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  1. Outline • Definition • Point-to-point network denial of service • Smurf • Distributed denial of service attacks • Trin00, TFN, Stacheldraht, TFN2K • TCP SYN Flooding and Detection

  2. Denial of Service Attack Definition • An explicit attempt by attackers to prevent legitimate users of a service from using that service • Threat model – taxonomy from CERT • Consumption of network connectivity and/or bandwidth • Consumption of other resources, e.g. queue, CPU • Destruction or alternation of configuration information • Malformed packets confusing an application, cause it to freeze • Physical destruction or alternation of network components

  3. Status • DoS attacks increasing in frequency, severity and sophistication • 32% respondents detected DoS attacks (1999 CSI/FBI survey) • Yahoo, Amazon, eBay and MicroSoft DDoS attacked • About 4,000 attacks per week in 2000 • Internet's root DNS servers attacked on • Oct. 22, 2002, 9 out of 13 disabled for about an hour • Feb. 6, 2007, one of the servers crashed, two reportedly "suffered badly", while others saw "heavy traffic” • An apparent attempt to disable the Internet itself

  4. Two General Classes of Attacks • Flooding Attacks • Point-to-point attacks: TCP/UDP/ICMP flooding, Smurf attacks • Distributed attacks: hierarchical structures • Corruption Attacks • Application/service specific • Eg, polluting P2P systems

  5. Smurf DoS Attack 1 ICMP Echo ReqSrc: Dos Target Dest: brdct addr 3 ICMP Echo ReplyDest: Dos Target • Send ping request to brdcst addr (ICMP Echo Req) • Lots of responses: • Every host on target network generates a ping reply (ICMP Echo Reply) to victim • Ping reply stream can overload victim gateway DoSTarget DoSSource Prevention: reject external packets to brdcst address.

  6. Distributed DOS Stacheldraht is a classic example of a DDoS tool. BadGuy Unidirectional commands Handler Handler Handler Coordinating communication Agent Agent Agent Agent Agent Agent Agent Agent Agent Agent Attack traffic Victim

  7. Attack using Trin00 • In August 1999, network of > 2,200 systems took University of Minnesota offline for 3 days • scan for known vulnerabilities, then attack with UDP traffic • once host compromised, script the installation of the DDoS master agents • According to the incident report, took about 3 seconds to get root access

  8. Can you find source of attack? • Hard to find BadGuy • Originator of attack compromised the handlers • Originator not active when DDOS attack occurs • Can try to find agents • Source IP address in packets is not reliable • Need to examine traffic at many points, modify traffic, or modify routers

  9. Source Address Validity • Spoofed Source Address • random source addresses in attack packets • Subnet Spoofed Source Address- random address from address space assigned to the agent machine’s subnet • En Route Spoofed Source Address- address spoofed en route from agent machine to victim • Valid Source Address- used when attack strategy requires several request/reply exchanges between an agent and the victim machine- target specific applications or protocol features

  10. Targets of Attack • End hosts • Critical servers (disrupt C/S network) • Web, File, Authentication, Update • DNS • Infrastructure • Routers within org • All routers in upstream path

  11. The DDoS Landscape

  12. Attack Tools Over Time binary encryption Tools “stealth” / advanced scanning techniques High denial of service packet spoofing distributed attack tools sniffers Intruder Knowledge www attacks automated probes/scans GUI back doors network mgmt. diagnostics disabling audits hijacking sessions burglaries Attack Sophistication exploiting known vulnerabilities password cracking Attackers password guessing Low 2001 1980 1985 1990 1995 Source: CERT/CC

  13. (D)DoS Tools Over Time • 1996 - Point-to-point • 1997 – Combined w/ multiple tools • 1998 - Distributed (small, C/S) • 1999 - Add encryption, covert channel comms, shell features, auto-update, bundled w/rootkit • trin00, Stacheldraht, TFN, TFN2K • 2000 - Speed ups, use of IRC for C&C • 2001 - Added scanning, BNC, IRC channel hopping, worms include DDoS features • Code Red (attacked www.whitehouse.gov) • Linux “lion” worm (TFN) • 2002 - Added reflection attack • 2003 – IPv6 DDoS

  14. Outline • Definition • Point-to-point network denial of service • Smurf • Distributed denial of service attacks • Trin00, TFN, Stacheldraht, TFN2K • TCP SYN Flooding and Detection

  15. SYN Flooding Attack • 90% of DoS attacks use TCP SYN floods • Streaming spoofed TCP SYNs • Takes advantage of three way handshake • Server start “half-open” connections • These build up… until queue is full and all additional requests are blocked

  16. full duplex data: bi-directional data flow in same connection MSS: maximum segment size connection-oriented: handshaking (exchange of control msgs) init’s sender, receiver state before data exchange flow controlled: sender will not overwhelm receiver point-to-point: one sender, one receiver reliable, in-order byte steam: no “message boundaries” pipelined: TCP congestion and flow control set window size send & receive buffers TCP: Overview RFCs: 793, 1122, 1323, 2018, 2581

  17. 32 bits source port # dest port # sequence number acknowledgement number head len not used Receive window U A P R S F checksum Urg data pnter Options (variable length) application data (variable length) TCP segment structure URG: urgent data (generally not used) counting by bytes of data (not segments!) ACK: ACK # valid PSH: push data now (generally not used) # bytes rcvr willing to accept RST, SYN, FIN: connection estab (setup, teardown commands) Internet checksum (as in UDP)

  18. Recall:TCP sender, receiver establish “connection” before exchanging data segments initialize TCP variables: seq. #s buffers, flow control info (e.g. RcvWindow) client: connection initiator server: contacted by client Three way handshake: Step 1:client host sends TCP SYN segment to server specifies initial seq # no data Step 2:server host receives SYN, replies with SYNACK segment server allocates buffers specifies server initial seq. # Step 3: client receives SYNACK, replies with ACK segment, which may contain data TCP Connection Management

  19. TCP Handshake C S SYNC Listening Store data SYNS, ACKC Wait ACKS Connected

  20. SYN Flooding C S SYNC1 Listening SYNC2 Store data SYNC3 SYNC4 SYNC5

  21. Flood Detection System on Router/Gateway • Can we maintain states for each connection flow? • Stateless, simple detection system on edge (leaf) routers desired • Placement: First/last mile leaf routers • First mile – detect large DoS attacker • Last mile – detect DDoS attacks that first mile would miss • What metrics can capture the SYN flooding attacks?

  22. Step 1:client end system sends TCP FIN control segment to server Step 2:server receives FIN, replies with ACK. Closes connection, sends FIN. Step 3:client receives FIN, replies with ACK. Enters “timed wait” - will respond with ACK to received FINs Step 4:server, receives ACK. Connection closed. TCP Connection Management: Closing client server closing FIN ACK closing FIN ACK timed wait closed closed

  23. Detection Methods (I) • Utilize SYN-FIN pair behavior • Or SYNACK – FIN • Can be both on client or server side • However, RST violates SYN-FIN behavior • Passive RST: transmitted upon arrival of a packet at a closed port (usually by servers) • Active RST: initiated by the client to abort a TCP connection (e.g., Ctrl-D during a telnet session) • Often queued data are thrown away • So SYN-RSTactive pair is also normal

  24. SYN – FIN Behavior

  25. SYN – FIN Behavior • Generally every SYN has a FIN • We can’t tell if RST is active or passive • Consider 75% active

  26. Vulnerability of SYN-FIN Detection • Send out extra FIN or RST with different IP/port as SYN • Waste half of its bandwidth

  27. Detection Method II • SYN – SYN/ACK pair behavior • Hard to evade for the attacking source • Problems • Need to sniff both incoming and outgoing traffic • Only becomes obvious when really swamped

  28. False Positive Possibilities • Many new online users with long-lived TCP sessions • More SYNs coming in than FINs • An overloaded server would result in 3 SYNs to a FIN or SYN-ACK • Because clients would retransmit the SYN

  29. Tools for Network Security/Vulnerability Scanner

  30. nmap • nmap is an open-source port/security scanner • http://insecure.org/ • It’s primary function is the discovery and mapping of hosts on a network • nmap is consistently voted as one of the most used security tools

  31. nmap functions • Host Discovery – Identifying computers on a network • Port Scanning – Enumerating the open ports on one or more target computers • Version Detection – Interrogating listening network services • listening on remote computers to determine the application name and version number • OS Detection – Remotely determining the operating system from network devices

  32. Nessus • Nessus is an open-source vulnerability scanner • Public domain software, such as Nessus, isn't always inferior and sometimes it is actually superior ! • Technical support available at tenablesecurity.com • Three steps • Run a port-scan (using nmap) on the target host to determine which ports are open • Once open ports are identified, Nessus runs a set of exploits on the open ports. Nessus assumes standard processes run on standard ports (i.e., http on port 80) • Check for and reporting vulnerabilities

  33. Nessus Vulnerability Checking • Vulnerability checks are implemented through plugins. • Plugins are written in Nessus Attack Scripting Language (NASL), a scripting language optimized for custom network interaction. • New plugins are added as vulnerabilities are discovered. • Many plugins check for a vulnerability by actually exploiting the vulnerability. • The ‘safe checks’ option specifies that no vulnerability check capable of crashing a remote host be used (such as DOS attacks).

  34. Backup Slides

  35. Attack Rate Dynamics Agent machine sends a stream of packets to the victim • Constant Rate- Attack packets generated at constant rate, usually as many as resources allow • Variable Rate • Delay or avoid detection and response • Increasing Rate- gradually increasing rate causes a slow exhaustion of the victim’s resources • Fluctuating Rate- occasionally relieving the effect- victim can experience periodic service disruptions

  36. Up to 1996 • Point-to-point (single threaded) • SYN flood • Fragmented packet attacks • “Ping of Death” • “UDP kill”

  37. 1997 • Combined attacks • Targa • bonk, jolt, nestea, newtear, syndrop, teardrop, winnuke • Rape • teardrop v2, newtear, boink, bonk, frag, fucked, troll icmp, troll udp, nestea2, fusion2, peace keeper, arnudp, nos, nuclear, sping, pingodeth, smurf, smurf4, land, jolt, pepsi

  38. fapi (May 1998) UDP, TCP (SYN and ACK), ICMP Echo, "Smurf" extension Runs on Windows and Unix UDP comms One client spoofs src, the other does not Built-in shell feature Not designed for large networks (<10) Not easy to setup/control network fuck_them (ADM Crew, June 1998) Agent written in C; Handler is a shell script ICMP Echo Reply flooder Control traffic uses UDP Can randomize source to R.R.R.R(where 0<=R<=255) 1998

  39. 1999 • More robust and functional tools • trin00, Stacheldraht, TFN, TFN2K • Multiple attacks (TCP SYN flood, TCP ACK flood, UDP flood, ICMP flood, Smurf…) • Added encryption to C&C • Covert channel • Shell features common • Auto-update

  40. 2000 • More floods (ip-proto-255, TCP NULL flood…) • Pre-convert IP addresses of 16,702 smurf amplifiers • Stacheldraht v1.666 • Bundled into rootkits (tornkit includes stacheldraht)http://www.cert.org/incident_notes/IN-2000-10.html • Full control (multiple users, by nick, with talk and stats) • Omegav3 • Use of IRC for C&C • Knight • Kaiten • IPv6 DDoS • 4to6 (doesn’t require IPv6 support)

  41. Single host in DDoS

  42. 2001 • Worms include DDoS features • Code Red (attacked www.whitehouse.gov) • Linux “lion” worm (TFN) • Added scanning, BNC, IRC channel hopping (“Blended threats” term coined in 1999 by AusCERT) • “Power” bot • Modified “Kaiten” bot • Include time synchronization (?!!) • Leaves worm

  43. Power bot foo: oh damn, its gonna own shitloads foo: on start of the script it will erase everything that it has foo: then scan over foo: they only reboot every few weeks anyways foo: and it will take them 24 hours to scan the whole ip range foo: !scan status Scanner[24]:[SCAN][Status: ][IP: XX.X.XX.108][Port: 80][Found: 319] Scanner[208]:[SCAN][Status: ][IP: XXX.X.XXX.86][Port: 80][Found: 320] . . . foo: almost 1000 and we aren't even close foo: we are gonna own more than we thought foo: i bet 100thousand [11 hours later] Scanner[129]: [SCAN][Status: ][IP: XXX.X.XXX.195][Port: 80][Found: 34] Scanner[128]: [SCAN][Status: ][IP: XXX.X.XXX.228][Port: 80][Found: 67] Scanner[24]: [SCAN][Status: ][IP: XX.XX.XX.42][Port: 80][Found: 3580] Scanner[208]: [SCAN][Status: ][IP: XXX.XXX.XXX.156][Port: 80][Found: 3425] Scanner[65]: [SCAN][Status: ][IP: XX.XX.XXX.222][Port: 80][Found: 3959] bar: cool

  44. 2002 • Distributed reflected attack tools • d7-pH-orgasm • drdos (reflects NBT, TCP SYN :80, ICMP) • Reflected DNS attacks, steathly (NVP protocol) and encoded covert channel comms, closed port back door • Honeynet Project Reverse Challenge binaryhttp://project.honeynet.org/reverse/results/project/020601-Analysis-IP-Proto11-Backdoor.pdf

  45. 2003 • Slammer worm (effectively a DDoS on local infrastructure) • Windows RPC DCOM insertion vector for “blended threat” (CERT reports “thousands”) • More IPv6 DoS (requires IPv6 this time) • ipv6fuck, icmp6fuck