There are several common types of attacks launched against systems and networks. Some of them are generic, such as denial-of-service attacks, and others are very specific. If you’re planning on taking the Security+ exam, you should have a basic understanding of smurf attack that launch an attack through amplifying networks.
For example, can you answer this question?
Q. A network administrator needs to ensure the company’s network is protected against smurf attacks. What should the network administrator do?
A. Install flood guards.
B. Use salting techniques.
C. Verify border routers block directed broadcasts.
D. Ensure protocols use timestamps and sequence numbers.
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.
How a Smurf Attack Works
A smurf attack spoofs the source address of a directed broadcast ping packet to flood a victim with ping replies. It’s worthwhile to break this down:
- A ping is normally unicast—one computer to one computer. A ping sends ICMP echo requests to one computer, and the receiving computer responds with ICMP echo responses.
- The smurf attack sends the ping out as a broadcast. In a broadcast, one computer sends the packet to all other computers in the subnet.
- The smurf attack spoofs the source IP. If the source IP address isn’t changed, the computer sending out the broadcast ping will get flooded with the ICMP replies. Instead, the smurf attack substitutes the source IP with the IP address of the victim, and the victim gets flooded with these ICMP replies.
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Smurf attacks typically use directed broadcasts with an amplifying network similar to what’s shown in the following figure. The attacker sends a directed broadcast ping through a router into another network, spoofing the source IP address with the victim’s IP address of 10.80.5.1 instead. Each of the computers in the amplifying network responds by flooding the victim with ping responses. Any network can become an amplifying network.
Smurf attack through an amplifying network
Most routers block directed broadcasts by default. This is especially important for any border routers between a public network such as the Internet and a private network. In the figure, Router 1 is a border router. Blocking directed broadcasts prevents an internal network from becoming part of an attack as an amplifying network. For example, if the attacker spoofs an IP address of a computer on the Internet, computers in the amplifying network will attack that external computer.
Remember this
Smurf attacks typically use directed broadcasts to launch attacks through amplifying networks. Disabling directed broadcasts on routers mitigates the threat. It’s especially important to ensure directed broadcasts are disabled on routers bordering on the Internet to ensure internal networks are not used as amplifying networks.
Q. A network administrator needs to ensure the company’s network is protected against smurf attacks. What should the network administrator do?
A. Install flood guards.
B. Use salting techniques.
C. Verify border routers block directed broadcasts.
D. Ensure protocols use timestamps and sequence numbers.
Answer is C. Smurf attacks are blocked by preventing routers from passing directed broadcasts, especially border routers with direct access to the Internet.
Flood guards protect against SYN (synchronize) flood attacks.
Salting techniques add additional characters to passwords to thwart brute force attacks.
Timestamps and sequence numbers are useful to protect against replay attacks, but not smurf attacks.
