Fake CAPTCHA Scams: How Cybercriminals Trick Users into Running Malicious Code

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Cybercriminals are increasingly using fake CAPTCHA verification pages to deceive users into executing malicious code. A recent campaign, known as SmartApeSG, injects fraudulent Cloudflare Turnstile-like prompts into compromised websites. These fake CAPTCHAs instruct users to copy and paste malicious commands, leading to malware infections.

How the Attack Works:

  1. Compromised Legitimate Sites: Attackers hack websites and insert malicious scripts.
  2. Fake CAPTCHA Users see a fake Cloudflare Turnstile or CAPTCHA verification.
  3. Clipboard Injection: The script copies malicious commands to the clipboard.
  4. User Execution: Victims paste and run the code, infecting their systems.

Example of a Malicious Domain:

  • bnpparibas[.]top (fake BNP Paribas site)

You Should Know:

How to Detect Fake CAPTCHA Scams

  1. Check the URL: Verify if the domain matches the legitimate service (e.g., cloudflare.com).
  2. Inspect Browser Console: Press `F12` (DevTools) and check for suspicious scripts.
  3. Avoid Pasting Random Commands: Never execute unknown code from untrusted sources.

Linux Commands to Investigate Suspicious Websites

 Check DNS records of a suspicious domain 
dig A bnpparibas.top

Analyze network traffic with tcpdump 
sudo tcpdump -i eth0 host bnpparibas.top -w traffic.pcap

Use curl to inspect HTTP headers 
curl -I http://bnpparibas.top

Check for malware with ClamAV 
sudo clamscan -r ~/Downloads

Windows Commands to Detect Malicious Activity

 Check active network connections 
netstat -ano | findstr "ESTABLISHED"

Scan for suspicious processes 
tasklist /svc | findstr "unknown"

Analyze PowerShell logs 
Get-WinEvent -LogName "Microsoft-Windows-PowerShell/Operational" | Select-Object -First 10

Mitigation Steps

1. Use Browser Extensions:

  • uBlock Origin (blocks malicious scripts)
  • NoScript (disables unauthorized JavaScript)
  1. Enable Clipboard Alerts: Some security tools warn when scripts modify clipboard content.
  2. Educate Users: Train employees/teams to recognize fake verification prompts.

What Undercode Say

Fake CAPTCHA scams exploit human trust in security checks. Attackers leverage browser APIs to manipulate clipboards, making detection harder. Always verify unusual prompts before executing commands.

Expected Output:

  • Malicious domains logged in firewall/IDS.
  • Suspicious PowerShell or Bash commands flagged.
  • Users avoiding fake CAPTCHA scams.

Prediction

As CAPTCHA bypass tools improve, attackers will refine fake verification scams, possibly using AI-generated prompts. Organizations must adopt zero-trust browsing policies to combat this threat.

(Relevant article: How Hackers Exploit Fake CAPTCHAs)

IT/Security Reporter URL:

Reported By: Jeromesegura Reminder – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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