Blog | G5 Cyber Security

Bot Command & Control Channels: Blocking & Detection

G5 Cyber Security

TL;DR

This guide shows you how to identify and block channels used by botnets (groups of hacked computers controlled remotely). We’ll cover finding these channels, using tools to stop them communicating, and ways to prevent bots from infecting your systems in the first place.

Identifying Bot Command & Control Channels

  1. Network Traffic Analysis: Look for unusual communication patterns. Bots often talk to a small number of servers repeatedly.
    • High Volume Outbound Connections: A single computer sending lots of data out, especially at odd hours.
    • Connections to Unknown IPs/Domains: Use online tools (like VirusTotal or WHOIS) to check if the server is known for malicious activity.
    • Unusual Ports: Bots might use non-standard ports to avoid detection.
  2. Log Analysis: Check your firewall, web server, and intrusion detection system logs.
    • Repeated Failed Login Attempts: A sign someone is trying to brute-force their way in.
    • Suspicious User Agent Strings: Bots often use generic or unusual user agent strings. Look for patterns in your web server access logs.
    • Malware Signatures: Your security software might already be flagging bot activity.
  3. DNS Queries: Monitor DNS requests.
    • Fast-Flux DNS: A technique where the IP address associated with a domain changes rapidly, making it hard to track down the server.
    • Domain Generation Algorithms (DGAs): Bots create random domain names to find their command & control servers. Tools can help identify these patterns.

Blocking Bot Command & Control Channels

  1. Firewall Rules: Block communication with known malicious IPs and domains.
    • IP Blocking: Add the IP addresses to your firewall’s block list. 
      iptables -A INPUT -s [IP Address] -j DROP
    • Domain Blocking: Block access to the malicious domain names. Many firewalls allow you to block domains directly.
  2. DNS Sinkholing: Redirect DNS requests for malicious domains to a harmless server.
    • This prevents bots from reaching their command & control servers. Requires configuring your DNS server or using a third-party sinkhole service.
  3. Web Application Firewall (WAF): Protect your web applications from bot attacks.
    • WAFs can identify and block malicious requests before they reach your server.

Preventing Bot Infections

  1. Keep Software Updated: Regularly update your operating system, web server, and all other software.
    • Updates often include security patches that fix vulnerabilities bots can exploit.
  2. Strong Passwords & Multi-Factor Authentication (MFA): Use strong, unique passwords for all accounts and enable MFA whenever possible.
    • This makes it harder for attackers to gain access to your systems.
  3. Antivirus/Anti-Malware Software: Install and keep up-to-date antivirus and anti-malware software.
    • These tools can detect and remove bots from your systems.
  4. Network Segmentation: Separate your network into smaller segments to limit the spread of infections.
    • If one segment is compromised, it won’t necessarily affect the entire network.
  5. Regular Security Audits & Penetration Testing: Identify and fix vulnerabilities before attackers can exploit them.

Resources

Exit mobile version