Password Cracking, Sniffing and Man-in-the Middle

1. Password Cracking, Sniffing and Man-in-the Middle • Agenda • Storing Passwords on the system • Password Cracking on Windows and Linux • Defenses against Password cracking • Address Resolution Protocol (ARP) • Sniffing • Defenses against Sniffing • Man in the Middle ECE 4112 - Internetwork Security

2. Cracking Passwords • Passwords that can be guessed easily are a problem • Lots of tools available to figure out passwords • L0phtcrack windows password cracker • “John the Ripper” Unix password cracker • Default passwords remaining on a system are a typical vulnerability ECE 4112 - Internetwork Security

3. Password storage • Password files have passwords stored in a hashed or encrypted form • Hash algorithm example is message digest 4 (MD4) • Encrypted algorithm example is Data Encryption Standard (DES) • When you use your password, it is hashed or encrypted and then compared to the stored value • Crackers use a downloaded local copy of password file on their own machine ECE 4112 - Internetwork Security

4. Storing Passwords • Systems have a file with all hashed/encrypted passwords • Windows – SAM (Security Accounts Manager) database • UNIX - /etc/passwd or /etc/shadow • Access to these files can make it easy for a hacker to break in ECE 4112 - Internetwork Security

5. Windows Passwords • Security Accounts Manager (SAM) has two versions for each password • LanMan (LM) password version for backward compatibility with windows workgroups • NT Hash – cryptographic hash for windows NT/2000 (Uses MD4) • SAM file is in \WINNT\system32\config\ directory which is a binary file that is hard to read • Back up copy stored in \WINNT\repair ECE 4112 - Internetwork Security

6. Using Passwords • System has a hashed/encrypted version of the password stored in a file • On login attempt– • system hashes/encrypts the password typed in by using for example crypt() function in linux • Compares hashed/encrypted value to stored hashed/encrypted value • Idea behind password cracking is to get a copy of the hashed/encrypted passwords and then make guesses, hash/encrypt the guess and compare ECE 4112 - Internetwork Security

7. Password Cracking • Dictionary Attack • Hackers steal a copy of the stored password file • Guess a password (may use a dictionary) • Find hash/encrypted value of the guess • Compare hash to entries from stored file • Continue this until success or out of options for password guesses. • Brute Force – Guess every possible combination of characters • Hybrid – Use dictionary but add characters to dictionary entries ECE 4112 - Internetwork Security

8. Password retrieval on Windows • Sniff the network for passwords being transmitted • From Administrator’s emergency repair disk • From back-up directory ECE 4112 - Internetwork Security

9. Password Cracking on Windows • L0phtCrack – lc4 (Windows) • Available at www.@stake.com/research/lc/ • Password Auditing and Recovery Application • Default English dictionary 50,000 words • Does “hybrid” attacks • Our free trial version does not allow brute force (for $350 can purchase with that capability) • Works on weaker LanMan (LM) as well as NT hashes • Can sniff a network for LanMan hashed passwords • Can download from a local machine or remote computer the hashed password file ECE 4112 - Internetwork Security

10. L0phtCrack (lc4) • Some statistics (from the website) • L0phtCrack obtained 18% of the passwords in 10 minutes • 90% of the passwords were recovered within 48 hours on a Pentium II/300 • The Administrator and most Domain Admin passwords were cracked ECE 4112 - Internetwork Security

11. ECE 4112 - Internetwork Security

12. Password Cracking on UNIX • John the Ripper • Available at http://www.openwall.com/john/ • Supports six hashing schemes including XP • Old Unix used /etc/passwd to store passwords • Password is stored after cryptographically altered • Various algorithms (hash/encrypted) used by various Unix platforms • /etc/password is readable by everyone • Some Unix store in a shadow password file thus /etc/passwd does not contain the passwords since they are instead in /etc/shadow or /etc/secure, only root can access these files • If shadow file used, must have root to copy ECE 4112 - Internetwork Security

13. Password retrieval on Linux • List of login names and usernames in /etc/passwd • List of encrypted passwords in /etc/shadow • Only /etc/shadow is enough to crack the passwords. • Having both files makes it easier ECE 4112 - Internetwork Security

14. John the Ripper • Combine information from /etc/passwd and /etc/shadow into one file • Use this file as input for John the Ripper • John can create guesses by • Using built-in dictionary • Using account information • Using brute-force guessing algorithm ECE 4112 - Internetwork Security

15. John the Ripper • Scrambling used for each guess • When a password is cracked, result displayed on screen • During execution of this tool, hitting any key will give current guess and status • Password complexity determines time needed for cracking them ECE 4112 - Internetwork Security

16. Defenses against Password Cracking • Select good passwords (not dictionary based) • Change regularly • Use tools to prevent easy passwords • Use password cracking tests against own systems • Protect system back ups that have password files • Unix: activate password shadowing • Windows: disable weaker LM authentication if no windows 95/98 machines on network ECE 4112 - Internetwork Security

17. Agenda • Storing Passwords on the system • Password Cracking on Windows and Linux • Defenses against Password cracking • Address Resolution Protocol (ARP) • Sniffing • Defenses against Sniffing • Man in the Middle ECE 4112 - Internetwork Security

18. What is ARP? • Address Resolution Protocol • Used to convert IP addresses to MAC addresses • Low-Level Protocol • Essential for inter-network communication • Used in networks with broadcast capabilities; usually Ethernet ECE 4112 - Internetwork Security

19. How does ARP work? • Internetwork Example • A forwards packet to Gateway • Gateway checks to see if it has the IP address in the cache • If so, change the MAC address and format packet appropriately and forward on the network • Otherwise broadcast a request on the network. B will respond with MAC address. Format packet and forward to B. ECE 4112 - Internetwork Security

20. How does ARP work? • LAN Example • A sends ARP request packet on LAN • Only the machine with matching IP responds with MAC • B caches the IP & MAC pair • Forwards all packets for same IP to the cached MAC ECE 4112 - Internetwork Security

21. Example of ARP in Use The figure shows the use of ARP when a computer is trying to contact another computer on the same LAN using ping: ECE 4112 - Internetwork Security

22. Four Types of ARP Messages ARP request ARP reply RARP request RARP reply ECE 4112 - Internetwork Security

23. Reverse Address Resolution Protocol (RARP) • Physical address of host machine is able to request its IP from a gateway server’s ARP table • A router maps the MAC address to corresponding Internet Protocol addresses • RARP client program requests from the RARP server on the router to be sent its IP address • RARP then returns the IP address to the machine which can store it for future use ECE 4112 - Internetwork Security

24. Format of ARP Message The ARP request includes: -target machine (TARGET IP) -IP address of the sender machine (SENDER IP) -physical address of the sender (SENDER HA) -physical address of target machine (TARGET HA) ECE 4112 - Internetwork Security

25. ARPPoisoning Note: ARP is stateless The malicious computer (Machine C) can send an ARP Reply to A and cause A to associate B’s IP with C’s MAC address. This will cause all messages from A to B to go to C Do the same to B ECE 4112 - Internetwork Security

26. ARPPoisoning C can now act as middle man for all communications between A and B. C can decide which packets are forwarded and which are discarded. C can also alter communications packets between A and B. ECE 4112 - Internetwork Security

27. Agenda • Storing Passwords on the system • Password Cracking on Windows and Linux • Defenses against Password cracking • Address Resolution Protocol (ARP) • Sniffing • Defenses against Sniffing • Man in the Middle ECE 4112 - Internetwork Security

28. Sniffing • Collect information being transmitted on the network • Attacker must be either on source, destination or intermediate network • Sniffed information can be stored/logged ECE 4112 - Internetwork Security

29. Sniffing traditional LANS • Traditional networks • Broadcast medium – easy to sniff attacker Data A Data A HUB Data A Data A ECE 4112 - Internetwork Security

30. Sniffing Switched LANS • Switched LANS • Difficult to do, but possible • Address Resolution Protocol Cache Poisoning - Attacker must inject packets into the network to redirect traffic • Attacker lies about the MAC address intercepts traffic • ARP tells which MAC address corresponds to which IP address ECE 4112 - Internetwork Security

31. attacker SWITCH Data A Data A Sniffing Switched LANS ECE 4112 - Internetwork Security

32. Sniffit • Easy to use sniffer • Available at: http://reptile.rug.ac.be/~coder/sniffit/sniffit.html • Can be run in interactive mode • Can be used to sniff traditional LANS • For Switched LANS, must be used with ARP Cache Poisoning tools ECE 4112 - Internetwork Security

33. Sniffit • Conditions (from the Sniffit web page): • You should be ROOT on your machine • The machine has to be connected to a network • You have to be allowed to sniff (ethical condition) ECE 4112 - Internetwork Security

34. Sniffit – Interactive mode • All TCP traffic can be viewed in main screen • Traffic from each system and port to each system and port can be seen • Has option to see data in a particular stream flow ECE 4112 - Internetwork Security

35. ethereal • From http://www.ethereal.com/ • Ethereal is a free network protocol analyzer for Unix and Windows. • It allows you to examine data from a live network or from a capture file on disk. • You can interactively browse the capture data, viewing summary and detail information for each packet. • Ethereal has several powerful features, including a rich display filter language and the ability to view the reconstructed stream of a TCP session. ECE 4112 - Internetwork Security Source: www.ethereal.com

36. Source: www.ethereal.com ECE 4112 - Internetwork Security

37. Defense against Sniffing • Transmit encrypted data across a network • Don’t use telnet, rsh,rlogin • Use Secure Shell • Use VPNs to encrypt data between systems • Use switches instead of hubs – makes sniffing more difficult ECE 4112 - Internetwork Security

38. Defense against Sniffing • For critical systems • MAC address filtering on switches • Restrict MAC addresses that can send and receive data on specific switch connectors (plugs) • Hard code ARP tables on critical systems ECE 4112 - Internetwork Security

39. Agenda • Storing Passwords on the system • Password Cracking on Windows and Linux • Defenses against Password cracking • Address Resolution Protocol (ARP) • Sniffing • Defenses against Sniffing • Man in the Middle ECE 4112 - Internetwork Security

40. Man in the Middle:Sniffing • It is the easiest attack to launch since all the packets transit through the attacker. • All the “plain text” protocols are compromised (the attacker can sniff user and password of many widely used protocol such as telnet, ftp, http) ECE 4112 - Internetwork Security

41. Man in the Middle: Hijacking • Easy to launch • It isn’t blind (the attacker knows exactly the sequence numbers of the TCP connection) ECE 4112 - Internetwork Security

42. Man in the Middle: Injecting • Possibility to add packets to an already established connection (only possible in full-duplex MITM) • The attacker can modify the sequence numbers and keep the connection synchronized while injecting packets. • If the MITM attack is a “proxy attack” it is even easier to inject (there are two distinct connections) ECE 4112 - Internetwork Security

43. Attacks examples (1)Command injection • Useful in scenarios where a one time authentication is used (e.g. RSA token). In such scenarios sniffing the password is useless, but hijacking an already authenticated session is possible • Injection of commands to the server • Emulation of fake replies to the client ECE 4112 - Internetwork Security

44. Attacks examples (2)Malicious code injection • Insertion of malicious code into web pages or mail (javascript, trojans, virus, etc) • Modification on the fly of binary files during the download phase (virus, backdoor, etc) ECE 4112 - Internetwork Security

45. Attacks examples (3)Payload modification • The attacker can modify the payload of the packets by recalculating the checksum • The length of the payload can also be changed but only in full-duplex (in this case the seq number has to be adjusted) ECE 4112 - Internetwork Security

46. Red Hat WS 4.0 Host 57.35.6.x The Lab Exercise – Set up Red Hat WS 4.0 ECE 4112 - Internetwork Security

47. The Exercise - Tools • Address Resolution Protocol • Ettercap to passively sniff a connection • Ettercap to actively disrupt a connection • Hunt to hijack a connection ECE 4112 - Internetwork Security

48. Exercise – Investigating ARP • Check ARP Table on all machines • Observe changes to the ARP table using Ethereal as unknown IP addresses are pinged • Get a better feel for ARP by making manual changes to the ARP table • Observe effects of making incorrect entries into the ARP table ECE 4112 - Internetwork Security

49. Exercise – Using Ettercap ECE 4112 - Internetwork Security

50. The Lab - Introduce Ettercap ECE 4112 - Internetwork Security