How to Defend Against NCSC-Flagged Social Engineering Attacks on Signal and WhatsApp

The UK's National Cyber Security Centre (NCSC) recently issued a critical security alert highlighting a surge in cyber-attacks targeting messaging platforms like WhatsApp and Signal. These attacks specifically focus on “high-risk” individuals—such as journalists, lawyers, and politicians—utilizing sophisticated social engineering tactics to compromise accounts and devices.

For managed security service providers (MSSPs) and internal security teams, this alert underscores a vital shift: the perimeter is no longer just the network firewall; it is now the user's endpoint and their communication habits. This post analyzes the threat landscape and provides defensive strategies and detection logic to protect your organization's most valuable assets.

Technical Analysis

While the NCSC alert focuses on social engineering, the technical impact often leads to Account Takeover (ATO) or, in more severe cases, the deployment of commercial surveillance spyware (often referred to as “stalkerware”).

The Attack Vector: Attackers are exploiting the trust users place in encrypted messaging. The primary techniques include:

1. Number Switching Attacks: Attackers pose as the target, claiming to have lost their phone or SIM card, and convince contacts to re-register the target's phone number on a new device controlled by the attacker.
2. Malicious Link Distribution (Smishing): Phishing links sent via Signal or WhatsApp designed to harvest credentials or deliver malware.
3. “Zero-Click” Exploits (High Severity): In targeted cases, attackers may exploit vulnerabilities in the handling of incoming packets (e.g., malformed VoIP calls) to inject spyware without user interaction.

Affected Systems:

• Mobile platforms (Android, iOS).
• Desktop applications for Signal and WhatsApp (Windows, macOS, Linux).

Severity: High. Successful compromise of a VIP's messaging app can lead to data exfiltration, source code disclosure, or geopolitical intelligence gathering.

Patch/Remediation Status: There is no single “patch” for social engineering. However, maintaining the latest version of messaging applications is critical to mitigate buffer overflow and memory corruption vulnerabilities used in zero-click exploits. Organizations must enforce application updates and configure privacy settings to restrict account takeover.

Defensive Monitoring

Detecting social engineering is challenging, but defenders can monitor for anomalous behaviors on endpoints associated with these applications. Below are detection rules and hunts designed to identify potential compromise or malicious activity originating from messaging platforms.

SIGMA Rules

These rules monitor for suspicious child processes spawned by messaging applications or the presence of phishing artifacts.

---
title: Suspicious Child Process of Messaging Application
id: 9b3a1c4d-5e6f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects suspicious processes (e.g., PowerShell, CMD) spawned by Signal or WhatsApp desktop clients. This may indicate exploitation or malicious script execution.
references:
  - https://www.ncsc.gov.uk/news/organisations-urged-to-protect-their-data-from-spyware
author: Security Arsenal
date: 2023/10/24
tags:
  - attack.initial_access
  - attack.t1566.001
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|contains:
      - '\WhatsApp.exe'
      - '\Signal.exe'
    Image|endswith:
      - '\powershell.exe'
      - '\cmd.exe'
      - '\wscript.exe'
      - '\cscript.exe'
      - '\mshta.exe'
  condition: selection
falsepositives:
  - Legitimate administration tasks initiated by the user (rare)
level: high
---
title: Suspicious LNK File in User Downloads
id: a1b2c3d4-e5f6-4a5b-8c9d-0e1f2a3b4c5e
status: experimental
description: Detects the creation of .lnk files in the user Downloads folder. LNK files are frequently used in phishing campaigns to deliver malicious payloads.
references:
  - https://attack.mitre.org/techniques/T1566/001/
author: Security Arsenal
date: 2023/10/24
tags:
  - attack.initial_access
  - attack.t1566.001
  - attack.user_execution
  - attack.t1204.002
logsource:
  category: file_event
  product: windows
detection:
  selection:
    TargetFilename|contains: '\Downloads\'
    TargetFilename|endswith: '.lnk'
  condition: selection
falsepositives:
  - User manually creating shortcuts
level: medium

KQL (Microsoft Sentinel / Defender)

Use these queries to hunt for suspicious process chains involving Signal or WhatsApp, or to verify patch compliance.

// Detect suspicious child processes spawned by Signal or WhatsApp
DeviceProcessEvents
| where InitiatingProcessFileName in~ ('WhatsApp.exe', 'Signal.exe')
| where ProcessFileName in~ ('powershell.exe', 'cmd.exe', 'wscript.exe', 'regsvr32.exe', 'rundll32.exe')
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, ProcessFileName, ProcessCommandLine, FolderPath
| order by Timestamp desc


// Check for outdated versions of Signal/WhatsApp (Vulnerability Management)
DeviceRegistryEvents
| where RegistryKey contains @"\WhatsApp" or RegistryKey contains @"\Signal"
| where RegistryKey contains "DisplayVersion"
| project Timestamp, DeviceName, RegistryKey, RegistryValueData, PreviousRegistryValueData
| order by Timestamp desc

Velociraptor VQL

Velociraptor hunts for artifacts on the disk that may indicate a phishing attack or malware staging.

-- Hunt for suspicious file extensions in Downloads folders
SELECT FullPath, Size, Mtime, Atime
FROM glob(globs='/*/*/Downloads/*.lnk')
  OR glob(globs='/*/*/Downloads/*.exe')
  OR glob(globs='/*/*/Downloads/*.scr')
WHERE Mtime > now() - 7d

-- Hunt for Signal/WhatsApp config directories modified recently (Persistence checks)
SELECT FullPath, Size, Mtime, Mode
FROM glob(globs='/%AppData%/Signal/**')
  OR glob(globs='/%AppData%/WhatsApp/**')
WHERE Mtime > now() - 24h

PowerShell

This script helps administrators audit registry settings and recent file modifications in user directories that could signify a breach.

# Audit recent downloads for high-risk file types
$TimeThreshold = (Get-Date).AddDays(-7)
$Users = Get-ChildItem "C:\Users"

foreach ($User in $Users) {
    $DownloadsPath = Join-Path -Path $User.FullName -ChildPath "Downloads"
    if (Test-Path $DownloadsPath) {
        Write-Host "Checking $($User.Name)..." -ForegroundColor Cyan
        Get-ChildItem -Path $DownloadsPath -Recurse -Include *.lnk, *.exe, *.jar, *.vbs, *.js |
        Where-Object { $_.LastWriteTime -gt $TimeThreshold } |
        Select-Object FullName, LastWriteTime, Length
    }
}

Remediation

To protect your organization against these specific threats, implement the following controls immediately:

1. Enable Registration Locks:

   • Signal: Enable "Registration Lock" in Settings > Account. This requires the user's PIN to re-register the phone number on a new device, thwarting SIM-swap attacks.
   • WhatsApp: Enable "Two-Step Verification" in Settings > Account.

2. Configure Desktop Link Settings:

   • Disable or restrict the ability to link new devices to the corporate account unless physically verified.
   • In Signal, verify the "Safety Number" of contacts before sharing sensitive data.

3. Application Hardening:

   • Ensure all mobile devices (MDM) are configured to auto-update applications.
   • Disable installation of apps from untrusted sources (sideloading) on corporate devices.

4. User Awareness Training:

   • Explicitly train high-risk users on the "Number Switch" social engineering attack. Verify the identity of anyone asking for a code or claiming to have a new number via a secondary channel (e.g., phone call vs. text).

5. Network Segmentation:

   • Where possible, isolate high-risk user devices from critical development and production networks to limit the blast radius of potential spyware.

Related Resources

Security Arsenal Managed SOC Services AlertMonitor Platform Book a SOC Assessment soc-mdr Intel Hub