Flame Trojan C&C Domains

G5 Cyber Security

2 weeks ago

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

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).

Historical DNS Data: Flame used a complex network of domains, many of which are no longer active.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.

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

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.
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).
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

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).
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.
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.
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.