Crypto Ransomware: Attack Methods and Mitigation Strategies

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The Crypto24 group is a cybercriminal organization that carries out ransomware attacks, encrypting victims’ data and demanding ransom payments. Below is a detailed breakdown of their operations and how to defend against them.

Activities

Crypto24 is known for:

• Encrypting victims’ data and demanding ransom payments.
• Threatening to leak stolen data if the ransom is unpaid.
• Recent attacks include breaches at CMC Corporation (April 12, 2025, compromising ~2 TB of data) and Taxplan (April 8, 2025).

Attack Methods

• File Encryption: Appends `.crypto24` to locked files (e.g., `1.jpg` → 1.jpg.crypto24).
• Infection Vectors:
• Phishing emails with malicious attachments.
• Malicious ads (malvertising).
• Exploiting unpatched software vulnerabilities.
• Ransom Notes: Leaves `Decryption.txt` with contact details (e.g., [email protected]).

Characteristics

• Operates as Ransomware-as-a-Service (RaaS), allowing low-skilled hackers to deploy attacks.
• Threatens to publish stolen data on dark web leak sites.
• No free decryption tools available—recovery without attackers’ key is nearly impossible.

Impact

Victims span technology, finance, and business services. Even “small-scale” attacks (like CMC’s) can disrupt operations by compromising sensitive data (tokens, websites).

You Should Know: How to Detect and Mitigate Crypto24 Attacks

1. Detect Ransomware Activity

• Linux Command to check for suspicious file extensions:

  find / -type f -name ".crypto24" 2>/dev/null
  

• Windows PowerShell to monitor unusual file changes:

  Get-ChildItem -Path C:\ -Recurse -Force -ErrorAction SilentlyContinue | Where-Object { $_.Extension -eq ".crypto24" }
  

2. Isolate Infected Systems

• Linux: Disconnect from network immediately:

  ifconfig eth0 down
  

• Windows: Disable network adapters via CMD:

  netsh interface set interface "Ethernet" admin=disable
  

3. Check for Ransom Notes

• Search for Decryption.txt:

  locate Decryption.txt
  

Or in Windows:

dir /s C:\Decryption.txt

4. Prevent Further Spread

• Block Known IoCs (Indicators of Compromise):

  iptables -A INPUT -s 185.165.29.0/24 -j DROP  Example Crypto24 C2 IP range
  

• Windows Firewall Rule:

  New-NetFirewallRule -DisplayName "Block Crypto24 C2" -Direction Outbound -Action Block -RemoteAddress 185.165.29.0/24
  

5. Restore from Backups

• Linux (rsync backup restore):

  rsync -avz /backup/ /original_data/
  

• Windows (Shadow Copy restore):

  vssadmin list shadows
  vssadmin restore shadow /shadow={ID}
  

6. Report the Attack

• Submit samples to VirusTotal:

  curl --request POST --url 'https://www.virustotal.com/vtapi/v2/file/scan' --form 'apikey=YOUR_API_KEY' --form 'file=@malicious_file'
  

What Undercode Say

Crypto24 exemplifies the growing threat of Ransomware-as-a-Service (RaaS), lowering the entry barrier for cybercriminals. Key takeaways:
– Never pay the ransom—funding attackers fuels more attacks.
– Air-gapped backups are critical for recovery.
– Patch management reduces exploit risks—use:

sudo apt update && sudo apt upgrade -y  Linux

Or Windows:

Install-Module PSWindowsUpdate -Force
Install-WindowsUpdate -AcceptAll -AutoReboot

– Network segmentation limits lateral movement.

Expected Output:

A hardened system with:

• Real-time file integrity monitoring (FIM):

  auditctl -w /etc/ -p wa -k critical_files
  

• Automated backups:

  tar -czvf /backup/$(date +%Y%m%d).tar.gz /critical_data
  

• Blocked malicious IPs via firewall rules.

Stay vigilant—ransomware evolves, but proactive defense minimizes damage.

References:

Reported By: Phuong Nguyen – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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