CS 640: Introduction to Computer NetworksThe Road AheadSecurity VulnerabilitiesWhy the Flaws?Security Flaws in IPSlide 6Ping FloodICMP AttacksRouting AttacksTCP AttacksTCP Layer AttacksSlide 12Slide 13Application Layer AttacksAn ExampleSlide 16Slide 17Slide 18Denial of ServiceSlide 20Simple DoSCoordinated DoSDistributed DoSSlide 24DDoS DefensesFirewallsFirewalls (contd…)Packet FiltersPacket Filters Contd.Slide 30Typical Firewall ConfigurationExample Firewall RulesSample Firewall RuleDefault Firewall RulesSlide 35AlternativesSlide 37Proxy FirewallSummaryCS 640: Introduction to Computer NetworksAditya AkellaLecture 25 –Network SecurityThe Road Ahead•Security Vulnerabilities•DoS and D-DoS•FirewallsSecurity Vulnerabilities•Security Problems in the TCP/IP Protocol Suite – Steve Bellovin, 1989•Attacks on Different Layers–IP Attacks–ICMP Attacks–Routing Attacks–TCP Attacks–Application Layer AttacksWhy the Flaws?•TCP/IP was designed for connectivity–Had its origins in an innocent world–Assumed to have lots of trust–Security not intrinsic to design•Host implementation vulnerabilities–Software bugs–Some elements in the specification were left to the implementersSecurity Flaws in IP•The IP addresses are filled in by the originating host–Address spoofing•Using source address for authentication–r-utilities (rlogin, rsh, rhosts etc..)InternetInternet2.1.1.1C1.1.1.1 1.1.1.2AB1.1.1.3S•Can A claim it is B to the server S?•ARP Spoofing•Can C claim it is B to the server S?• Much harder•Source Routing?Security Flaws in IP•IP fragmentation attack–End hosts need to keep the fragments till all the fragments arrive•Traffic amplification attack–IP allows broadcast destination–Problems?Ping FloodAttacking SystemInternetInternetBroadcast Enabled NetworkBroadcast Enabled NetworkVictim SystemICMP Attacks•No authentication•ICMP redirect message–Can cause the host to switch gateways•Man in the middle attack, sniffing•ICMP destination unreachable–Can cause the host to drop connection•Many more… –http://www.sans.org/rr/whitepapers/threats/477.phpRouting Attacks•Distance Vector Routing–Announce 0 distance to all other nodes•Blackhole traffic•Eavesdrop•Link State Routing–Can drop links randomly–Can claim direct link to any other router–A bit harder to attack than DV•BGP–ASes can announce arbitrary prefix–ASes can alter path–Could even happen due to misconfigurationsTCP AttacksIssues?–Server needs to keep waiting for ACK y+1–Server recognizes Client based on IP address/port and y+1ClientServerSYN xSYN y | ACK x+1ACK y+1TCP Layer Attacks•TCP SYN Flooding–Exploit state allocated at server after initial SYN packet–Send a SYN and don’t reply with ACK–Server will wait for 511 seconds for ACK–Finite queue size for incomplete connections (1024)–Once the queue is full it doesn’t accept requestsTCP Layer Attacks•TCP Session Hijack–When is a TCP packet valid?•Address/Port/Sequence Number in window–How to get sequence number?•Sniff traffic•Guess it–Many earlier systems had predictable ISN–Inject arbitrary data to the connectionTCP Layer Attacks•TCP Session Poisoning–Send RST packet•Will tear down connection–Do you have to guess the exact sequence number?•Anywhere in window is fine•For 64k window it takes 64k packets to reset•About 15 seconds for a T1Application Layer Attacks•Applications don’t authenticate properly•Authentication information in clear–FTP, Telnet, POP•DNS insecurity–DNS poisoning–DNS zone transferAn ExampleShimomura (S)Trusted (T)MitnickFinger• Finger @S• showmount –e• Send 20 SYN packets to S• Attack when no one is around• What other systems it trusts?• Determine ISN behaviorShowmount -eSYNAn ExampleShimomura (S)Trusted(T)Mitnick• Finger @S• showmount –e• Send 20 SYN packets to S• SYN flood T• Attack when no one is around• What other systems it trusts?• Determine ISN behavior• T won’t respond to packetsSyn floodXAn ExampleShimomura (S)trusted (T)Mitnick (M)• Finger @S• showmount –e• Send 20 SYN packets to S• SYN flood T• Send SYN to S spoofing as T• Send ACK to S with a guessed number• Attack when no one is around• What other systems it trusts?• Determine ISN behavior• T won’t respond to packets• S assumes that it has a session with TXSYNSYN|ACKACKAn ExampleShimomura (S)Trusted (T)Mitnick• Finger @S• showmount –e• Send 20 SYN packets to S• SYN flood T• Send SYN to S spoofing as T• Send ACK to S with a guessed number• Send “echo + + > ~/.rhosts”• Attack when no one is around• What other systems it trusts?• Determine ISN behavior• T won’t respond to packets• S assumes that it has a session with T• Give permission to anyone from anywhereX++ > rhostsDenial of Service•Objective make a service unusable, usually by overloading the server or network•Consume host resources–TCP SYN floods–ICMP ECHO (ping) floods•Consume bandwidth–UDP floods–ICMP floodsDenial of Service•Crashing the victim–Ping-of-Death–TCP options (unused, or used incorrectly)•Forcing more computation–Taking slow path in processing of packetsSimple DoSAttackerVictim Victim Victim• The Attacker usually spoofed source address to hide origin• Easy to blockCoordinated DoSAttackerVictim Victim VictimAttacker Attacker• The first attacker attacks a different victim to cover up the real attack• The Attacker usually spoofed source address to hide origin• Harder to deal withDistributed DoSAttackerHandler HandlerAgent Agent Agent Agent AgentVictimDistributed DoS•The handlers are usually very high volume servers–Easy to hide the attack packets•The agents are usually home users with DSL/Cable–Already infected and the agent installed•Very difficult to track down the attacker•How to differentiate between DDoS and Flash Crowd?–Flash Crowd Many clients using a service legitimately•Slashdot Effect•Victoria Secret Webcast–Generally the flash crowd disappears when the network is flooded–Sources in flash crowd are clustered•Also, requests have a patternDDoS Defenses•Network Capabilities–Destination explicitly decides whether or not to allow packets–Indicate decision by inserting “capabilities” in packets–Routers en route check for valid capabilities in subsequent packets–Issues?•Traffic Scrubbers–Sink all traffic to a
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