Flame Trojan C&C Domains

TL;DR

This guide helps identify and block Command & Control (C&C) domains used by the Flame/Skywiper trojan. It covers domain lists, DNS analysis techniques, and blocking methods.

Identifying Flame C&C Domains

1. Understand Domain Lists: Several sources maintain lists of known Flame-related domains. These are a good starting point. Some key resources include:
• MalwareBazaar: https://mbazaar.abuse.ch/browsing/domains?query=flame
• Threat intelligence feeds (commercial or open-source).
2. Historical DNS Data: Flame used a complex network of domains, many of which are no longer active. Examining historical DNS records can reveal previously used C&C servers.
   • Passive DNS Services: Use services like VirusTotal or SecurityTrails to query domain history.
   • Example using dig (Linux/macOS):

     dig +trace flame-domain.com

     This shows the DNS resolution path over time, potentially revealing older servers.

3. Domain Registration Information: Look for patterns in domain registration data.
   • WHOIS Lookup: Use a WHOIS tool (e.g., https://whois.domaintools.com/) to check the registrant, creation date, and other details.
   • Flame operators often used privacy-protected registrations or fake contact information. Domains registered around the same time with similar patterns are suspicious.

DNS Analysis Techniques

1. Reverse DNS Lookups: Identify domains associated with specific IP addresses.
   • Use tools like host (Linux/macOS) or online reverse DNS lookup services.
   • Example using host:

     host 192.0.2.1

     This will show the domain name(s) associated with that IP address, if any.

2. DNS Zone Transfers (AXFR): Attempt to perform a zone transfer on potentially compromised DNS servers.
   • This is often disabled but can reveal all records for a domain.
   • Use dig with the AXFR option:

     dig +trace flame-domain.com axfr

     (Requires permission and is rarely successful).

3. DNS Record Types: Analyse different DNS record types (A, CNAME, MX, TXT) for anomalies.
   • Look for unusual CNAME records pointing to suspicious domains.
   • Check TXT records for potential malware-related strings or configuration data.

Blocking Flame C&C Domains

1. Firewall Rules: Add rules to your firewall to block communication with known and suspected C&C domains.
   • Most firewalls allow you to create rules based on domain names.
   • Example (iptables – Linux):

     iptables -A OUTPUT -d flame-domain.com -j DROP

     (Replace ‘flame-domain.com’ with the actual domain).

2. DNS Sinkholes: Redirect DNS queries for malicious domains to a sinkhole server.
   • This prevents infected machines from reaching the C&C servers.
   • Configure your DNS server (e.g., BIND, Unbound) to forward queries for blocked domains to the sinkhole IP address.
3. Web Proxy Filters: Block access to malicious domains through your web proxy.
   • Most web proxies allow you to create blocklists based on domain names or URLs.
4. Threat Intelligence Platform Integration: Integrate domain lists into your threat intelligence platform (TIP) for automated blocking and alerting.

Important Considerations

• Flame is an old trojan, but its techniques are still relevant.
• C&C domains change frequently; keep your blocklists updated.
• False positives can occur; carefully review any blocked traffic before implementing permanent blocks.
• Combine domain blocking with other security measures (e.g., endpoint detection and response, intrusion prevention systems) for comprehensive protection against cyber security threats.