ECE-6612 csc.gatech/copeland/jac/6612/ Prof. John A. Copeland

1. ECE-6612 http://www.csc.gatech.edu/copeland/jac/6612/ Prof. John A. Copeland john.copeland@ece.gatech.edu 404 894-5177 fax 404 894-0035 Office: Klaus 3362 email or call for office visit, 404 894-5177 Chapter 10a - Firewalls 3/10/2013

2. Computer System Evolution Central Data Processing System: - with directly attached peripherals (card reader, magnetic tapes, line printer). Local Area Networks: - connects PC’s (in “terminal emulation” mode), remote terminals (next building) and mini-computers. Premises Network: - connects LANs and LAN-attached devices to each other. Enterprise-wide Network: - leased data lines (T1, DS-3) connect various offices. Internet Connectivity: - initially for email, now for Web access, e-commerce, music and video downloads, social networking, tele-commuting, Web and video conferencing, distance learning, ... . Makes the world accessible, but now the world also has access to you. 2

3. Connectivity Provided by the Georgia Backbone Network • Citizens • Schools • Contractors WWW • Libraries • City & County • Kiosks Governments Firewalls State WWW Gateway State Internet Other Agencies Agency Gateway & Web Server Agency Virtual Private Network Private Virtual Connection Agency Server LANs at Agency Offices across Georgia Non-Agency State Server 3

4. Agency Firewall - Protects Agency Subnets Agency Firewall - Protects Agency Subnets from Unwanted Connections from Unwanted Connections Subnet 1 Subnet 2 Gate- WAN Gate- way way Firewalls (and many routers) can reject: • Packets with certain source and destination addresses • Packets with certain high-level protocols (UDP, Telnet) Proxy Servers - for specific applications • Email messages assembled and inspected, then passed to internal email server machine. Prevent Cyber Loafing - Using the Internet for fun and personal business (not very effective). 4

5. Browser Web Server Application Application Router-Firewall can drop packets based on source or destination, ip address and/or port Layer Layer (HTTP) (HTTP) Port 31337 Port 80 Transport Transport Layer Layer (TCP,UDP) (TCP,UDP) Segment No. Segment No. Network Network Layer (IP) Layer (IP) IP Address 130.207.22.5 IP Address 24.88.15.22 Network Network Layer Layer Token Ring E'net Data Token Ring E'net Data Link Layer Link Layer Data-Link Layer Data Link Layer Token Ring Ethernet Token Ring E'net Phys. Phys. Layer Phys. Layer Layer Phys. Layer 5

6. Transport or App.-Layer Process Process Application Application Layer (HTTP, Layer Gateway, or Proxy (HTTP(HTTP, FTP, TELNET, FTP, TELNET, SMTP) SMTP) Transport Transport Transport Transport Layer Layer Layer Layer (TCP,UDP) (TCP, UDP) (TCP, UDP) (TCP, UDP) Network Network Network Network Layer (IP) Layer (IP) Layer (IP) Layer (IP) TR Data E'net Data Link Link E'net Data TR Data Layer Layer Link Layer Link Layer TR Phys. E'net Phys. E'net Phys. TR Phys. Layer Layer Layer Layer 6

7. Policy No outside Web access. Outside connections to Public Web Server Only. Prevent Web-Radios from eating up the available bandwidth. Prevent your network from being used for a Smuft DoS attack. Prevent your network from being tracerouted or Ping scanned. Firewall Setting Drop all outgoing packets to any IP, Port 80 Drop all incoming TCP SYN packets to any IP except 130:207:244.203, port 80 Drop all incoming UDP packets - except DNS and Router Broadcasts. Drop all ICMP packets going to a “broadcast” address (130.207.255.255 or 130.207.0.0). Drop all incoming ICMP, UDP, or TCP echo-request packets, drop all packets with TTL < 5. 7

8. Firewall Attacks IP Internal-Address Spoofing Source Routing (External Spoof) Tiny Fragment Attacks 2nd-Fragment Probes SYN-ACK Probes Internal Outbound Hacking Firewall Defense Drop all incoming packets with local source address. Drop all IP packets with Source-Routing Option. Drop all incoming packet fragments with small size. Assemble IP fragments (hard work), or at least *. Be “Stateful” -keep track of TCP outgoing SYN packets (start of all TCP connections). Drop all outgoing packets which do not have an "internal" source IP address. * Fragments after the first one have no transport header (no way to tell if it is TCP, UDP, ICMP, ... , or determine port numbers. Firewall must at least keep a temporary list of approved IP ID-Numbers based on the first fragment decision. 8

9. A Network Firewall is a single point that a Network Administrator can control, even if individual computers are managed by workers or departments. ------- Over half of corporate computer misfeasance is caused by employees who are already behind the main firewall. Solution 1 - isolate subnets with firewalls (usually routers or Ethernet switches with “filter” capabilities). Protect Finance Department from Engineering Department [Problem: internal network is much higher bit rate, firewalls more expensive]. Solution 2 - implement host-based firewalls to limit access except on certain TCP/UDP ports from specific hosts or subnets. Must be centrally managed to be economical. Solution 3 – Use a Intruder Detection System that divides the network into zones, and reports unauthorized cross-zone connections. 9

10. Stateful Firewall Local PC ip1 External Host ip2 TCP SYN establishes“state” (ip1,ip2,tcp, 33489,80) TCP SYN-ACK or RESET or relatedICMP established “state” (ip1,ip2,tcp, 33489,80) TCP ACK’s established “state” (ip1,ip2,tcp, 33489,80) TCP or UDP or ICMP Not part of an established “state” 10

11. # iptables -L -n Chain INPUT (policy DROP) target prot opt source destination ACCEPT tcp -- 143.218.132.0/25 0.0.0.0/0 ACCEPT tcp -- 130.207.225.0/24 0.0.0.0/0 ACCEPT all -- 79.76.0.0/16 0.0.0.0/0 tcp dpt:22 ACCEPT tcp -- 130.207.152.119 0.0.0.0/0 tcp dpt:22 ACCEPT tcp -- 143.215.151.0/24 0.0.0.0/0 ACCEPT udp -- 64.192.0.0/10 0.0.0.0/0 tcp dpt:22 ACCEPT tcp -- 69.59.0.0/16 0.0.0.0/0 tcp dpt:22 ACCEPT tcp -- 24.0.0.0/8 0.0.0.0/0 tcp dpt:22 DROP all -- 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy DROP) target prot opt source destination DROP all -- anywhere anywhere Chain OUTPUT (policy DROP) target prot opt source destination ACCEPT icmp -- anywhere 10.0.0.0/24 ACCEPT icmp -- anywhere anywhere state RELATED,ESTABLISHED A “-n” option speeds up iptables because it stops reverse lookups. Also beneficial for “route”, “netstat”, … . 11

12. Uncomplicated Firewall (UFW) for Ubuntu (LINUX) $ ufw status numbered Status: active To Action From -- ------ ---- [ 1] 8822/tcp ALLOW IN 130.207.150.144 [ 2] Anywhere ALLOW IN 143.215.138.0/25 [ 3] 8822/tcp ALLOW IN 130.207.225.103 [ 4] 8822/tcp ALLOW IN 78.88.0.0/16 [ 5] 8822/tcp ALLOW IN 80.55.0.0/16 [ 6] Anywhere DENY IN Anywhere $ ufw insert 1 allow proto tcp from 130.207.0.0/16 to any port 8822 Rule Inserted $ ufw activate (changes iptables configuration) 12

13. NAT - Network Address Translation Web Server 130.27.8.35 Internet To 24.88.48.47:y from 130.27.8.35:80 To 130.27.8.35:80 from 24.88.48.47:y 3 2 x & y are high number ephemeral client ports. Simple NATs, use x=y Router 24.88.48.47 with NAT 4 To 192.168.0.20:x from 130.27.8.35:80 To 130.27.8.35:80 from 192.168.0.20:x 1 Host 192.168.0.10 Web Client 192.168.0.20 Host 192.168.0.30 Host 192.168.0.40 Web Server port 80 FTP Server port 21 Local Web client accessing an external Web server 13

14. FTP Client 130.27.8.35 Internet To 130.27.8.35: x from 24.88.48.47:21 To 24.88.48.47: 21 from 130.27.8.35:x Forwarding Table Port 80 -> .10 Port 21 -> .30 1 4 Router 24.88.48.47 with NAT 2 3 To 130.27.8.35:y from 192.168.0.20:21 To 192.168.0.30:21 from 130.27.8.35:y Host 192.168.0.10 Host 192.168.0.20 Host 192.168.0.30 Host 192.168.0.40 Web Server port 80 FTP Server port 21 External FTP client accessing a local FTP server 14

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16. Home Routers allow incoming connections based on server port New Home Routers also allow port translation (e.g., 2222 -> 22) 16

17. Combined Firewalls and IDS (see also: IBM Proventia - www.iss.net) 17

18. Protocol Anomaly Detection WatchGuard Transparent Application layer proxies examine entire connection data streams, identifying protocol anomalies and discarding harmful or questionable information. In addition, WatchGuard firewalls perform: * Packet Handling - prevents packets from entering the network until they are reassembled and examined. * Packet Reassembly - reassembles packet fragments to prevent fragment overlap attacks such as Teardrop and other Layer 3 protocol anomaly based attacks. Signature Element Analysis Rather than using signatures that precisely identify specific attacks, WatchGuard systems look at what any attack of a certain type (e.g., e-mail) must do to succeed (e.g., auto-execute an attachment). With rule sets, you can choose to allow or deny traffic, or even deny all traffic from a source for a specific period. In addition to rigorous rule sets, the firewall processes policy-based configurations, and management subsystems perform state and content analysis. These processes protect against entire known and unknown attack classes, and can narrow the vulnerability window without having to make you wait for updated attack-specific signatures. Behavior-Based Analysis Although behavior-based intrusion detection is a relatively new technology, WatchGuard has mechanisms in place within the firewall to identify known attack behaviors, such as: * Port scans and probes * Spoofing * SYN flood attacks * DoS and DDoS attacks * The misuse of IP options such as source routing from www.watchguard.com 18

19. Network Operations * Resolve network performance issues in minutes * Provides enterprise network visibility down to user level * Troubleshoots network incidents at 1/3 the time of point solutions * Analyzes NetFlow / sFlow to facilitate capacity planning and traffic engineering Network Security * Detects attacks that bypass signature based, perimeter defenses * Leverages flow data, including packet capture, to reduce security risks by 90% * Enforces policies and assures compliance with agent-free user identity tracking * Delivers scalable, robust security and risk management from www.lancope.com 19 (also see http://users.ece.gatech.edu/~copeland/jac/lancope/index.html)