Port Scan Attacks

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If you’re planning on taking the Security+ exam, you should have a basic understanding of port scan attacks.

For example, can you answer this question?

Q. You want to identify all of the services running on a server. Which of the following tools is the BEST choice to meet this goal?

A. Penetration test

B. Protocol analyzer

C. Sniffer

D. Port scanner

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.

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Anatomy of an Attack

From a defensive perspective, it’s valuable to understand how attackers operate. Many penetration testers use similar methodologies, so you can also apply this knowledge to penetration testing. Although there is no single definition that identifies all attackers, one thing is clear: Attackers are sophisticated and clever. They should not be underestimated.

Imagine an organization that has unlimited funds to launch attacks. They could be government employees employed by another country, or they could be a group of criminals. They may be trying to steal secrets or steal some of the millions of dollars that attackers are pocketing from businesses and individuals monthly. How will they go about it?

They often combine reconnaissance with fingerprinting techniques to identify targets. Reconnaissance provides a big-picture view of a network, including the Internet Protocol (IP) addresses of a target network. Fingerprinting then homes in on individual systems to provide details of each. Some of the attackers may be experts on reconnaissance, while others are experts on different elements of fingerprinting. Once they identify their targets, attackers use this information to launch an attack.

Identifying Open Ports with a Port Scanner

One group in the organization takes the list of IP addresses and identifies open ports on each system. As a reminder, many protocols use well-known ports. For example, Telnet uses port 23 and Hypertext Transfer Protocol (HTTP) uses port 80. If a port scanner detects port 80 is open, it’s likely that the HTTP protocol is running and it may be a web server.

Port Scan

Additionally, ports also identify applications running on a system. For example, peer-to-peer (P2P) software, used for file sharing, uses specific ports for communications with other peers on the Internet. A port scan can discover these ports and detect P2P software running on a system.

A common Transmission Control Protocol (TCP) port scan sends a TCP SYN (synchronize) packet to a specific port of a server as part of the TCP three-way handshake. If the server responds with a SYN/ACK (synchronize/acknowledge) packet, the scanner knows the port is open. However, instead of completing the three-way handshake, the scanner can send an RST (reset) packet to reset the connection and then repeat the process with a different port.

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Even though it’s not recommended for services to use ports other than the well-known ports for specific services, it is possible. Because of this, an open port doesn’t definitively say the related service or protocol is running.

Some port scanners send additional queries to the system’s open ports. For example, if port 25 is open, indicating it’s running Simple Mail Transfer Protocol (SMTP), the scanner can send SMTP queries to the system and analyze the response. These queries provide verification that the protocol is running and often include additional details on the system. Similarly, HTTP queries can identify if it’s a Windows Internet Information Services (IIS) web server or an Apache web server running on a Linux system.

Security+ Practice Test Questions

SYO-401 Practice Test Questions Now Available

Over 440 realistic Security+ practice test questions

All questions include explanations so you'll know why the correct answers are correct,

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Multiple quiz formats to let you use these questions based on the way you learn.
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 SYO-401 Practice Test Questions Now Available


INCLUDES QUESTIONS TO HELP YOU PREPARE

FOR THE NEW PERFORMANCE BASED QUESTIONS 

Bonus - Performance Based Questions

Additional Security+ questions to help you prepare for the new performance based questions. These are included with the full bank of Security+ practice test questions and are divided into different sections. For example, you'll have access to the following links:

- Performance Based Question - Set 1

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of security to mobile devices and servers in a data center. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

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You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

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You'll see a graphic explaining what you might be required to do on the actual exam related to what a forensic analyst would do during an investigation. You'll then have two questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 5

You'll see a graphic explaining what you might be required to do on the actual exam to match protocols and ports. You'll then have seven questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 6

You'll see a list of security controls along with a graphic showing devices and locations within an organization, along with instructions on what you might be required to do on the actual exam to match the controls with the devices and locations. You'll then have four questions that test your knowledge and ability to correctly answer the questions. This question also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 7

You'll see a list of authentication methods and authentication factors along with instructions on what you might be required to do on the actual exam to match the authentication methods with the authentication factors. You'll then have six questions that test your knowledge and ability to correctly answer the questions. This set also includes a link to a graphic showing the end solution for the overall performance based question simulation.

- Performance Based Question - Set 8

You'll see a graphic explaining what you might be required to do on the actual exam to match different types of attacks with the name of the attack type. You'll then have five questions that test your knowledge and ability to correctly answer the questions. This is similar to Set 2 but expands on the possibilities. The set also includes a link to a page showing the end solution for the overall performance based question simulation.

New - Performance Based Question - Set 9

New questions recently added using a different testing engine. See a demo here. This set includes drag and drop and matching questions on ports.

New - Performance Based Question - Set 10

A random set of 20 performance-based questions using drag and drop, matching, sorting, and fill in-the blank. This set includes performance-based questions on RAID.

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Get the full bank of Security+ Practice Test Questions

Each open port represents a potential attack vector, so by identifying open ports, attackers can determine the attack surface. As a reminder, you can reduce the attack surface by disabling all unused services and removing all unneeded protocols. This is a key step in hardening a system, or making it more secure from the default configuration.

Many vulnerability-scanning tools like Nmap, Netcat, and Nessus include port-scanning abilities and scan systems to determine open ports. Security professionals use these tools for vulnerability scans within their networks, but attackers also use these same tools. In addition to scanning for open ports, these tools can also fingerprint a system.

Remember this

A port scanner can help determine what services and protocols are running on a remote system by identifying open ports. Port scanners typically take additional steps to verify the port is open.


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CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

  • Introduction
  • About the exam (including types of questions and strategies for performance-based questions)
  • 100 question pre-assessment exam
  • Mastering Security Basics (full content from Chapter 1 of the study guide including the exam topic review and 20 practice test questions)
  • Exploring Control Types and Methods (full content from Chapter 2 of the study guide including the exam topic review and 20 practice test questions)
  • Understanding Basic Network Security (full content from Chapter 3 of the study guide including the exam topic review and 20 practice test questions)
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  • Security+ Acronyms

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Test your readiness with these quality materials

Random 100-question tests

Random practice tests from the all of the practice test questions in the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide. All questions include explanations so you'll know why the correct answers are correct, and why the incorrect answers are incorrect.

34 Simulated Performance-based Questions

Eight sets of performance-based questions with multiple questions in each set. These questions help you understand and prepare for performance based questions.

22 Realistic Performance-based Questions

Two new sets of performance-based questions with a total of 22 questions. These new questions use a new testing engine that includes realistic drag and drop, matching, sorting, and fill in the blank questions.

Flashcard Set

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Q. You want to identify all of the services running on a server. Which of the following tools is the BEST choice to meet this goal?

A. Penetration test

B. Protocol analyzer

C. Sniffer

D. Port scanner

Answer is D. A port scanner identifies open ports on a system and is commonly used to determine what services are running on the system.

A penetration test attempts to exploit a vulnerability.

A protocol analyzer (also called a sniffer) could analyze traffic and discover protocols in use, but this would be much more difficult than using a port scanner.

See Chapter 8 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide for more information on checking vulnerabilities.

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