1. CSCE 815 Network Security Lecture 22 Intrusions April 10, 2003

2. – 2 – CSCE 815 Sp 03 Protocol Review IP internet protocol – routing packets through network TCP – connection oriented transport UDP – ARP – address resolution protocol *** ICMP – internet control message protocol ***over IP DHCP - Application layer – FTP, HTTP, SMTP, SNMP, SSH

3. – 3 – CSCE 815 Sp 03 Buffer Overflow comments GDB gcc –g breakpoints single step info [frame, regs, …] print [format] variable Linux vs CYGWIN

4. – 4 – CSCE 815 Sp 03 IP Spoofing Attacks Spoofing means fraudulently authenticating one machine as another Fraudulent send IP packet to A with source IP address field=“IP address of B” source IP address field=“IP address of B” Raw sockets - Blind Spoofing: TCP handshake guessing sequence numbers “Exploit code for IP Smart Spoofing ” http://www.mail-archive.com/bugtraq@securityfocushttp://www.mail-archive.com/bugtraq@securityfocus. com/msg09855.html http://www.mail-archive.com/bugtraq@securityfocus

5. – 5 – CSCE 815 Sp 03 Raw Socket Creation Reference Stevens “Unix Network Programming” Ch 25 #include int sockfd;  Create the raw socket sockfd = socket(AF_INET, SOCK_RAW, protocol)  The IP_HDRINCL socket option can be set int on = 1; setsocketopt(sockfd, IPPRTO_IP, IP_HDRINCL, &on sizeof(on))  Bind(sockfd, &addr, sizeof(addr))  Sendto(sockfd, sendbuf, len,0, dstAddr, dstAddrLen)

6. – 6 – CSCE 815 Sp 03 Preventing IP Spoofing Attacks Preventing IP spoofing have your routers reject packets with local addresses from the outside also have them reject internal packets claiming to originate from the outside authenticate packets from inside

7. – 7 – CSCE 815 Sp 03 ARP Spoofing Address resolution Protocol (ARP) IP address  hardware(ethernet) address mapping send ARP packet “who has IP address and what is your hardware address?” send ARP packet “who has IP address and what is your hardware address?” ARP cache – table of recent responses ARP Spoofing  Assume IP address “a” of trusted host  Respond to ARP packets for address “a”  Sending false hardware address (I.e. the fraud’s address) Solution: make ARP cache static (manual updates!?!)

8. – 8 – CSCE 815 Sp 03 ARP Spoofing Address resolution Protocol (ARP) IP address  hardware(ethernet) address mapping send ARP packet “who has IP address and what is your hardware address?” send ARP packet “who has IP address and what is your hardware address?” ARP cache – table of recent responses ARP Spoofing  Assume IP address “a” of trusted host  Respond to ARP packets for address “a”  Sending false hardware address (I.e. the fraud’s address) Solution: make ARP cache static (manual updates!?!)

9. – 9 – CSCE 815 Sp 03 DNS Spoofing Domain Name System (DNS) hierarchical name servers map FQDN  IP address UDP packet sent with name to name server Chinese dissidents Spoofing http://www.dit-inc.us/hj-09-02.html

10. – 10 – CSCE 815 Sp 03 Web Spoofing

11. – 11 – CSCE 815 Sp 03 Email Spoofing

12. – 12 – CSCE 815 Sp 03 Security Myth “The only secure computer is the one that is turned off and unplugged” Once connected to internet it becomes a target So shutdown all unnecessary services. Myth 2 “My firewall will stop the pesky crackers!”

13. – 13 – CSCE 815 Sp 03 The Players, Platforms and Attacks The Players: The Black Hats Script kiddies The White Hats Platforms of attackers  Windows  Linux/NetBSD/FreeBSD  OpenBSD billed as “the most secure OS freely available”Attacks Denial of Service Viruses, Trojans, malicious scripts Web defacement

14. – 14 – CSCE 815 Sp 03 Network Administrator Tools Network Administration tools (MSDOS/Windows) ipconfig ifconfig netstat /etc/… not really tools as much as files /sbin/… Find ethernet/IP addresses More tools http://newsforge.com/newsforge/02/12/12/0232235.shtml?tid= 23 http://newsforge.com/newsforge/02/12/12/0232235.shtml?tid= 23

15. – 15 – CSCE 815 Sp 03 ARP Spoofing Revisited Linux World /sbin arp Iptables, ipchains, ipfwadm Arp comand –print the table Ping somewhere then use arp to look at the table again

16. – 16 – CSCE 815 Sp 03 What is a Firewall? a choke point of control and monitoring interconnects networks with differing trust imposes restrictions on network services only authorized traffic is allowed auditing and controlling access can implement alarms for abnormal behavior is itself immune to penetration provides perimeter defence

17. – 17 – CSCE 815 Sp 03 Firewall Limitations cannot protect from attacks bypassing it eg sneaker net, utility modems, trusted organisations, trusted services (eg SSL/SSH) cannot protect against internal threats eg disgruntled employee cannot protect against transfer of all virus infected programs or files because of huge range of O/S & file types

18. – 18 – CSCE 815 Sp 03 Firewalls – Packet Filters

19. – 19 – CSCE 815 Sp 03 Firewalls – Packet Filters simplest of components foundation of any firewall system examine each IP packet (no context) and permit or deny according to rules hence restrict access to services (ports) possible default policies that not expressly permitted is prohibited that not expressly prohibited is permitted

20. – 20 – CSCE 815 Sp 03 Firewalls – Packet Filters

21. – 21 – CSCE 815 Sp 03 Attacks on Packet Filters IP address spoofing fake source address to be trusted add filters on router to block source routing attacks attacker sets a route other than default block source routed packets tiny fragment attacks split header info over several tiny packets either discard or reassemble before check

22. – 22 – CSCE 815 Sp 03 Firewalls with IPtables (Linux) IPtablesIPchainsNetfilter “10 minutes to an iptables-based Linux firewall” by Joshua Drake Joshua DrakeJoshua Drake http://www.linuxworld.com/site-stories/2001/0920.ipchains.html “Taming the Wild Netfilter” September 01, 2001 by David A. Bandel David A. BandelDavid A. Bandel http://www.linuxjournal.com/article.php?sid=4815

23. – 23 – CSCE 815 Sp 03 Firewalls with IPtables (Linux) [root@jd root]# /sbin/iptables -h iptables v1.2.1 Usage: iptables -[ADC] chain rule-specification [options] iptables -[RI] chain rulenum rule-specification [options] iptables -D chain rulenum [options] iptables -[LFZ] [chain] [options] iptables -[NX] chain iptables -E old-chain-name new-chain-name iptables -P chain target [options] iptables -h (print this help information) Commands: Either long or short options are allowed. --append -A chain Append to chain --delete -D chain Delete matching rule from chain --delete -D chain rulenum [...]

24. – 24 – CSCE 815 Sp 03 Firewalls with IPtables (Linux) No incoming traffic (tcp connections) /sbin/iptables -A INPUT -p tcp --syn -j DROP Accept incoming SSH (port 22) why? /sbin/iptables -A INPUT -p tcp --syn -s 192.168.1.110/32 -- destination-port 22 -j ACCEPT /sbin/iptables -A INPUT -p tcp --syn -j DROP Add rule to allow a web server to the chain /sbin/iptables -A INPUT -p tcp --syn -s 192.168.1.110/32 -- destination-port 22 -j ACCEPT /sbin/iptables -A INPUT -p tcp --syn --destination-port 80 -j ACCEPT /sbin/iptables -A INPUT -p tcp --syn -j DROP

25. – 25 – CSCE 815 Sp 03 Chroot Jails References: http://librenix.com/ general purpose security/Linux site http://librenix.com/ http://www.gsyc.inf.uc3m.es/~assman/jail/index.html chroot environment:

26. – 26 – CSCE 815 Sp 03 Chroot Implementation

27. – 27 – CSCE 815 Sp 03 User-mode Linux UML (binding problem) http://user-mode-linux.sourceforge.net/ creates a virtual Machine allows you to run multiple instances of Linux on the same system at the same time designed for a variety of purposes, such as kernel debugging, testing applications

28. – 28 – CSCE 815 Sp 03 Firewalls – Stateful Packet Filters examine each IP packet in context keeps tracks of client-server sessions checks each packet validly belongs to one better able to detect bogus packets out of context

29. – 29 – CSCE 815 Sp 03 Firewalls - Application Level Gateway (or Proxy)

30. – 30 – CSCE 815 Sp 03 Firewalls - Application Level Gateway (or Proxy) use an application specific gateway / proxy has full access to protocol user requests service from proxy proxy validates request as legal then actions request and returns result to user need separate proxies for each service some services naturally support proxying others are more problematic custom services generally not supported

31. – 31 – CSCE 815 Sp 03 Firewalls - Circuit Level Gateway

32. – 32 – CSCE 815 Sp 03 Firewalls - Circuit Level Gateway relays two TCP connections imposes security by limiting which such connections are allowed once created usually relays traffic without examining contents typically used when trust internal users by allowing general outbound connections SOCKS commonly used for this

33. – 33 – CSCE 815 Sp 03 Bastion Host highly secure host system potentially exposed to "hostile" elements hence is secured to withstand this may support 2 or more net connections may be trusted to enforce trusted separation between network connections runs circuit / application level gateways or provides externally accessible services

34. – 34 – CSCE 815 Sp 03 Firewall Configurations

35. – 35 – CSCE 815 Sp 03 Firewall Configurations

36. – 36 – CSCE 815 Sp 03 Firewall Configurations

37. – 37 – CSCE 815 Sp 03 Access Control given system has identified a user determine what resources they can access general model is that of access matrix with subject - active entity (user, process) object - passive entity (file or resource) access right – way object can be accessed can decompose by columns as access control lists rows as capability tickets

38. – 38 – CSCE 815 Sp 03 Access Control Matrix

39. – 39 – CSCE 815 Sp 03 Trusted Computer Systems information security is increasingly important have varying degrees of sensitivity of information cf military info classifications: confidential, secret etc subjects (people or programs) have varying rights of access to objects (information) want to consider ways of increasing confidence in systems to enforce these rights known as multilevel security subjects have maximum & current security level objects have a fixed security level classification

40. – 40 – CSCE 815 Sp 03 Bell LaPadula (BLP) Model one of the most famous security models implemented as mandatory policies on system has two key policies: no read up (simple security property) a subject can only read/write an object if the current security level of the subject dominates (>=) the classification of the object no write down (*-property) a subject can only append/write to an object if the current security level of the subject is dominated by (<=) the classification of the object

41. – 41 – CSCE 815 Sp 03 Reference Monitor

42. – 42 – CSCE 815 Sp 03 Evaluated Computer Systems governments can evaluate IT systems against a range of standards: TCSEC, IPSEC and now Common Criteria define a number of “levels” of evaluation with increasingly stringent checking have published lists of evaluated products though aimed at government/defense use can be useful in industry also

43. – 43 – CSCE 815 Sp 03 Summary have considered: firewalls types of firewalls configurations access control trusted systems