Denial of Service DoS and

Slide 1:Denial of Service (DoS) andDistributed Denial of Service (DDoS) Lesson 13

Slide 2:Email Flooding/bombing A form of denial of service attack. From the CERT web page: Email "bombing" is characterized by abusers repeatedly sending an identical email message to a particular address. Email "spamming" is a variant of bombing; it refers to sending email to hundreds or thousands of users (or to lists that expand to that many users). Email spamming can be made worse if recipients reply to the email, causing all the original addressees to receive the reply. It may also occur innocently, as a result of sending a message to mailing lists and not realizing that the list explodes to thousands of users, or as a result of an incorrectly set-up responder message (such as vacation(1)). Email bombing/spamming may be combined with email "spoofing" (which alters the identity of the account sending the email), making it more difficult to determine who the email is actually coming from.

Slide 3:Email Flooding

Slide 4:Email Spoofing and bombing

Slide 6:Email Bombing example

Slide 7:Email FloodingWhat can you do? From the CERT web page: A.Detection If your system suddenly appears sluggish (email is slow or doesn't appear to be sent or received), the reason may be that your mailer is trying to process a large number of messages. B.Reaction Identify the source of the email bomb/spam and configure your router (or have your Network Service Provider configure the router) to prevent incoming packets from that address. Review email headers to determine the true origin of the email. Review the information related to the email bomb/spam following relevant policies and procedures of your organization. Follow up with the site(s) you identified in your review to alert them to the activity. Contact them to alert them to the activity. NOTE: When contacting these sites, keep in mind that the abuser may be trying to hide their identity. Ensure you are up to date with the most current version of email delivery daemon (sendmail, for example) and increase logging capabilities as necessary to detect or alert you to such activity.

Slide 8:Denial of Service Attacks

Slide 9:Denial of Service Attacks

Slide 10:Denial of Service (DoS) Attacks that deny legitimate users service and access to information resources. Different ways to categorize them Nature of attack Poisoned traffic malformed or invalid data that can�t be properly handled Brute-force resource simply use up all available capacity Stateful resource take advantage of client/server relationship in protocols �target� of attack Operating system attacks target flaws in specific operating systems Networking attacks exploit inherent limitations of networking

Slide 11:Sources of the Attack Can come from many places (any place) in the network An attacker can hide the source of an attack through IP spoofing Attackers can also hide their identity by enslaving unwitting victims. �owned� or �zombie� agents When an attacker uses many zombie agents together simultaneously the result is a Distributed Denial of Service (DDoS) attack

Slide 12:IIS Attack Operating System/Poisoned Traffic attack Worked against NT 4.0 running Microsoft�s Internet Information Server version 3.0 All that was required was for the user to request a document with a very long name from the server to halt it. e.g. http://victim.com/?something=xxxxxx� A patch for this bug was issued by MS

Slide 13:Ping of Death (POD) Normal Ping utility used to determine whether another machine on the network is up. Accomplished by sending an Internet Control Message Protocol (ICMP) �echo� or �ping� packet to the target. The target replies if it is operating POD accomplished by sending packet > 64K Buffer overflow ensues causing reboot or crash Patches issued to address this attack

Slide 14:ICMP Packet Considered part of IP layer Communicates error messages and other conditions that require attention. ICMP messages are usually acted on by either the IP layer or the higher layer protocol. ICMP messages are transmitted within IP datagrams as shown:

Slide 15:ICMP packet

Slide 16:ICMP Messages

Slide 17:Smurf/ping flooding/ICMP storm Another attack that exploits the ping utility Attacker sends a large stream of spoofed ping packets to a broadcast address (an IP address that services a network of computers) All of the packets have as their source address the target�s IP address. Broadcast host will relay request to all hosts on network. Hosts reply to the victim Amount of data sent to victim is multiplied by a factor of the number of hosts in network If multiple requests sent to broadcast host, target will be overloaded with replies A Network/Brute-force attack

Slide 18:ICMP Flooding

Slide 19:SYN flooding Exploits the synchronization protocol used to initiate connections Normal process is: Initiator sends synchronization (SYN) packet Target replies with a SYN/ACK (acknowledgement) Initiator sends ACK, two machines are now ready In SYN flooding, attacker sends SYN packets with phony source address target replies with SYN/ACK but it goes nowhere target waits for ACK, eventually gives up but� if enough SYN�s received, space will fill up Network/Stateful Resource attack

Slide 20:SYN Flooding

Slide 21:SYN Attacks Syn_Flooder an example of SYN Flooding attack Land is a specialized version of SYN attack From CERT Advisory CA-97.28 - Teardrop_Land Some implementations of TCP/IP are vulnerable to packets that are crafted in a particular way (a SYN packet in which the source address and port are the same as the destination--i.e., spoofed). Land is a widely available attack tool that exploits this vulnerability. Any remote user that can send spoofed packets to a host can crash or "hang" that host. Operating System/Poisoned traffic attack A patch to fix this problem is available from vendors

Slide 22:Other DoS Attacks - Teardrop Teardrop From CERT Advisory CA-97.28 - Teardrop_Land Some implementations of the TCP/IP IP fragmentation re-assembly code do not properly handle overlapping IP fragments. Teardrop is a widely available attack tool that exploits this vulnerability. Any remote user can crash a vulnerable machine. Operating System/Poisoned traffic Patch to prevent is available from vendors Note similarity with previous exploit.

Slide 23:Other DoS Attacks - Bonk A variant of Teardrop aimed at W95 and NT From www.attrition.org/security/denial/w/bonk.dos.html Based On: teardrop.c by route|daemon9 & klepto Crashes *patched* win95/(NT?) machines. Basically, we set the frag offset > header length (teardrop reversed). There are many theories as to why this works, however i do not have the resources to perform extensive testing. Operating System/Poisoned traffic Patch to prevent is available from vendors For fun, check out http://www.attrition.org/security/denial/

Slide 24:Other DoS Attacks - WinNuke Affects Window 95/3.1/NT Caused �Blue Screen of Death� Computer recovers but Internet connection hosed, requires reboot uses Out of Band (OOB) data sent to an established connection. Windows doesn�t handle OOB well and goes into a panic. Operating System/Poisoned traffic attack

Slide 25:DDoS Attack

Slide 26:tribal flood network (TFN) DDoS TFN is made up of client and daemon programs, which implement a distributed network denial of service tool capable of waging ICMP flood, SYN flood, UDP flood, and Smurf style attacks. Remote control of a TFN is accomplished via command line execution of the client program, using any of a number of connection methods (e.g., remote shell bound to a TCP port, UDP based client/server remote shells, ICMP based client/server shells, or normal "telnet" TCP terminal sessions. Communication from the TFN client to daemons is accomplished via ICMP_ECHOREPLY (why?) packets. There is no TCP or UDP based communication between the client and daemons at all. Data inserted into echoreply packet because if sent in echo request then the daemons would all reply with echoreply thus performing a DoS on itself.Data inserted into echoreply packet because if sent in echo request then the daemons would all reply with echoreply thus performing a DoS on itself.

Slide 27:trinoo DDoS A trinoo network of at least 227 systems was used on Aug 17, 1999 to flood a single system at the University of Minnesota. The attacker(s) control one or more �master�servers, each of which can control many daemons. Remote control of the master is accomplished via a TCP connection to port 27665, after which the user must authenticate with a password. Communication between the master to daemons is via UDP packects on port 27444. When the daemon starts, it initially sends a �hello� message to the master which maintains a list of active daemons it controls. The daemons send UDP packets to random (0-64K) UDP ports on the target for a period of time (120 seconds default)

Slide 28:Stacheldraht (barbed wire) DDoS Combines features of the trinoo and the original TFN and adds encryption of communication between attacker and masters and automated updating of agents. Can do ICMP flood, SYN flood, UDP flood, and smurf style attacks. There is a limit of 1000 agents for each master Used TCP and ICMP for communication between master and agents (trinoo used UDP, TFN used ICMP)

Slide 29:Protection from DoS and DDoS Best way would seem to be to stop the attack before it happens Detect and Remove Trojans from servers, use file-integrity checking programs Block �marching orders� e.g. one method to send the �attack� order is to send an unsolicited ICMP ping response -- firewalls should be set to block this. Broadcasts should not send ping requests. Limit ability to spoof. Block the attack at the source

Slide 30:Mitigating the Effects of DoS Acknowledges that we can�t stop DoS Harden the network Avoid putting �all of your eggs in one basket� Use Load balancers can employ �delayed binds� which drop sessions can also drop �Silent� TCP sessions Adjust state limits (e.g. wait time)