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Measurements and Mitigation of Peer-to-peer Botnets: A Case Study on Storm Worm

Measurements and Mitigation of Peer-to-peer Botnets: A Case Study on Storm Worm Thorsten Holz, Moritz Steiner, Frederic Dahl, Ernst Biersack, Felix Freiling. What is a botnet?. A bot is a hacked computer with some remote control mechanism A botnet is a network of these machines.

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Measurements and Mitigation of Peer-to-peer Botnets: A Case Study on Storm Worm

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  1. Measurements and Mitigation of Peer-to-peer Botnets: A Case Study on Storm Worm Thorsten Holz, Moritz Steiner, Frederic Dahl, Ernst Biersack, Felix Freiling

  2. What is a botnet? • A bot is a hacked computer with some remote control mechanism • A botnet is a network of these machines. • Typically under the control of one person or group.

  3. How are they used? • Spam • DDOS • Phishing

  4. How are machines compromised? • Worms • Trojans (Storm)‏ • Links to malicious sites (Storm)‏

  5. Tracking Botnets • Best technique is to use honeypots • A bot must contain information on how to bootstrap itself within the botnet. • Obtain information on how to connect • Craft a special client to do so

  6. Botnet Control Mechanisms • IRC • HTTP • A custom method • P2P (the latest and greatest)‏

  7. Storm Botnet • Propagates solely through email • Named from the Kyrill Storm in Europe • At one point, responsible for ~10% of all spam • Changes social engineering theme in emails frequently • P2P

  8. Storm Botnet, cont. • Very sophisticated binary packer • Rootkit • Time synchronized with NTP

  9. P2P Botnets • Storm botnet uses P2P. • Publish/subscribe style of communication • Unauthenticated

  10. Publish/Subscribe • Information is not directly sent • An information provider publishes a piece of information, i, by using an identifier that is derived solely from i. • A consumer can subscribe to that information by using a filter on the identifiers • The identifiers are usually derived from specific content or a hash function • The P2P system matches the published items to the subscriptions and delivers the information

  11. Storm P2P Scheme • Uses the Overnet DHT (Distributed Hash Table) Routing Protocol • Also starting to use Stormnet, which is encrypted by XORing with a 40-byte key. • Still unauthenticated • Each client generates a 128-bit ID

  12. Routing Lookup • Uses prefix matching • Node a forwards a query to a node d in its routing table that has the smallest XOR distance with d. • XOR distance is done on the DHT ids • A peer stores more contacts that are closer

  13. Routing Query • Done iteratively. • A node sends route requests to 3 peers, and they may or may not return peers that are even closer to the DHT ID. • These closer peers are then queried in the same manner.

  14. Publishing in Depth • Uses a key to identify and retrieve information • To deal with node churn, a key is published on 20 peers and is periodically republished. • Infected machines search for keys that the controller publishes.

  15. Storm Communication • To find other Storm machines, a bot subscribes to a key based off the function of the current day and a random number between 0 and 31. • f(d, r) = key

  16. Storm Publish Method • On Overnet, the Storm bots publish information in the following format: *.mpg;size=*

  17. Infiltrating a botnet • Can be dangerous • Craft a special P2P client • Goal is to defeat the control structure

  18. Crawling the Botnet • After building a custom P2P client, they can crawl the botnet by using a BFS. • Issue route requests to find all the peers. • Takes 20 to 40 seconds.

  19. Spying on the Botnet • Use a Sybil attack. • Introduce malicious peers to the botnet to gain control of parts or all of the network • Can monitor traffic or reroute requests to the wrong peers

  20. Mitigation • When the attack wants to issue a command, he publishes the information on the network • Because the information is unauthenticated, any member of the p2p network can publish information • From this, we can publish our own information to try to disrupt the communication channel

  21. Eclipse Attack • Position sybils closely around a keyword K. • Make the DHT IDs of the sybils close to the hash value of K. • Announce these sybils to the peers to poison the tables. • Does not completely eclipse a particular keyword. • Overnet uses the entire hash space for a keyword.

  22. Polluting • Publish a very large number of files using the keyword K. • This overwrites the real content previously published under K. • Their results showed that this is very effective.

  23. Pollution Results • As more polluted content is published, the true content decreases and is virtually eliminated.

  24. QUESTIONS??????

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