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Botnets

Botnets. Abhishek Debchoudhury Jason Holmes. What is a botnet?. A network of computers running software that runs autonomously. In a security context we are interested in botnets in which the computers have been compromised and are under the control of a malicious adversary.  .

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Botnets

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  1. Botnets Abhishek Debchoudhury Jason Holmes

  2. What is a botnet? A network of computers running software that runs autonomously. In a security context we are interested in botnets in which the computers have been compromised and are under the control of a malicious adversary. 

  3. What are botnets used for? • Spam • ~85% of email is spam • DDoS attacks • Identity theft • Cost in 2006: $15.6 billion • Phishing attacks • 4500 active sites at any given time, 1 million previously active sites

  4. What are botnets used for? • Hosting pirated software • Hosting and distributing malware • Click fraud • ~14% of all advertisement clicks are fraudulent • Packet sniffing

  5. What's a botmaster? • Person(s) controlling the botnet • Business person • Often paid by customers • Willing to rent out botnet • Glory Hound • Brags about size of botnet • Willing to talk to researchers • Script kiddies • Inexperienced

  6. Command Topologies • Star • Bots tied to centralized C&C server. • Multi-Server  • Same as star but with multiple C&C servers  • Hierarchical • Parent bot control child bots • Random • Full P2P support

  7. Topology Tradeoffs Control vs. Survivability • More Control  •     Easier to get botnet to do your bidding •     Easier to shut down • Survivability •     Harder to shut down •     Less control

  8. Communication Methods • HTTP • Easy for attacker to blend in • IRC •  Harder to hide since IRC is much less used than HTTP • Custom • Makes use of new application protocols

  9. Propagation Methods • Scanning • 0-day attacks • Worm-like behavior • Infected e-mail attachments • Drive-by-downloads • Trojan horses

  10. Infection Procedure

  11. History and Notable Botnets • 1999 - Sub7 • 2000 - GTbot a bot based on mIRC  • 2002 - SDbot small c++ binary with widely available source code • 2002 - Agobot staged attacked with modular payload • 2003 - Sinit first peer-to-peer botnet  • 2004 - Bagle and Bobax first spamming botnets • 2007 - Storm botnet  • 2009 - Waledac botnet • 2009 - Zeus botnet

  12. Defense Three main issues: •   How to find them  •   Decide how to fight them (defense vs offense) •   How to negate the threat

  13. Detection: Analyze Network Traffic • Temporal • Same repeated traffic pattern from node • Spatial • Nodes in same subnet likely infected

  14. Detection: Packet Analysis • Using statistical analysis on network traffic flows • Classify packets based on payload signature and destination port • Looking for clusters of similar data packets  •  n-gram byte distribution • IRC botnet traffic it is not very diverse compared to traffic generated by humans

  15. Strategy Active: attack the source • Shut down C&C server • Re-route DNS • Pushback Passive: defend at the target • Filters • Human attestation • Collective defense

  16. Defense - Change DNS routing Defender figures out domain that attacker is using and takes control Pros: • Central point of attack • Severs botmaster's ability to communicate with the botnet Cons: •  Not all bot nets have C&C server •  C&C domain changes often • > 97% turn over per week

  17. Defense -Black Lists Defender creates list of attackers. Used primarily as spam fighting technique Pros: •  Allows for broad knowledge sharing •  Easy to maintain/understand Cons:  •  List has to be continually updated •  Innocent service providers get blocked

  18. Defense -Human Attestation Defender requests that client prove his humanity. • Requires the client to have a trusted attester • Accomplished through the use of a Trusted Platform Module • Several methods for an attester to determine that the actions were initiated by  a human • Through the use of secure input devices which cryptographically sign their output • CAPTCHA or secure prompt • Analyze keystrokes and mouse movement

  19. Defense - Collective defense We must all hang together or assuredly we shall all hang separately.                             -- Benjamin Franklin •  Key contentions  • Most end users don't know/care about security • The best way to secure the internet is through a collective effort without relying on end users • Compromised hardware must be quarantined until healthy • Authenticate healthiness before network access • Public Health Model for Internet • Allow everyone but identify suspicious behavior • Japan's Cyber Clean Center • Finnish national Computer Emergency Response Team

  20. Thanks

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