SecurityFocus, * I have discovered that Macintosh computers running OS9 can be used to direct a stream of 1500-byte ICMP datagrams at a target on the Internet. * These ICMP datagrams or triggered by 40-byte datagrams, so one "controller" computer with a 1.3 Mbps Internet connection can focus the output of 37 slaves (combined output 45 Mbps) and block a DS-3 link. * Please read the story below and see more verification evidence on one of the Web pages http://csc.gatech.edu/~copeland or http://people.atl.mediaone.net/jacopeland. Also see the advisories at sansat_private">http://sansat_private and certat_private">http://certat_private. * Then help get the word to owners of Macintoshes connected to cable modems, ADSL modems, or LANs to install the patch that Apple has developed (http://asu.info.apple.com/swupdates.nsf/artnum/n11559). *If you are a known responsible researcher, I can give you the C-code used to scan for OS9 Macintoshes, and the C-code to excite them into attack mode. John Copeland (please send email to 2 addresses, jacopelandat_private and jacat_private). Voice Mail: 404 894-5177 ============= The "Mac Dos Attack," a Scheme for Blocking Internet Connections By John A. Copeland Professor, Georgia Tech ECE Atlanta, GA 30332-0490 More information: http://people.atl.mediaone.net/jacopeland As part of my ongoing research on Internet data communications and cable modem operations, I have been using a second computer to monitor the data packets that travel between my cable modem and Macintosh computer at my home. Internet <---> CATV coax <---> Cable Modem <---> Mac Computer or ADSL Modem | V Monitor Computer I noticed some strange packets that were causing an unexpected response from my MacIntosh. These UDP packets were only 29 bytes (characters) long, but they caused my Macintosh to send back a 1500 byte packet. This returning packet was an Internet Control Message Protocol (ICMP) packet, a type that sometimes has priority over the TCP and UDP packets that carry data from computer to computer over the Internet. Over the period Nov. 28 to Dec. 22 I saw these packets on five occasions. The first three came from Italy, Duke University, and the Gulf via South Africa. The latter two came from the same computer in the Arab Emirates. These packets were "crafted," which means the data in them was not normal. The first three had source and destination port numbers (UDP addresses) fixed at 31790 and 31789. These numbers are normally random between 1024 and 65,565. The latter two had port numbers of 60,000 and 2140. I developed a concept of how these probe packets could be used as part of a scheme to shut down organization's connections to the Internet. To prove this scheme is feasible, I successfully wrote and tested programs to implement the scheme which is described below. The purpose of this scheme, which I call a "Mac Attack," is to generate a large amount of ICMP Internet traffic going to a specific target. This scheme can be easily replicated to attack many different targets, with little chance that the perpetrators will be caught. Phase I - Scanning A computer runs a program that sends UDP packets to every Internet address in the range of addresses that are assigned to CATV cable modems and to ADSL modems. Addresses that have Macintosh computers attached and turned on will respond with the 1500-byte ICMP packet. These addresses are kept in a list for Phase 2. I will call the Macintosh computers at these addresses "slaves." Phase 2 - Attack A computer at a location like Duke University is "root compromised." This means the aggressor group has used one of the many well-known techniques to gain the administrator password so they can load their own programs, which may be scheduled to run at a later time (like Christmas Eve or New Year's Eve). The compromised computer is given a list of addresses for 40 slaves, and the address of a specific target. The log files are erased so that no one will later be able to tell who installed the attack program. When the attack program starts running, it sends trigger packets in rotation to the forty slaves on its list. The source (return) Internet address is forged to be that of the target. The forty slaves then send a 1500 byte ICMP packet to the target each time they receive a 40-byte trigger packet. If the attack computer sends 3000 40-byte trigger packets per second (bit rate less than 1 Mbps), the slave will send 3000 1500-byte packets to the target (bit rate 45 Mbps). |-----------> Slave ---------->| Control |-----------> Slave ---------->| Computer ------->|-----------> Slave ---------->|-------> Target |-----------> Slave ---------->| | * * * | 4000 1500-byte 4000 40-B pkt/s 100 40-B pkt/s 100 1500-B pkt/s ICMP pkts/s to each slave from each slave 48 Mbps This figure shows the process of "byte amplification." The target organization, or organizations, is cut off from the Internet because it's connection, a 1.5 Mbps (million bit per second) T-1 or a 45 Mbps DS-3 digital line is swamped with ICMP packets from forty different sources. Note that 30 different T-1 connections could be swamped by varying the return addresses in the trigger packets). Recovery The FBI would have to approach the CATV company to get the owner's names and addresses at the forty computers sending ICMP packets to the target. Once a slave is located, the trigger packets are examined, but appear from the Internet source address to be coming from the target. Tracing spoofed packets (those with a forged source address) back through the Internet is practically impossible. To stop the attack, most of the slaves would have to be shut down. Their owners would not be aware that their Macintoshes were be being used to participate in the attack. After a long delay, the attack computer might be located. There would be no record of who installed the attack program, which may even have have detected it's target was operating again and erased itself. Is this scenario likely? I can think of no other purpose for the five probing UDP packets I have detected, four of which came from outside the U.S. I have written programs that scan for Macintoshes, and have used just three such Macintoshes to flood an Internet address with over 1 Mbps of ICMP packets as described above. This article omits an essential detail about the trigger packets so it is not a recipe someone could use for implementation. Apple Computer became aware on Dec. 22 of the "unintended feature" in the Macintosh Internet protocol software that is used, and is working to develop a patch for Macintosh users. Prevention People who own Macintosh computers connected to high-speed Internet connections, such as a cable modem,an ADSL modem, or a corporate LAN, should turn off those computers, or disconnect them from the network when they are not actively using the network connection. They should install the OpenTransport software patch available from Apple at http://asu.info.apple.com/swupdates.nsf/artnum/n11559. Many organizations now discard incoming ICMP Echo-Request packets at their Internet Firewall (to keep hackers from scanning their network). This will not stop the UDP scanning packets described above, and will not protect them if the incoming ICMP packets jam their connection. The Internet Service Providers (ISPs) must take action to drop long ICMP packets in the backbone networks (any packet longer than 1499 bytes, at least). Contact Information The Georgia Tech network is being shut down over the Holiday break, so my normal email address and Web page will not be available. Please send email. I will check voice mail left at my office: 404 894-5177. Please send email to: jacopelandat_private This Web site will be used while the Georgia Tech network is down: http://people.atl.mediaone.net/jacopeland For my biographical information see: http://people.atl.mediaone.net/jacopeland/jac_bio.htm
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 15:24:21 PDT