1. EE579T/9 #1 Spring 2002 © 2000-2002, Richard A. Stanley WPI EE579T Network Security 9: An Introduction to Network-Based Attacks Prof. Richard A. Stanley

2. EE579T/9 #2 Spring 2002 © 2000-2002, Richard A. Stanley WPI Thought for the Day “Everything should be made as simple as possible. But not simpler.” Albert Einstein

3. EE579T/9 #3 Spring 2002 © 2000-2002, Richard A. Stanley WPI Overview of Tonight’s Class Review last week’s lesson Course project outlines Network attacks

4. EE579T/9 #4 Spring 2002 © 2000-2002, Richard A. Stanley WPI Projects to Present on April 17 Team 1: 802.11? –Xiangping Xu, Yang, Gao, Yingchun Xu Team 2: Mobile IP Security –Phadnis, Misra, Shetty, Subramaniam Team 3: Secure Border Gateway Protocol –Aytek, Baktir, Yadlon Team 4: Exploiting Firewall Rule Sets –Kurtz, Barrett

5. EE579T/9 #5 Spring 2002 © 2000-2002, Richard A. Stanley WPI Projects to Present on April 17 Team 5: deleted Team 6: Fibre Channel Security –Elkind, Maki, Deshpande, Nat, Rongfred Team 7: Bluetooth Security –Mason, Bouchard Team 8: Flawed WEP & Fixes –Doraisami, Shirali, Shukla, Thurston

6. EE579T/9 #6 Spring 2002 © 2000-2002, Richard A. Stanley WPI Projects to Present on April 24 Team 9: SNMP Vulnerability –Staake, Peterson, Schweinsberg, Toczek Team 10: TCP Security Flaws –Kavita, Anuj, Nikhil Team 11: Intrusion Detection –Madhavi, Shankar, Rohan, Swathi Team 12: Network Worms –Yuefeng, Wei, Xin

7. EE579T/9 #7 Spring 2002 © 2000-2002, Richard A. Stanley WPI Projects to Present on April 24 Team 13:Web Services Security –Geldmacher, Johnston, Team 14: DDoS –Hill, Voduc, Huynh Team 15: S/W Firewalls –Page, Poon, Ibrahim, Meawad, Leclerc Team 16: Honeypots –Hartling, Lawson, Posluszny, Chung

8. EE579T/9 #8 Spring 2002 © 2000-2002, Richard A. Stanley WPI Network Based Attacks Oldies and Goodies--It Isn’t Magic

9. EE579T/9 #9 Spring 2002 © 2000-2002, Richard A. Stanley WPI Word of Warning Some of the attacks about to be described are as old as network attacks themselves –This doesn’t make studying them a waste of time –There is nothing new under the sun -- old attacks keep popping up in new clothes “Those who do not study history are condemned to repeat it.” George Santayana

10. EE579T/9 #10 Spring 2002 © 2000-2002, Richard A. Stanley WPI Getting Fingered

11. EE579T/9 #11 Spring 2002 © 2000-2002, Richard A. Stanley WPI Do You Know Who?

12. EE579T/9 #12 Spring 2002 © 2000-2002, Richard A. Stanley WPI TCP Review

13. EE579T/9 #13 Spring 2002 © 2000-2002, Richard A. Stanley WPI

14. EE579T/9 #14 Spring 2002 © 2000-2002, Richard A. Stanley WPI TCP Actions Assumes IP addresses are valid and correct If sequence number received  sequence number expected, packet is refused (discarded), system waits for correctly numbered packet

15. EE579T/9 #15 Spring 2002 © 2000-2002, Richard A. Stanley WPI Sequence Number Prediction Determine server’s IP address –Sniffing packets –Trying host numbers in order –Connect w/browser, observe address in status Try addresses in the server’s address space Monitor packet sequence numbers Predict and spoof the next sequence number –Hacker now appears to be a legitimate user

16. EE579T/9 #16 Spring 2002 © 2000-2002, Richard A. Stanley WPI Purpose, Detection & Defense Once on net as an internal user, hacker can use net as a base for other attacks, or to access information on the net just spoofed Detection: look for sequential “Access denied” entries in the audit log Prevention: if available, enable real-time notification of large number of sequential access denial entries

17. EE579T/9 #17 Spring 2002 © 2000-2002, Richard A. Stanley WPI SYN Flood Send a normal SYN packet to a server, as if to open a TCP connection When the server returns a SYN/ACK packet, ignore it Send another SYN packet to the server Repeat as necessary...until server cannot handle any more

18. EE579T/9 #18 Spring 2002 © 2000-2002, Richard A. Stanley WPI FINish, But Don’t Start Attacker sends FIN packet to server, but has not previously established a TCP connection Server replies with RST packet Attacker now knows that port on that server is alive and functioning

19. EE579T/9 #19 Spring 2002 © 2000-2002, Richard A. Stanley WPI Passive Sniffing Hacker obtains access to network segment; observes and analyzes traffic –Unauthorized access to legitimate computer (packet monitors standard NT/2000 fixture) –Unauthorized added NIC on segment Purpose: gather intelligence, read traffic Defense: –Secure authentication schemes (Kerberos) –Data encryption

20. EE579T/9 #20 Spring 2002 © 2000-2002, Richard A. Stanley WPI Desynchronization Attacks Hacker forces both ends of TCP session into a desynchronized state Hacker then uses a third-party host (a computer connected to the physical segment under attack) to intercept original packets and create acceptable replacement packets that mimic the real ones that would have been exchanged NB: desynchronized  disconnected

21. EE579T/9 #21 Spring 2002 © 2000-2002, Richard A. Stanley WPI Post-Desynchronization Hijacking - 1 Assume: –hacker can listen to any packet exchanged on a TCP session –hacker can forge any kind of IP packet desired and replace the original with it –session has been desynchronized

22. EE579T/9 #22 Spring 2002 © 2000-2002, Richard A. Stanley WPI Post-Desynchronization Hijacking - 2 Client sends packet header with –SEG_SEQ = CLT_SEQ –SEG_ACK = CLT_ACK Because session has been desynchronized, client packet sequence number (CLT_SEQ) will never equal server’s expected sequence number (SVR_ACK) Server therefore discards packet

23. EE579T/9 #23 Spring 2002 © 2000-2002, Richard A. Stanley WPI Post-Desynchronization Hijacking - 3 Hacker copies server-discarded packet Hacker waits to give server time to discard the packet Sends server same packet the client did, but changes SEG_ACK, SEG_SEQ, & checksum to: –SEG_SEQ = SVR_ACK –SEG_ACK = SVR_SEQ

24. EE579T/9 #24 Spring 2002 © 2000-2002, Richard A. Stanley WPI

25. EE579T/9 #25 Spring 2002 © 2000-2002, Richard A. Stanley WPI Post-Desynchronization Hijacking - 4 The sequence numbers are now correct, so the server accepts the packet the hacker sent Hacker must produce sequence data so that –SEG_SEQ = (SEG_SEQ + CLT_TO_SVR_OFFSET) –SEG_ACK = (SEG_ACK - SVR_TO_CLT_OFFSET) Where –CLT_TO_SVR_OFFSET = SVR_ACK - CLT_SEQ –SVR_TO_CLT_OFFSET = CLT_ACK - SVR_SEQ

26. EE579T/9 #26 Spring 2002 © 2000-2002, Richard A. Stanley WPI Post-Desynchronization Hijacking - 5 Hacker now interposed between true client and server All packets now routed through hacker machine, so any desired commands can be added to / removed from the payload Server responds to both client & hacker requests; hacker filters his requests and sends client requests to true client

27. EE579T/9 #27 Spring 2002 © 2000-2002, Richard A. Stanley WPI

28. EE579T/9 #28 Spring 2002 © 2000-2002, Richard A. Stanley WPI

29. EE579T/9 #29 Spring 2002 © 2000-2002, Richard A. Stanley WPI

30. EE579T/9 #30 Spring 2002 © 2000-2002, Richard A. Stanley WPI ACK Storm Primary flaw of desynchronization attack Receipt of unacceptable packet generates ACK packet to source with expected sequence number –First ACK packet from server contains server’s own sequence number –Client refuses packet, because it did not initially send the modified-request packet –Client now sends its own ACK packet, and...

31. EE579T/9 #31 Spring 2002 © 2000-2002, Richard A. Stanley WPI The End of the Storm In theory, the ACK storm is an infinite loop BUT… –If ACK packet lost, no further ACK is sent, because the packet contains no data payload –TCP communicates over a lossy network (i.e. packets will get lost) –With non-zero packet loss, storm quickly ends –Self-regulating

32. EE579T/9 #32 Spring 2002 © 2000-2002, Richard A. Stanley WPI Early Desynchronization Attack -1 Breaks client-server connection during the setup stage –Breaks on server side –After break, hacker creates new connection with a different sequence number Hacker listens for SYN/ACK exchange Hacker then sends server a RST, then SYN/ACK with same parameters as client packet, but with different sequence number

33. EE579T/9 #33 Spring 2002 © 2000-2002, Richard A. Stanley WPI Early Desynchronization Attack -2 On receipt of hacker’s RST packet, server closes first connection, and opens new connection on same port, but with a new sequence number when it receives hacker SYN. Sends SYN/ACK to original client. Hacker intercepts server SYN/ACK and sends server its own ACK packet Server switches to synchronized connection ESTABLISHED state

34. EE579T/9 #34 Spring 2002 © 2000-2002, Richard A. Stanley WPI Early Desynchronization Attack -3 Client had already switched to ESTABLISHED state on receipt of first SYN/ACK from server Attack success depends on hacker choosing correct value of CLT_TO_SVR_OFFSET –Wrong value makes both client and hacker packets unacceptable –Produces unwanted effects, including disconnect

35. EE579T/9 #35 Spring 2002 © 2000-2002, Richard A. Stanley WPI Early Desynchronization Attack -4 The hacker now has an established connection with the server, and looks just like the real client Real client cannot establish a connection on this port until the hacker disconnects, because the server believes that the client is already connected

36. EE579T/9 #36 Spring 2002 © 2000-2002, Richard A. Stanley WPI Null Data Desynchronization TCP connection can be desynchronized by sending large amount of null data to both server and client Data not visible to client Sheer volume of data interferes with ability to maintain the TCP session, and ultimately desynchronizes connection

37. EE579T/9 #37 Spring 2002 © 2000-2002, Richard A. Stanley WPI Telnet Session Attack - 1 Hacker passively monitors session When appropriate, hacker sends large volume of null data to server Hacker sends ATK_SVR_OFFSET bytes containing sequence IAC NOP –Server interprets these as null due to NOP –Telnet daemon removes each byte pair from data stream –Reception of null data interrupts Telnet session

38. EE579T/9 #38 Spring 2002 © 2000-2002, Richard A. Stanley WPI

39. EE579T/9 #39 Spring 2002 © 2000-2002, Richard A. Stanley WPI Telnet Session Attack - 2 Server has now received commands –SVR_ACK = CLTSEQ + ATK_SVR_OFFSET –Telnet session now desynchronized Same procedure carried out with client to desynchronize Early desynchronization attack carried out Hacker now establishes Telnet session with server and client, becomes “man in middle”

40. EE579T/9 #40 Spring 2002 © 2000-2002, Richard A. Stanley WPI

41. EE579T/9 #41 Spring 2002 © 2000-2002, Richard A. Stanley WPI Some Caveats Telnet session has to be able to carry null data Timing is everything -- if null data sent at wrong time, session may simply break If your Telnet session appears unpredictable, you might be experiencing an attack

42. EE579T/9 #42 Spring 2002 © 2000-2002, Richard A. Stanley WPI More ACK Info All networks lose packets, so retransmission occurs When an active attack such as described before occurs, even more retransmission occurs than in the normal course of events Extra packets due to the ACK storms One data packet can generate 10-300 empty ACK packets

43. EE579T/9 #43 Spring 2002 © 2000-2002, Richard A. Stanley WPI Detecting Attacks Detect desynchronized states –Use packet reader (i.e., a sniffer) to view sequence numbers at both ends of a connection –Sequence numbers show if desynchronized Packet percentage counting –Collect statistics on normal network operations –Use statistics to detect packet storms resulting from attacks

44. EE579T/9 #44 Spring 2002 © 2000-2002, Richard A. Stanley WPI Spoofing “You can fool all of the people some of the time. You can fool some of the people all of the time. But you can’t fool all of the people all of the time.” Abraham Lincoln Fooling most of the people most of the time is usually good enough!

45. EE579T/9 #45 Spring 2002 © 2000-2002, Richard A. Stanley WPI IP Spoofing-1 Hacker changes masquerade host IP address to the trusted client’s address Hacker builds source route to server with direct path packets should take to/from server and back to hacker’s host, with trusted client as last hop in route to server Hacker uses source route to send client request to server What’s wrong with this picture?

46. EE579T/9 #46 Spring 2002 © 2000-2002, Richard A. Stanley WPI IP Spoofing -2 Simpler approach: wait until client system shuts down and impersonate the system –Example: Unix NFS uses IP only addresses to authenticate clients –Hacker sets up PC with name and IP address of legitimate client, then initiates connection to Unix host –Typical “insider” attack, as needs knowledge of which computers are not active

47. EE579T/9 #47 Spring 2002 © 2000-2002, Richard A. Stanley WPI Spoofing E-mail Open your email client Change the “Name” field to something else Change the “Email address” to something else Delete the Incoming Mail Server address Delete the value of Mail Server User Name If you were really bad, you would find an outgoing mail server that allowed anonymous login for outgoing mail, and put its name here The approach above is good enough to fool most people most of the time

48. EE579T/9 #48 Spring 2002 © 2000-2002, Richard A. Stanley WPI Automated Spoofing C2MYAZZ –Who knows to what this filename refers? –Hijacks session without disrupting connectivity –This clever utility exploits what was intended as a feature for convenience and backwards compatibility –So, since this is well-known, the tool must be hard to get or overtaken by events, yes?

49. EE579T/9 #49 Spring 2002 © 2000-2002, Richard A. Stanley WPI

50. EE579T/9 #50 Spring 2002 © 2000-2002, Richard A. Stanley WPI Preventing Spoofing Firewall packet filtering –Audit incoming traffic. You should never find packets with source and destination addresses in the local domain coming in from outside. BUT…this takes lots of effort –Don’t allow packets that appear to have originated locally to come in from outside Hard, especially when hacker is inside

51. EE579T/9 #51 Spring 2002 © 2000-2002, Richard A. Stanley WPI Buffer Overflows Sending oversize ICMP packets Sending IIS 3.0 a 4048 byte URL request Sending email with 256-character file name attachments to Netscape/MS email clients SMB logon to NT with incorrect data size Sending Pine user an email with “from” address > 256 characters Connect to WinGate POP3 port with user name of 256 characters

52. EE579T/9 #52 Spring 2002 © 2000-2002, Richard A. Stanley WPI What Do You Intend? Take over a session –Why? –What information do you want to get/put? Associate with a network more or less permanently Deny service to selected servers / networks / clients? Anything else?

53. EE579T/9 #53 Spring 2002 © 2000-2002, Richard A. Stanley WPI The Dreaded Cookie

54. EE579T/9 #54 Spring 2002 © 2000-2002, Richard A. Stanley WPI If You Don’t Like Cookies? Use a utility or your browser tools to remove them (IE and Netscape 6 and later) –Find them using the FIND function; they’re all over the place (especially in Windows) –But they keep coming back! In Windows, accept those you want, set the C:/Windows/Cookies folder as Read Only In Unix, make cookies.txt zero-length R/O

55. EE579T/9 #55 Spring 2002 © 2000-2002, Richard A. Stanley WPI Summary TCP/IP was not intended as a secure protocol; as a result, it has vulnerabilities that can be exploited There are many ways to get access to info There are many types of attacks that can be mounted over network connections in order to gain unauthorized access to resources Never forget, the best access is hands-on

56. EE579T/9 #56 Spring 2002 © 2000-2002, Richard A. Stanley WPI Homework - 1 1. How would you prevent post- desynchronization hijacking attacks? 2. Research attack scenarios and tools that you find in literature or on the Internet. Describe two attack scenarios and the tools required (if any) that would enable you to break into the WPI network from outside. Don’t actually break in, or try to!!

57. EE579T/9 #57 Spring 2002 © 2000-2002, Richard A. Stanley WPI Homework - 2 3. Describe how a SMURF attack works (don’t just parrot the description you find). Describe how to stop it.

58. EE579T/9 #58 Spring 2002 © 2000-2002, Richard A. Stanley WPI Assignment for Next Week Read course text, Chapter 14 Next week’s topic: More Network-Based Attacks