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Smurf attack: What it is and how it works

A smurf attack can make computer networks inaccessible and take down entire websites. This cyber threat has the potential to cause disruption and loss of revenue and could even act as a distraction while a worse hack occurs elsewhere. In this article, we explain what smurf attacks are and how to combat them.

Smurf attack: What it is and how it works

What is a smurf attack?

A smurf attack is a kind of distributed denial of service (DDoS) attack. DDoS attacks involve flooding networks with artificially inflated traffic until they become inoperable.

In a smurf attack, a cybercriminal takes advantage of the Internet Control Message Protocol (ICMP) and overwhelms a network with bogus ICMP echo requests. An ICMP echo request is a message that is sent from one device on a network to another, initiating a response (or echo) to show the sender how far apart the network nodes are and how fast data is traveling between them.

Smurf attacks are intended to cause disruption rather than steal data or money. However, they can still aid in these other more damaging attacks by creating a distraction. While security specialists try to deal with the fallout from a smurf attack, another hack could be carried out elsewhere on the network, using the first attack as cover.

Despite how troublesome and dangerous these attacks can be, their name is deceptively unthreatening. Where does the term “smurf attack” actually come from?

Why is it called a smurf attack?

Smurf attacks are named after smurf malware, the malicious software used to execute the attack. The term “smurf” is probably a reference to the Belgian Smurfs cartoon, which focuses on a community of small blue gnome-like creatures.

The Smurfs in the cartoon are individually small and unassuming, but when working as a large group, they take on and defeat much larger opponents. This parallels the way in which ICMP echo requests, while harmless individually, can cause problems if sent in large numbers at the same time.

A sudden flood of ICMP echo requests is just one sign of a smurf attack, however.

Signs of a smurf attack

The signs of a smurf attack are largely the same as any DDoS attack. Slow network performance, an inability to communicate with other devices on your network, and complaints from users about inaccessible web pages could all indicate that an attack is in process.

In a smurf attack, the network is overloaded with traffic, which causes normal network functions to stop working. Any sign that your network is inexplicably unresponsive, despite being online, could be a red flag.

You can also invest in network monitoring software that can watch for attacks. While these tools won’t always be able to confirm that you’re dealing with a smurf attack specifically, they can alert you if a high number of DDoS indicators are present.

To really know what to look out for, however, it’s important to understand how smurf attacks actually work.

How does a smurf attack work?

Smurf attacks work because of the ICMP echo request system. Within a network, one device can “ping” another, sending a signal that then prompts a reply. This process is meant to test the distance and speed between network nodes. It is a normal function but it can be abused and used by hackers in ping flood attacks.

The process of the attack can be broken into three steps.

Malware creates a network package

The smurf malware creates a network packet, using a spoofed IP address. Pretending to have originated from the server of the soon-to-be victim, this malicious packet is then sent to the network’s router or server.

ICMP ping messages are sent to the targeted IP address

Inside the data packet is an ICMP echo request, which causes the receiving server to ping other connected devices. Many networks have IP broadcasting enabled, which means that the echo request will be sent to every other node on the network. The echoes from each ping are sent back to the spoofed source address.

Continuous “echoes” bring down the network

All the nodes on the network receive the echo request and send back a response. The sudden flood of responses slows overall network performance and could so consume network resources that legitimate users cannot access them. The attacker just needs to keep sending spoofed packets to the server, triggering wave after wave of ICMP echoes, to keep the network effectively offline.

What are the types of smurf attacks?

Smurf attacks come in two categories:

Basic smurf attack

In a basic smurf attack, one address is spoofed and all the echo requests bounce back to that source.

Advanced smurf attack

In an advanced smurf attack, multiple addresses are spoofed at once, amplifying the impact of the attack as network nodes send responses to numerous source IP addresses.

What’s the difference between a smurf attack and a DDoS attack?

A smurf attack is a kind of DDoS attack. Smurf attacks exploit particular network functions — ICMP echo request packets and IP broadcasting — but this is just a specific kind of DDoS attack.

The term DDoS covers any attack in which a network is overwhelmed by some form of traffic generated by multiple devices (using a botnet, for example) in an attempt to disrupt normal services. Another example of a DDoS attack is fraggle attack, which is sometimes confused with smurf DDoS attacks.

What is the difference between smurf and fraggle attacks?

Fraggle and smurf attacks are very similar, except for one thing. Their main point of difference is the type of traffic used to cause the denial of service.

While in smurf attacks ICMP echo requests are used to flood the network, a fraggle attack relies on spoofed UDP (User Datagram Protocol) traffic to attain that outcome. The result is exactly the same, even if the methods differ slightly.

Smurf and fraggle attacks, like all DDoS attacks, can cause users and network administrators a lot of problems, so how worried should you be about smurf attacks?

Should I be afraid of a potential smurf attack?

You have good reason to be afraid of a smurf attack. If you run a website and rely on visitors for revenue, a successful DDoS operation could cause you to lose revenue and may damage your reputation as a reliable service.

Worse still, a smurf attack could be used to distract from other threats. While you’re racing to get your network and servers back online, hackers can try to steal valuable data or infect your systems with malware.

If, while distracted by the DDoS attack, you suffer a data breach or become the victim of ransomware, your problems can be massively compounded. For all of these reasons, it is essential that you take steps to protect yourself from attacks.

How to protect yourself from smurf attacks

To limit the risks of smurf attacks, follow these steps:

  • Turn off IP broadcasting. Your network routers may have IP broadcasting enabled on them, which could allow ICMP echo requests to be sent to all nodes instead of just one. Disable this feature to limit the impact of an attack.
  • Disable the echo request function. While ICMP echos are useful for measuring the distance between nodes on a network, this is not an essential feature. You can configure devices on your network to not respond to such requests, making it almost impossible for a smurfing attack to succeed.
  • Be watchful for other attacks. When suffering DDoS attacks, be wary of other potential threats. While it’s possible that the attack is being carried out simply to cause disruption, it is likely a cover for a more insidious attack elsewhere on your network.