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Smurf Attack

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The smurf attack, named after its exploit program, is a denial-of-service  attack which uses spoofed broadcast ping messages to flood a target system.

An attacker sends forged ICMP echo packets to broadcast addresses of vulnerable networks with forged source address pointing to the target (victim) of the attack. All the systems on these networks reply to the victim with ICMP echo replies. This rapidly exhausts the bandwidth available to the target.

There is not much the victim can do, because there is no connectivity to outside as the incoming link that is overloaded with ICMP packets. However, the victim can get the subnet number used as the amplifier and contact the owner to tell them to turn off amplification (i.e. enable filtering of ICMP Echoes).

IRC servers are the primary victim to smurf attacks. Script-kiddies run programs that scan the Internet looking for "amplifiers" (i.e. subnets that will respond). They compile lists of these amplifiers and exchange them with their friends. Thus, when a victim is flooded with responses, they will appear to come from all over the Internet. On IRCs, hackers will use bots (automated programs) that connect to IRC servers and collect IP addresses. The bots then send the forged packets to the amplifiers to inundate the victim.

The attack is named "smurf" after a program that generated the attack.

Several years ago, most IP networks could lend themselves thus to smurf attacks -- in the lingo, they were "smurfable". Today, thanks largely to the ease with which administrators can make a network immune to this abuse, very few networks remain smurfable. To secure a network with a Cisco router from taking part in a smurf attack, it suffices to issue the router command:

no ip directed-broadcast .

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Smurf attack - Wikipedia, the free encyclopedia

CERT Advisory CA-1999-17 Denial-of-Service Tools

CERT Advisory CA-1998-01 Smurf IP Denial-of-Service Attacks

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Tutorial - Possible DoS (fraggle) Problem

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Smurf Attack, Fraggle Attack, Spoofing, SYN Attack definition

SMURF-Directed Broadcast Vulnerabilities

Smurfing The Latest DoS Attack

backtracking spoofed packets This survey and backtracking analysis at Oak Ridge National Laboratory is sponsored by the Office of Counter Intelligence of the US Departmant of Energy.




SMURF-Directed Broadcast Vulnerabilities

Q: Our line to the Internet seems to be full at odd times during the day, even when our server is not receiving many hits. What is going on?

A: Chances are that you are either on the receiving end of a smurf attack-in which an attacker sends out fake ICMP echo requests from your address, causing you to receive numerous echo replies--or your network is being used to amplify these broadcasts and attack someone else.

Have someone analyze the traffic filling your link to determine whether it is incoming or outgoing.

If the traffic flood is incoming, then the attack is being directed at you. If it is a smurf, then the attacking packets will originate from hundreds of different points on the Internet, so you can't do much to stop the attacks from the source. Your ISP will be able to block these packets at their router if you ask them to do so.

However, if the traffic flood is outgoing, then there is a simple solution. Turn off "directed broadcast" in all your routers and switches. This will prevent other people from directing packets to broadcast addresses within your network and using you to attack others.

Smurfing is a growing problem on the Internet, and efforts are being organized to single out and repair smurf amplifier networks. Some ISPs are starting to block all traffic to and from known amplifier networks. Other groups are amassing a list of all known amplifiers and attempting to contact network administrators for the broken networks. Surprisingly enough, a large proportion of the misconfigured networks belong to the U.S. military or to scientific and educational organizations.

If you want to test your network to see if it allows smurf amplification, there is a test page at . There are also some instructions at this site explaining how to fix the configuration of your routers.

Remember, there are two types of misconfigured networks involved in a smurf attack: the staging area and the amplifier. Both of these can be fixed by changing the router configuration.

The staging area is used to send out ping packets with a forged source address of the target victim's network. If you filter out all source addresses that are not in your assigned IP address space, then your network cannot be used as a staging area. This also reduces the risk of hacker attacks, since one reason hackers break into a server is to use it as a staging area for other attacks.

The ping packets with forged source addresses are directed at amplifier networks that do not have directed broadcasts turned off. The amplifier network will broadcast the ping packets on its internal Ethernet, and every machine on that Ethernet will respond to the ping. These amplified responses are sent to the victim, whose source address was forged on the original ping packets.

The smurf programs that originate these attacks are, in essence, harnessing the power of hundreds of computers on the Internet to amplify and focus an attack. The only way to stop this misuse of the Internet is for everyone to check their own network and fix the misconfigurations.

Site Attack Highlights Need for Web Security Precautions -IW August 10, 1998

Internet security is most often associated with simply protecting private information on Net-connected networks. But an apparent hack attack against a Utah Web hosting provider last month resulted in the deletion of hundreds of sites, and security experts said the event underscores the need for providers to vigilantly secure their Web servers.

Some customers of ProHosting Virtual Web Hosting were innocent bystanders in a battle between hacking factions for control of the business' servers, a struggle that brought down as many as 700 separate sites. Nick Wood, one of ProHosting's owners, confirmed the attack and said the security hole that led to the hack had been fixed. He said he was not sure whether the company will press charges against the suspected culprits.

ProHosting's servers were attacked by an unorganized group of hackers targeting a page belonging to Milworm, another notorious hacker gang, said John Vranesevich, founder of hacker information site AntiOnline.

Vranesevich said the hackers exploited a security hole in Eudora's Qpopper, a freeware POP3 e-mail server for Unix. The flaw allows someone with the right knowledge to take control of the server remotely. The problem exists in Qpopper version 2.41 and earlier, and Eudora has since fixed it with the release of version 2.5.

Shawn Hernan, a security expert with the Computer Emergency Response Team (CERT), a government-funded security clearinghouse located at Carnegie Mellon University, said the problem stemmed from the static size of the server program's memory buffer.

"An intruder could send a carefully crafted message to the POP server and insert code that would then be executed by that server" to gain root access on the server, the highest level of administrative access, Hernan said.

CERT issued an advisory on the Qpopper exploit shortly after the July attack on ProHosting. The problem was also discussed on the Bugtraq mailing list, which covers Unix security topics. Experts suggest--in addition to keeping up to date on the latest software security bugs through CERT or Bugtraq alerts--taking other basic precautions to guard against attacks [see box, left].

CERT's Hernan advises companies shopping around for a hosting service to ask serious questions about the host's security measures and whether they stay up to date on the latest security issues.

"If you're putting your business in the hands of another company, you need to know what their procedures and processes are, and what risks you're willing to tolerate," Hernan said. "Our experience is that those sites that practice proactive security measures are less likely to be compromised."





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