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CSCE 815 Network Security Lecture 22

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

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CSCE 815 Network Security Lecture 22

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

  2. 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. Buffer Overflow comments • GDB • gcc –g • breakpoints • single step • info [frame, regs, …] • print [format] variable • Linux vs CYGWIN

  4. 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” • Raw sockets - • Blind Spoofing: TCP handshake guessing sequence numbers • “Exploit code for IP Smart Spoofing ” • http://www.mail-archive.com/bugtraq@securityfocus. com/msg09855.html

  5. Raw Socket Creation • Reference Stevens “Unix Network Programming” Ch 25 #include <socket.h> 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. 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. 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?” • 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. 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?” • 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. 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. Web Spoofing

  11. Email Spoofing

  12. 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. 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. 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

  15. 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. 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. 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. Firewalls – Packet Filters

  19. 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. Firewalls – Packet Filters

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

  23. Firewalls with IPtables (Linux) • [root@jd root]# /sbin/iptables -hiptables v1.2.1Usage: 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. 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. Chroot Jails • References: • http://librenix.com/ general purpose security/Linux site • http://www.gsyc.inf.uc3m.es/~assman/jail/index.html • chroot environment:

  26. Chroot Implementation

  27. 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. 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. Firewalls - Application Level Gateway (or Proxy)

  30. 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. Firewalls - Circuit Level Gateway

  32. 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. 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. Firewall Configurations

  35. Firewall Configurations

  36. Firewall Configurations

  37. 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. Access Control Matrix

  39. 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. 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. Reference Monitor

  42. 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. Summary • have considered: • firewalls • types of firewalls • configurations • access control • trusted systems

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