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3.29

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3/29/11&1&Borrowed from Brent ByungHoon Kang, GMU A Network of Compromised Computers on the Internet IP locations of the Waledac botnet. Borrowed from Brent ByungHoon Kang, GMU  Networks of compromised machines under the control of hacker, “bot-master”  Used for a variety of malicious purposes: • Sending Spam/Phishing Emails • Launching Denial of Service attacks • Hosting Servers (e.g., Malware download site) • Proxying Services (e.g., FastFlux network) • Information Harvesting (credit card, bank credentials, passwords, sensitive data.) Borrowed from Brent ByungHoon Kang, GMU After resolving the IP address for the IRC server, bot-infected machines CONNECT to the server, JOIN a channel, then wait for commands. Borrowed from Brent ByungHoon Kang, GMU The botmaster sends a command to the channel. This will tell the bots to perform an action. Borrowed from Brent ByungHoon Kang, GMU The IRC server sends (broadcasts) the message to bots listening on the channel. Borrowed from Brent ByungHoon Kang, GMU3/29/11&2&The bots perform the command. In this example: attacking / scanning CNN.COM. Borrowed from Brent ByungHoon Kang, GMU  Unfortunately, the detection, analysis and mitigation of botnets has proven to be quite challenging  Supported by a thriving underground economy ◦ Professional quality sophistication in creating malware codes ◦ Highly adaptive to existing mitigation efforts such as taking down of central control server. 8 Borrowed from Brent ByungHoon Kang, GMU  Traditional botnet communication ◦ Central IRC server for Command & Control (C&C) ◦ Single point of mitigation:  C&C Server can be taken down or blacklisted  Botnets with peer to peer C&C ◦ No single point of failure. ◦ E.g., Waldedac, Storm, and Nugache  Multi-layered Architecture to obfuscate and hide control servers in upper tiers. Borrowed from Brent ByungHoon Kang, GMU  Botmaster publishes commands under the key.  Bots are searching for this key periodically  Bots download the commands =>Asynchronous C&C Borrowed from Brent ByungHoon Kang, GMU  Each Supernode (server) publishes its location (IP address) under the key 1 and key 2  Subcontrollers search for key 1  Subnodes (workers) search for key 2 to open connection to the Supernodes => Synchronous C&C Borrowed from Brent ByungHoon Kang, GMU  Virus Scanner at Local Host ◦ Polymorphic binaries against signature scanning ◦ Not installed even though it is almost free ◦ Rootkit  Network Intrusion Detection Systems ◦ Keeping states for network flows ◦ Deep packet inspection is expensive ◦ Deployed at LAN, and not scalable to ISP-level ◦ Requires Well-Trained Net-Security SysAdmin Borrowed from Brent ByungHoon Kang, GMU3/29/11&3&13 Conficker infections are still increasing after one year!!! There are millions of computers on the Internet that do not have virus scanner nor IDS Borrowed from Brent ByungHoon Kang, GMU  Used for spam blocking, firewall configuration, DNS rewriting, and alerting sys-admins regarding local infections.  Fundamentally differs from existing Intrusion Detection System (IDS) approaches ◦ IDS protects local hosts within its perimeter (LAN) ◦ An enumerator would identify both local as well as remote infections  Identifying remote infections is crucial ◦ There are numerous computers on the Internet that are not under the protection of IDS-based systems. 14 Borrowed from Brent ByungHoon Kang, GMU  Need to know the method and protocols for how a bot communicates with its peers  Using sand-box technique ◦ Run bot binary in a controlled environment ◦ Network behaviors are captured/analyzed  Investigating the binary code itself ◦ Reversing the binary into high level codes ◦ C&C Protocol knowledge and operation details can be accurately obtained Borrowed from Brent ByungHoon Kang, GMU  Given network protocol knowledge, crawlers: 1. collect list of initial bootstrap peers into queue 2. choose a peer node from the queue 3. send to the node look-up or get-peer requests 4. add newly discovered peers to the queue 5. repeat 2-5 until no more peer to be contacted  Can’t enumerate a node behind NAT/Firewall  Would miss bot-infected hosts at home/office! Borrowed from Brent ByungHoon Kang, GMU  Given P2P protocol knowledge that bot uses  A collection of “routing-only” nodes that ◦ Act as peer in the P2P network, but ◦ Controlled by us, the defender  PPM nodes can observe the traffic from the peer infected hosts  PPM node can be contacted by the infected hosts behind NAT/Firewall Borrowed from Brent ByungHoon Kang, GMU Crawler PPM PPM PPM Borrowed from Brent ByungHoon Kang, GMU3/29/11&4&Borrowed from Brent ByungHoon Kang, GMU  DHCP  NATs  Non-uniform bot distribution  Churn  Most estimates put size of largest botnets at tens of millions of bots ◦ Actual size may be much smaller if we account for all of the above  Botnets use a lot of newly-created domains for phishing and malware delivery  Fast flux: changing name-to-IP mapping very quickly, using various IPs to thwart defense attempts to bring down botnet  Single-flux: changing name-to-IP mapping for individual machines, e.g., a Web server  Double-flux: changing name-to-IP mapping for DNS nameserver too  Proxies on compromised nodes fetch content from backend servers  Advantages for the attacker: ◦ Simplicity: only one back end server is needed to deliver content ◦ Layers of protection through disposable proxy nodes ◦ Very resilient to attempts for takedown  Look for domain names where mapping to IP changes often ◦ May be due to load balancing ◦ May have other (non-botnet) cause, e.g., adult content delivery ◦ Easy to fabricate domain names  Look for DNS records with short-lived domain names, with lots of A records, lots of NS records and diverse IP addresses (wrt AS and network access type)  Look for proxy nodes by poking them  They have been known to fight back ◦ DDoS IPs that poke them (even if low workers are scanned)  They have been known to fabricate data for honeynets ◦ Honeynet is a network of computers that sits in


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