What is a smurf attack? How it works + prevention tips

Smurf attacks might conjure up images of the namesake little blue cartoon characters, and the two actually aren’t completely unrelated. Just like a village of smurfs is able to take down larger enemies by working together, a smurf attack can bring down larger networks by flooding them from individual devices across the network.

In the simplest terms, a smurf attack can overwhelm your computer to a degree that it’s inoperable. Here we’re giving an uncomplicated breakdown of what a smurf attack is, the parts that play into smurfing, plus pointers for smurf attack prevention.

The history of smurfing

In case you’re still wondering why it’s called a smurf attack, this denial-of-service attack technique is named after the DDoS.Smurf malware that’s required to execute it. It’s also a nod to fictional Smurf cartoon characters and how many small forces can cause one big change, similar to botnets.

In fact, the DDos.Smurf malware was born about a decade after the TV show. It’s believed to have first been used in the 1990s and created by hacker Dan Moschuk, aka TFreak. The first known smurf attack was in 1998 on the University of Minnesota, which resulted in computers shutting down across the state and even some data loss.

Smurf attacks had a relatively short time in the limelight, however, as manufacturers eventually disabled default ICMP Echo Replies or allowed for these settings to be configured to strengthen router security. 

How does a smurf attack work?  

In order to execute a successful smurf attack, cybercriminals will need:

• DDoS.Smurf malware to execute the attack
• A spoofed IP address, meaning a fake IP address that routes back to the smurf attack victim
• ICMP packets that overwhelm the victim’s network

To understand how a smurf attack works, you need to understand what the Internet Control Message Protocol (ICMP) is. ICMP is a protocol that diagnoses communication problems across computer networks, including whether data is indeed being communicated, or pinged, between devices.

In the case of a smurf attack, the DDoS.Smurf malware sends out ICMP Echo Requests to every device on an IP broadcast network and essentially puts a return address on it that’s a spoofed IP address of their victim. ICMP packets are typically used by network administrators to test hardware devices on the network, such as printers and routers. But when used to generate a smurf attack, they can eventually overwhelm the target device until it’s inoperable or inaccessible, resulting in a DDoS attack.

Here’s a step-by-step breakdown of how a smurf attack works:

1. DDoS.Smurf malware creates an ICMP Echo Request coming from a spoofed IP address that routes back to the smurf attack victim.
2. The ICMP Echo Request is sent to an IP broadcast network that then relays the message to every device on the network, eliciting ICMP Echo Replies.
3. The devices send ICMP Echo Replies back to the IP broadcast network, indicating the ICMP Echo Request has been received.
4. All of the replies are rerouted to the smurf attack victim, resulting in a DDoS attack. 

Smurf attack example

To help you grasp this concept, think of a smurf attack as someone pulling a prank that they’re throwing a party in your name. The prankster (the DDoS.Smurf malware) puts your return address (the spoofed IP address) on a bunch of fake invitations (ICMP Echo Requests), sends them to the post office (the IP broadcast network) that then mails them out to guests so you’re inundated with RSVPs (the ICMP Echo Replies). Talk about overwhelming. 

What is a smurf attack amplification factor?

A smurf attack’s amplification factor is determined by the number of hosts on the network. If a bogus ICMP Echo Request is sent through a broadcast network with 1,000 hosts, 1,000 replies will be relayed back per request. This means that even if an attacker lacks broadband, they can still overwhelm large networks with a single request.

Smurf attacks vs. fraggle attacks vs. ping floods

A smurf attack is similar to a fraggle attack in that they’re both DDoS techniques that aim to overwhelm your network. However, while smurf attacks rely on ICMP packets to flood a system, fraggle attacks use the User Datagram Protocol (UDP) echoes to do essentially the same thing. 

Smurf attack	DDoS attack that uses ICMP packets to flood a network
Fraggle attack	DDoS attack that uses the User Data Protocol (UDP) echoes to flood a network
Ping flood	DDoS attack that uses ICMP packets to flood a network, but without an amplification factor

Cybersecurity enthusiasts might liken a smurf attack to a ping flood in that it’s carried out by flooding a victim’s computer network with ICMP Echo Replies. However, smurf attackers have the added advantage of the amplification factor to boost their damage potential. Regardless, you don’t want to fall victim to either attack.

Types of smurf attacks

Generally, smurf attacks can be categorized as basic or advanced. The difference lies in the degree of the DDoS attack that follows.

Basic smurf attacks

A basic smurf attack results in a single network being flooded with infinite ICMP Echo Replies until the server becomes overloaded and potentially rendered inoperable.

Advanced smurf attacks

An advanced smurf attack can target multiple networks simultaneously. They begin as basic attacks, but the Echo Requests have been reconfigured to also respond to additional third-party victims, which enables the attacker to target bigger groups and larger sections of the web.

Transmission and effects

Smurf attacks may not be the most pressing cybersecurity threat these days, but it’s possible to accidentally download the Smurf Trojan from an infected website or malicious link in a spam email. The program remains dormant on your device, waiting to be activated by a remote attacker. Many Smurf Trojans are also equipped with rootkits that allow unauthorized users to gain control of a network without being detected.

At a minimum, smurf attacks will slow down victims’ networks and devices. Oftentimes smurf attacks result in DDoS attacks, which deem networks and devices inaccessible or inoperable. Worse yet, data theft can occur.

For companies, smurf attacks can cripple servers for days, resulting in losses of revenue and potentially customer satisfaction or loyalty. Thankfully, it’s relatively easy to prevent smurf attacks.

Smurfing prevention and mitigation

Mitigating smurfing attacks is all about protecting your network, and that starts with your router, namely by configuring how your routers and devices interact with ICMP packets. To this end, consider your smurf attack prevention approach twofold in that you should:

• Disable IP broadcast addressing across all of your network routers.    
• Configure your routers and devices to not forward or respond to ICMP Echo Requests.

You might also adjust your firewall to not allow pings from outside your network. Investing in a new router can help as well, as these configurations often default on newer devices.

Fictional Smurfs might be adorable, but smurf attacks are not. And even though smurfing might not be the most prevalent modern-day cyberattack, understanding what smurfing is can help you spot and stop similar DDoS attacks.

Hackers typically use malware to initiate DDoS attacks like smurf attacks. Having  antivirus software installed on your devices can alert you of potential malware attacks DDoS hackers use, and work diligently to destroy them if they're legitimate.