Network Attacks CCNA
Network Attacks CCNA

Network Attacks

Network Attacks


This topic identify security vulnerabilities.. Start learning CCNA 200-301 for free right now!!

Note: Welcome: This topic is part of Chapter 16 of the Cisco CCNA 1 course, for a better follow up of the course you can go to the CCNA 1 section to guide you through an order.

Types of Malware

The previous topic explained the types of network threats and the vulnerabilities that make threats possible. This topic goes into more detail about how threat actors gain access to network or restrict authorized users from having access.

Malware is short for malicious software. It is code or software specifically designed to damage, disrupt, steal, or inflict “bad” or illegitimate action on data, hosts, or networks. Viruses, worms, and Trojan horses are types of malware.


A computer virus is a type of malware that propagates by inserting a copy of itself into, and becoming part of, another program. It spreads from one computer to another, leaving infections as it travels. Viruses can range in severity from causing mildly annoying effects, to damaging data or software and causing denial of service (DoS) conditions. Almost all viruses are attached to an executable file, which means the virus may exist on a system but will not be active or able to spread until a user runs or opens the malicious host file or program. When the host code is executed, the viral code is executed as well. Normally, the host program keeps functioning after the virus infects it. However, some viruses overwrite other programs with copies of themselves, which destroys the host program altogether. Viruses spread when the software or document they are attached to is transferred from one computer to another using the network, a disk, file sharing, or infected email attachments.


Computer worms are similar to viruses in that they replicate functional copies of themselves and can cause the same type of damage. In contrast to viruses, which require the spreading of an infected host file, worms are standalone software and do not require a host program or human help to propagate. A worm does not need to attach to a program to infect a host and enter a computer through a vulnerability in the system. Worms take advantage of system features to travel through the network unaided.

Trojan Horses

A Trojan horse is another type of malware named after the wooden horse the Greeks used to infiltrate Troy. It is a harmful piece of software that looks legitimate. Users are typically tricked into loading and executing it on their systems. After it is activated, it can achieve any number of attacks on the host, from irritating the user (with excessive pop-up windows or changing the desktop) to damaging the host (deleting files, stealing data, or activating and spreading other malware, such as viruses). Trojan horses are also known to create back doors to give malicious users access to the system.

Unlike viruses and worms, Trojan horses do not reproduce by infecting other files. They self-replicate. Trojan horses must spread through user interaction such as opening an email attachment or downloading and running a file from the internet.

Click Play in the figure to view an animated explanation of the three types of malware.

Types of Malware Trojan Horses
Types of Malware Trojan Horses

Reconnaissance Attacks

In addition to malicious code attacks, it is also possible for networks to fall prey to various network attacks. Network attacks can be classified into three major categories:

  • Reconnaissance attacks – The discovery and mapping of systems, services, or vulnerabilities.
  • Access attacks – The unauthorized manipulation of data, system access, or user privileges.
  • Denial of service – The disabling or corruption of networks, systems, or services.

For reconnaissance attacks, external threat actors can use internet tools, such as the nslookup and whois utilities, to easily determine the IP address space assigned to a given corporation or entity. After the IP address space is determined, a threat actor can then ping the publicly available IP addresses to identify the addresses that are active. To help automate this step, a threat actor may use a ping sweep tool, such as fping or gping. This systematically pings all network addresses in a given range or subnet. This is similar to going through a section of a telephone book and calling each number to see who answers.

Click each type of reconnaissance attack tool to see an animation of the attack.

Click Play in the figure to view an animation. The threat actor is looking for initial information about a target. Various tools can be used, including Google search, the websites of organizations, whois, and more.

Internet Queries Whois
Internet Queries Whois

Click Play in the figure to view an animation. The threat initiates a ping sweep to determine which IP addresses are active.

Ping Sweeps
Ping Sweeps

Click Play in the figure to view an animation of a threat actor performing a port scan on the discovered active IP addresses.

Port Scans
Port Scans

Access Attacks

Access attacks exploit known vulnerabilities in authentication services, FTP services, and web services to gain entry to web accounts, confidential databases, and other sensitive information. An access attack allows individuals to gain unauthorized access to information that they have no right to view. Access attacks can be classified into four types: password attacks, trust exploitation, port redirection, and man-in-the middle.

Click each button for an explanation of each type of attack.

Threat actors can implement password attacks using several different methods:

  • Brute-force attacks
  • Trojan horse attacks
  • Packet sniffers

Password Attacks
Password Attacks

In a trust exploitation attack, a threat actor uses unauthorized privileges to gain access to a system, possibly compromising the target. Click Play in the figure to view an example of trust exploitation.

Trust Exploitation
Trust Exploitation

In the animation, System A trusts System B. System B trusts everyone. The threat actor wants to gain access to System A. Therefore, the threat actor compromises System B first and then can use System B to attack System A.

In a port redirection attack, a threat actor uses a compromised system as a base for attacks against other targets. The example in the figure shows a threat actor using SSH (port 22) to connect to a compromised host A. Host A is trusted by host B and, therefore, the threat actor can use Telnet (port 23) to access it.

Port Redirection
Port Redirection

In a man-in-the-middle attack, the threat actor is positioned in between two legitimate entities in order to read or modify the data that passes between the two parties. The figure displays an example of a man-in-the-middle attack.


Step 1. When a victim requests a web page, the request is directed to the threat actor's computer.

Step 2. The threat actor’s computer receives the request and retrieves the real page from the legitimate website.

Step 3. The threat actor can alter the legitimate web page and make changes to the data.

Step 4. The threat actor forwards the requested page to the victim.

Denial of Service Attacks

Denial of service (DoS) attacks are the most publicized form of attack and among the most difficult to eliminate. However, because of their ease of implementation and potentially significant damage, DoS attacks deserve special attention from security administrators.

DoS attacks take many forms. Ultimately, they prevent authorized people from using a service by consuming system resources. To help prevent DoS attacks it is important to stay up to date with the latest security updates for operating systems and applications.

Click each button for an example of DoS and distributed DoS (DDoS) attacks.

DoS attacks are a major risk because they interrupt communication and cause significant loss of time and money. These attacks are relatively simple to conduct, even by an unskilled threat actor.

Click Play in the figure to view the animation of a DoS attack.

DoS Attack
DoS Attack

A DDoS is similar to a DoS attack, but it originates from multiple, coordinated sources. For example, a threat actor builds a network of infected hosts, known as zombies. A network of zombies is called a botnet. The threat actor uses a command and control (CnC) program to instruct the botnet of zombies to carry out a DDoS attack.

Click Play in the figure to view the animation of a DDoS attack.

DDoS Attack
DDoS Attack

Lab – Research Network Security Threats

In this lab, you will complete the following objectives:

  • Part 1: Explore the SANS Website
  • Part 2: Identify Recent Network Security Threats
  • Part 3: Detail a Specific Network Security Threat

Glossary: If you have doubts about any special term, you can consult this computer network dictionary.

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