered payloads.

You Should Know

1. Initial Infection Vector: WhatsApp VBS Attachment Analysis

The attack begins with a WhatsApp message carrying a `.vbs` attachment. When the user opens it, Windows Script Host executes the script silently. To analyze a suspicious VBS file safely, use a sandbox or a dedicated analysis VM. Below are commands to inspect the script’s content without running it.

Windows (PowerShell) – Extract and view VBS content:

 List hidden VBS files in Downloads
Get-ChildItem -Path "$env:USERPROFILE\Downloads" -Filter .vbs -Force

View the content (replace 'malicious.vbs' with actual filename)
Get-Content -Path "$env:USERPROFILE\Downloads\malicious.vbs"

Linux (if VBS file is transferred) – Use `strings` and file:

strings malicious.vbs | head -50
file malicious.vbs

Step‑by‑step guide to safely analyse the VBS:

  1. Isolate the host from the network (disable Wi‑Fi/ Ethernet).
  2. Copy the VBS file to a non‑executable location (e.g., C:\Analysis\).
  3. Open the script in Notepad or VS Code – look for CreateObject, WScript.Shell, Run, cmd.exe, mkdir, copy, curl, bitsadmin.

4. Use PowerShell to extract obfuscated strings:

`(Get-Content .\malicious.vbs) -replace ‘&h’,’0x’ | Out-String`

5. Search for URLs or IPs using regex:

`Select-String -Path .\malicious.vbs -Pattern ‘\b(https?|ftp)://\S+’`

  1. LOLBin Abuse & File Masquerading – Detecting Renamed Binaries

After execution, the VBS script creates hidden folders under `C:\ProgramData` (e.g., C:\ProgramData\Microsoft\Drivers\) and copies legitimate Windows tools, renaming them to misleading names like `netapi.dll` and sc.exe. The original PE metadata (e.g., OriginalFileName) still reveals their true identity.

Windows – Find renamed `curl.exe` or `bitsadmin.exe`:

 Search for any file in ProgramData that has OriginalFileName = "curl.exe"
Get-ChildItem -Path C:\ProgramData -Recurse -ErrorAction SilentlyContinue | ForEach-Object {
$sig = Get-AuthenticodeSignature -FilePath $<em>.FullName -ErrorAction SilentlyContinue
if ($sig.SignerCertificate -eq $null -and $</em>.Extension -ne '.ps1') {
$ver = [System.Diagnostics.FileVersionInfo]::GetVersionInfo($<em>.FullName)
if ($ver.OriginalFilename -eq 'curl.exe' -or $ver.OriginalFilename -eq 'bitsadmin.exe') {
Write-Host "Suspicious: $</em> -> OriginalFilename: $($ver.OriginalFilename)"
}
}
}

Using Sysinternals Sigcheck (more reliable):

sigcheck64.exe -a C:\ProgramData\ /s /c | findstr /i "curl.exe bitsadmin.exe"

Step‑by‑step detection of masqueraded binaries:

  1. List all hidden folders in C:\ProgramData: `dir /ah C:\ProgramData`
    2. For each suspicious `.exe` or .dll, run `sigcheck -a -q ` to view OriginalFileName.
  2. Compare the hash with known good files: `Get-FileHash ` vs official Microsoft binaries.
  3. Monitor process creation events (Event ID 4688) for parent process `wscript.exe` or `cscript.exe` spawning curl, bitsadmin, or msiexec.

  4. Cloud Payload Delivery – Network & API Security Analysis

The attack uses renamed `curl.exe` or `bitsadmin.exe` to download next‑stage payloads from legitimate cloud storage (e.g., Dropbox, Google Drive, OneDrive). This bypasses many web filters because the traffic goes to trusted domains.

Windows – Monitor outgoing connections from suspicious processes:

 Real-time network connections for processes under ProgramData
netstat -ano | findstr ESTABLISHED
Get-NetTCPConnection | Where-Object {$_.OwningProcess -in (Get-Process -Name curl,bitsadmin).Id}

Step‑by‑step network analysis using `tcpview` (Sysinternals):

1. Download and run `tcpview.exe`.

  1. Filter by process name (e.g., `netapi.dll` – which is actually curl).
  2. Look for connections to cloud storage IP ranges (list AWS, Azure, Google Cloud prefixes).
  3. Capture a PCAP with `netsh trace start capture=yes` or Wireshark – filter http.request or ssl.handshake.

API security considerations:

Attackers often abuse unauthenticated cloud storage URLs (e.g., `https://api.dropboxapi.com/2/files/download`). To defend:
– Use SSL inspection to examine cloud API calls.
– Implement allow‑listing of corporate‑approved cloud tenants.
– Monitor for anomalous `curl` user‑agents or `bitsadmin` jobs via Sysmon Event ID 3 (network connection).

4. Unsigned MSI Backdoor – Extraction and Mitigation

The final stage is an unsigned MSI installer that installs a persistent backdoor. Attackers often sign MSI files with self‑signed or stolen certificates to bypass basic checks.

Extract MSI contents without executing:

msiexec /a malicious.msi TARGETDIR=C:\MSIExtract /qb

or use `lessmsi` (open‑source):

lessmsi x malicious.msi C:\MSIOut

Analyze MSI custom actions (often contain malicious scripts):

 Using Orca (Windows SDK) – open MSI and inspect 'CustomAction' table
orca.exe malicious.msi

PowerShell to list custom actions
$msi = Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like "backdoor"}
 Alternative: use MSI API via COM
$installer = New-Object -ComObject WindowsInstaller.Installer
$database = $installer.OpenDatabase("malicious.msi", 0)
$view = $database.ExecuteView("SELECT  FROM CustomAction")
$record = $view.Fetch()
while($record -ne $null) {
Write-Host "Action: $($record.StringData(1)) Type: $($record.StringData(2))"
$record = $view.Fetch()
}

Mitigation – Block unsigned MSI via Group Policy:

  • Computer Configuration → Windows Settings → Security Settings → Software Restriction Policies – create a rule to disallow `.msi` from `%TEMP%` and C:\ProgramData.
  • Enable Windows Defender Application Control (WDAC) – only allow MSI files signed by trusted publishers.
  • PowerShell to block MSI execution:

`Set-ItemProperty -Path “HKLM:\SOFTWARE\Policies\Microsoft\Windows\Installer” -Name “DisableMSI” -Value 2`

5. Persistence Mechanisms – Finding Hidden Artifacts

The VBS script creates hidden folders and may install scheduled tasks or run keys to survive reboot.

Windows commands to uncover persistence:

 List hidden directories in ProgramData
dir /ah C:\ProgramData

Check Run/RunOnce keys
reg query HKCU\Software\Microsoft\Windows\CurrentVersion\Run
reg query HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

List scheduled tasks created by non‑admin users
schtasks /query /fo LIST /v | findstr /i "task to run"

Autoruns (Sysinternals) – comprehensive
autoruns64.exe -a -c -v > autoruns.csv

Step‑by‑step eradication:

  1. Stop processes associated with renamed binaries using taskkill /F /IM <processname>.
  2. Delete the hidden folder: `rmdir /s /q “C:\ProgramData\Microsoft\Drivers”` (adjust path).
  3. Remove registry entries pointing to the dropped MSI backdoor.
  4. Delete scheduled tasks: schtasks /delete /tn "MaliciousTaskName" /f.

  5. Detection & Response – YARA and EDR Rules

Create YARA rules to detect VBS scripts that invoke LOLBins and create hidden directories.

Example YARA rule for VBS hunting:

rule WhatsApp_VBS_LOLBin {
meta:
description = "Detects VBS scripts using curl or bitsadmin with hidden directory creation"
author = "Undercode"
date = "2026-04-02"
strings:
$vbs1 = "CreateObject(\"WScript.Shell\")" nocase
$vbs2 = "Run \"cmd.exe /c mkdir" nocase
$vbs3 = "ProgramData" nocase
$vbs4 = "curl.exe" nocase
$vbs5 = "bitsadmin.exe" nocase
condition:
$vbs1 and ($vbs2 or $vbs3) and ($vbs4 or $vbs5)
}

EDR hunting query (Microsoft 365 Defender):

DeviceProcessEvents
| where FolderPath contains "\ProgramData\"
| where ProcessCommandLine contains "curl" or ProcessCommandLine contains "bitsadmin"
| where InitiatingProcessFileName in~ ("wscript.exe", "cscript.exe")

7. Hardening Against Messaging‑Based Attacks

Prevention is better than detection. Apply these hardening steps to reduce attack surface.

Windows – Disable VBS script execution via Group Policy:
– Computer Configuration → Administrative Templates → Windows Components → Windows Script Host → Set “Turn off Windows Script Host” to Enabled.
– Alternatively, restrict `.vbs` association: `ftype VBSFile=”%SystemRoot%\System32\notepad.exe” “%1″`

Block unsigned MSI installers via AppLocker:

 Create a default rule to allow only signed MSI from Program Files
New-AppLockerPolicy -RuleType Msi -User Everyone -Action Allow -Path "%PROGRAMFILES%\" -Service "TrustedInstaller"
Set-AppLockerPolicy -Policy $policy -Merge

Cloud hardening:

  • Use CASB (Cloud Access Security Broker) to block downloads from consumer cloud storage (Dropbox, Google Drive) unless explicitly authorized.
  • Implement TLS inspection and enforce corporate proxy with authentication.

What Undercode Say

  • Key Takeaway 1: Attackers increasingly rely on social‑engineering via messaging apps (WhatsApp) combined with fileless‑like techniques using native Windows tools. The renaming of `curl.exe` to `netapi.dll` demonstrates how simple obfuscation defeats signature‑based AV.
  • Key Takeaway 2: Detection must shift from hash‑based to behaviour‑based – monitoring parent‑child process relationships (e.g., `wscript.exe` spawning curl) and file system events under `C:\ProgramData` is critical.
  • Key Takeaway 3: Cloud APIs are the new command‑and‑control. Organisations should treat all traffic to cloud storage as suspicious unless accompanied by corporate authentication tokens. Implementing allow‑lists for approved cloud tenants reduces risk.
  • Analysis: The attack chain’s elegance lies in its use of legitimate binaries (LOLBins) and trusted cloud domains, bypassing both network firewalls and endpoint signatures. The VBS script acts as a tiny stager – less than 10 KB – making it easy to distribute. Defenders must prioritise script host restrictions (disable VBS unless absolutely needed) and enforce application control for MSI files. The unsolicited nature of WhatsApp messages also calls for user awareness training: never open unexpected attachments, even from known contacts (account compromise is common).

Prediction

In the next 12 months, we will see a surge in “chain‑loading” attacks that weaponise multiple messaging platforms (Telegram, Signal, Discord) with AI‑generated lure messages that are nearly indistinguishable from legitimate communication. Attackers will move beyond VBS to JScript, HTA, and even Office macros that invoke cloud CLI tools (e.g., AWS CLI, Azure CLI) to download payloads, complicating detection. Organisations that fail to adopt Zero Trust principles – especially application allow‑listing and script execution controls – will face repeated compromises. The only long‑term mitigation is to treat every attachment as a potential exploit and enforce execution policies that assume breach before execution.

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Reported By: Mayura Kathiresh – Hackers Feeds
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