Black Hat Europe 2000: Strategies for Defeating Distributed Attacks Simple Nomad Hacker Nomad Mobile Research Centre Occam Theorist RAZOR Security Team, Bind. View Corporation
About Myself ¨ http: //www. nmrc. org/ ¨ Currently Sr. Security Analyst for Bind. View’s RAZOR Team, http: //razor. bindview. com/
About This Presentation ¨ Assume basics – Understand IP addressing – Understand basic system administration ¨ Tools – Where to find them – Basic usage ¨ Terminology ¨ A “Network” point of view
Background ¨ Originally developed during early 1999 ¨ Concepts first discussed October 1999 ¨ Many concepts can be found in DDOS software today
Attack Recognition Basics ¨ Pattern Recognition – Examples: • Byte sequence in RAM • Packet content in a network transmission • Half opens against a server within a certain time frame – Considered “real-time”
Attack Recognition Basics Cont. ¨ Effect Recognition – Examples • Unscheduled server restart in logs • Unexplainable CPU utilization • System binaries altered – Considered “non” real-time
Attack Recognition Problems ¨ Blended “pattern” and “effect” attacks ¨ Sniffing attacks ¨ Decoys and false identification of attack source
Attack Recognition Problems Cont. ¨ Current solutions are usually “pattern” or “effect”, no real-time global solutions ¨ Existing large scale solutions can easily be defeated
Common Thwarting Techniques ¨ Rule-based systems can be tricked ¨ Log watchers can be deceived ¨ Time-based rules can be bypassed
What is Needed ¨ The “Overall Behavior Network/Host Monitoring Tool” (which doesn’t exist)
What Do We Do? ¨ “Trickle Down Security” – Solutions for distributed attacks will introduce good security overall ¨ Off-the-shelf is not enough ¨ Learn about attack types ¨ Defensive techniques
Changing Attack Patterns ¨ More large-scale attacks ¨ Better enumeration and assessment of the target by the attacker
Two Basic Distributed Attack Models ¨ Attacks that do not require direct observation of the results ¨ Attacks that require the attacker to directly observe the results
Basic Model Client Server Agent Issue commands Processes commands to agents Carries out commands
More Advanced Model Attacker Sniffed Replies Forged ICMP Timestamp Requests ICMP Timestamp Replies Target
Even More Advanced Model Attack Node Attacks or Probes Attack Node Sniffed Replies Upstream Host F i r e w a l l Target
ICMP ¨ Sweeping a network with Echo ¨ Typical alternates to ping – Timestamp – Info Request
Fun with ICMP ¨ Advanced ICMP enumeration – ICMP fingerprinting – Invalid header info to enumerate hosts
Host Enumeration #. /icmpenum -i 2 -c xxx. 218. 0 xxx. 218. 23 is up xxx. 218. 26 is up xxx. 218. 52 is up xxx. 218. 53 is up xxx. 218. 58 is up xxx. 218. 63 is up xxx. 218. 82 is up xxx. 218. 90 is up xxx. 218. 92 is up xxx. 218. 96 is up xxx. 218. 118 is up xxx. 218. 123 is up xxx. 218. 126 is up xxx. 218. 130 is up xxx. 218. 187 is up xxx. 218. 189 is up xxx. 218. 215 is up xxx. 218. 253 is up
Nmap ¨ Ping sweeps ¨ Port scanning ¨ TCP fingerprinting
Fun with Nmap ¨ Additional features – “Same segment” sniffing
Addition Probes ¨ Possible security devices – Using “bait” to fish out security mechanisms ¨ Sweep for promiscuous devices – False hosts and DNS lookups
Network Mapping VPN Checkpoint Firewall-1 Nortel Extranet xxx. 22. 7 NT cw Nortel CVX 1800 151. 164. x. xxx Linux Firewall www Sun Checkpoint Firewall-1 Solaris 2. 7 xxx. 49. 17 AIX 4. 2. 1 xxx. 48. 1 IDS? swb Cisco 7206 204. 70. xxx ftp Linux 2. 0. 38 xxx. 48. 2 Hosts Inside DMZ Internet Routers
Defensive Techniques ¨ Good security policy ¨ Split DNS – All public systems in one DNS server located in DMZ – All internal systems using private addresses with separate DNS server internally ¨ Drop/reject packets with a TTL of 1 or 0
Defensive Techniques Cont. ¨ Minimal ports open ¨ Stateful inspection firewalls ¨ Modified kernels/IDS to look for fingerprint packets
Defensive Techniques Cont. ¨ Limit ICMP inbound to host/destination unreachable ¨ Limit outbound ICMP
DMZ Server Recommendations ¨ Split services between servers ¨ Current patches ¨ Use trusted paths, anti-buffer overflow settings and kernel patches ¨ Use any built-in firewalling software ¨ Make use of built-in state tables
Firewall Rules ¨ Limit inbound to only necessary services ¨ Limit outbound via proxies to help control access ¨ Block all outbound to only necessary traffic
Intrusion Detection Systems ¨ Use only IDS’s that can be customized ¨ IDS should be capable of handling fragmented packet reassembly ¨ IDS should handle high speeds
Spoofed Packet Defenses ¨ Get TTL of suspected spoofed packet ¨ Probe the source address in the packet ¨ Compare the probe reply’s TTL to the suspected spoofed packet
Questions, etc. ¨ For followup: – http: //razor. bindview. com/ – thegnome@razor. bindview. com ¨ References: – – – – – David Dittrich’s web site http: //staff. washington. edu/dittrich/ "Network Cat and Mouse", SANS Network Security '99, New Orleans; security presentation, http: //www. sans. org "The Paranoid Network", SANS 2000, Orlando; security presentation, http: //www. sans. org NMap, http: //www. insecure. org/nmap/ Icmpenum, http: //razor. bindview. com/tools/ Martin Roesch’s web site http: //www. clark. net/~roesch/security. html “Strategies for Defeating Distributed Attacks”, http: //razor. bindview. com/publish/papers/strategies. html “Distributed Denial of Service Defense Tactics”, http: //razor. bindview. com/publish/papers/DDSA_Defense. html Ofin Arkin, “ICMP Usage in Scanning”, http: //www. syssecurity. com/archive/papers/ICMP_Scanning_v 2. 01. pdf
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