4.0 Network Security

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4.1 Explain Common Security Concepts

Last edited 300 days ago by Makiel [Muh-Keel]

CIA Triad (Confidentiality, Integrity, and Availability)

The three fundamentals of security are confidentiality, integrity, and availability (CIA), often referred to as the CIA triad. Most security issues result in a violation of at least one facet of the CIA triad.
Confidentiality To ensure confidentiality, you must prevent the disclosure of data or information to unauthorized entities. As part of confidentiality, the sensitivity level of data must be determined before putting any access controls in place. Data with a higher sensitivity level will have more access controls in place than data at a lower sensitivity level. Identification, authentication, authorization, and encryption can be used to maintain data confidentiality.
Certain information should only be available to certain people!
Access Controls can be used to restrict, well, Access.

Integrity Integrity, the second part of the CIA triad, ensures that data is protected from unauthorized modification or data corruption. The goal of integrity is to preserve the consistency of data, including data stored in files, databases, systems, and networks.
Data is stored and transferred as intended.
Any modification to the data needs to be identified.

Availability Availability means ensuring that data is accessible when and where it is needed. Only individuals who need access to data should be allowed access to that data. The two main areas where availability is affected are (1) when attacks are carried out that disable or cripple a system and (2) when service loss occurs during and after disasters. Technologies that provide fault tolerance, such as RAID or redundant sites, are examples of controls that help to improve availability.
Authorized users have day and night access to information within their permissions.
Redundancy, Fault Tolerance, and Availability go hand-in-hand.


The first line of defense in providing CIA is to know about the types of threats out there because you can't do anything to protect yourself from something you don't know about. But once you understand the threats, you can begin to design defenses to combat bad guys lurking in the depths of cyberspace just waiting for an opportunity to strike. Threats come in two forms, internal and external.
Internal Threats are those that are sourced within your own network. These attacks come from inside the firewall. Sadly, we have more to fear from our own users than we do from external hackers (maybe we should treat them better). They have already discovered and penetrated the network, which is two-thirds of the hacking process.
External Threats come from outside the firewall. These are typically hackers of all abilities. They include script kiddies (amateurs) and advanced persistent threats (APT, usually a state-sponsored team) and all types in between. Later you will learn that these two types require a different approach when performing penetration testing for vulnerabilities.


A Vulnerability is the absence of a countermeasure or a weakness in a countermeasure that is in place. Vulnerabilities can occur in software, hardware, or personnel. An example of a vulnerability is unrestricted access to a folder on a computer. Most organizations implement a vulnerability assessment to identify vulnerabilities
The Common Vulnerability Scoring System (CVSS) is a system of ranking vulnerabilities that are discovered based on predefined metrics. This system ensures that the most critical vulnerabilities can be easily identified and addressed after a vulnerability test is met.
Common Vulnerabilities and Exposures (CVE) describes a vulnerability in detail, using a number and letter system to describe what it endangers, the environment it requires to be successful, and, in many cases, the proper mitigation.
Antivirus software uses definition files that identify known malware. These files must be updated frequently, but the update process can usually be automated so that it requires no help from the user. If a new virus is created that has not yet been identified in the list, you will not be protected until the virus definition is added and the new definition file is downloaded.
This condition is known as a Zero-Day attack because it is the first day the virus has been released and therefore no known fix exists. This term may also be applied to an operating system bug that has not been corrected.


An Exploit occurs when a threat agent takes advantage of a vulnerability and uses it to advance an attack. When a network attack takes advantage of a vulnerability, it is somewhat of an indictment of the network team as most vulnerabilities can be identified and mitigated. A good example of a vulnerability that was exploited was the unpatched Apache server that was compromised and led to the Equifax breach.

Role-Based Access

Role-based access control prescribes creating roles or sets of permissions required for various job roles and assigning those permissions to security groups. When a new employee is assigned a role, they are simply placed in the group and thus inherit all required permissions.
When you create a role-based group, you should define what actions this role will be capable of. The choice of permissions or rights you assign to the group that represents this role (for example, customer service rep) should be driven by the tasks required and the resources required to do that job. This is an area where you should exercise least privilege. This principle states that no user should be given access to any resource that is not required to do their job.

Zero Trust

The Zero Trust concept supports least privilege. It prescribes that when a resource is created, the default permission should be No Access. It also means that when configuring ACLs on routers, all traffic should be blocked by default and only specific traffic allowed.

Defense in Depth

A Defense-In-Depth strategy refers to the practice of using multiple layers of security between data and the resources on which it resides and possible attackers. The first layer of a good defense-in-depth strategy is appropriate access control strategies. Access controls exist in all areas of an Information Systems (IS) infrastructure (more commonly referred to as an IT infrastructure), but a defense-in-depth strategy goes beyond access control. It also considers software development security, cryptography, and physical security.
Network Segmentation Enforcement Maintaining security in the network can be made easier by segmenting the network and controlling access from one segment to another. Segmentation can be done at several layers of the OSI model. One of the biggest reasons for implementing segmentation is for security purposes.
At layer 1, this means complete physical separation.
However, if you don't want to go with complete segmentation, you can also segment at layer 2 on switches by implementing VLANs and port security. This can prevent connections between systems that are connected to the same switch. They can also be used to organize users into common networks regardless of their physical location.
If segmentation at layer 3 is required, it's achieved using access control lists on routers to control access from one subnet to another or from one VLAN to another. Firewalls can implement these types of access lists as well.

Perimeter Network
Use a Perimeter Network—previously known as a demilitarized zone (DMZ)—for all publicly viewable servers, including web servers, FTP servers, and email relay servers. A Perimeter Network is a version of the DMZ that is created with two firewalls (each of the routers are operating as a firewall) and the DMZ (also called the perimeter between them), as shown in Figure 16.1.
An additional layer of security between the Internet and you.
In this case, two firewalling routers are used, and traffic must be inspected at both firewalls to enter the internal network. It is called a Perimeter Network (Screened Subnet) because there is a subnet between the two firewalls that can act as a DMZ for resources from the outside world.

Separation of duties is a concept that specifies that any operation that is susceptible to fraud or abuse by employees should be broken into two tasks and then these two tasks should be assigned to different individuals. While there is no guarantee that these two individuals don't collude, the chance of that occurring are much less than the chance of a single individual committing fraud.
Network Access Control (NAC) is a method of securing network hosts before they're allowed to access the network. NAC systems that control access to devices based on their security settings include Cisco's Network Admission Control (NAC) and Microsoft's Network Policy and Access Services (NPAS). These systems examine the state of a computer's operating system updates and antimalware updates before allowing access, and in some cases, they can even remediate the devices prior to permitting access.
Posture Assessment When devices attempt to access the network, the devices are examined closely, which is called a posture assessment. The following items can be checked:
Antimalware updates
Operating system updates
Windows Registry settings
When the assessment is complete and is positive, admission is granted. If problems are found, admission may be denied and the user notified that action must be taken, or the device may be directed to a remediation server that can install missing updates or quarantine the device if necessary.

Honeypots are systems strategically configured to be attractive to hackers and to lure them into spending enough time attacking them while information is gathered about the attack. Their ultimate purpose is to divert attention from valuable resources and to gather as much information about an attack as possible.
In some cases, entire networks called Honeynets are attractively configured for this purpose. You need to make sure that either of these types of systems do not provide direct connections to any important systems.
A Tarpit is a type of honeypot designed to provide a very slow connection to the hacker so that the attack takes enough time to be properly analyzed.

Authentication Methods

A whole bunch of authentication Methods are used today, and although it's important to know about the different schemes and how they work, all that knowledge doesn't make a difference if your network's users aren't schooled on how to manage their account names and passwords correctly.
Multifactor authentication is designed to add an additional level of security to the authentication process by verifying more than one characteristic of a user before allowing access to a resource. Users can be identified in one of five ways:
By something they know (password)
By something they are (retinas, fingerprint, facial recognition)
By something they possess (smart card)
By somewhere they are (location)
By something they do (behavior)
Two-Factor Authentication Method is when 2 of the above characteristics are used in conjunction to authenticate to a system.
MFA (Multifactor Authentication) is when 3+ of the above characteristics are used in unison to authenticate to a system.

Authentication, Authorization, and Accounting (AAA)

In computer security speak, AAA (triple A, like the auto club) refers to Authentication, Authorization, and Accounting. AAAA is a more robust version that adds auditing into the mix. AAA and AAAA aren't really protocols; instead, they're systematized, conceptual models for managing network security through one central location. Two common implementations of AAA are RADIUS and TACACS+.
When a TACACS+ or RADIUS session is closed, the information in the following list is logged, or accounted for. It has nothing to do with Money! This isn't a complete list; it's just meant to give you an idea of the type of accounting information TACACS+ & RADIUS gathers:
Connection start time and stop time
The number of bytes sent and received by the user
The number of packets sent and received by the user
The reason for the disconnection
RADIUS (Remote Authentication Dial-In User Service) is an authentication and accounting service that's used for verifying users over various types of links, including dial-up. Many ISPs use a RADIUS server to store the usernames and passwords of their clients in a central spot through which connections are configured to pass authentication requests.
RADIUS servers are client-server based authentication and encryption services maintaining user profiles in a central database. Client-Server means a “Client”(Host) will contact a “Server” to authenticate access to a resource.
RADIUS is also used in firewalls. When they're purposed this way, a user must provide a username and a password when they want to access a particular TCP/IP port. The firewall then contacts the RADIUS server to verify the credentials given. If the verification is successful, the user is granted access to that port.

The Terminal Access Controller Access-Control System Plus (TACACS+) protocol is also a AAA method and an alternative to RADIUS. Like RADIUS, it is capable of performing authentication on behalf of multiple wireless APs, RAS servers, or even LAN switches that are 802.1X capable. Difference is TACACS+ separates the user authentication and authorization into two distinct profiles.
Here are two major differences between TACACS+ and RADIUS:
RADIUS combines user authentication and authorization into one profile, but TACACS+ separates the two.
TACACS+ utilizes the connection-based TCP, but RADIUS uses UDP instead.

Single-Sign On

In today's modern enterprises, users can be overwhelmed by the number of points in the network where they may be challenged to identify themselves. Most users have to log onto the domain to have network access at all, and then there may be company websites that require an authentication process to access databases, SharePoint sites, secured drives, personal folders, and on and on!
When users must remember multiple passwords, as the number increases, they begin to resort to unsafe security practices such as writing passwords on sticky notes, hiding passwords in their drawers, and even sharing them with coworkers. All of these practices undermine the security of the network.
Single sign-on addresses this problem. With Single Sign-On (SSO), when the user logs into the domain, the domain controller issues them an access token. This access token contains a list of all the resources (which can include folders, drives, websites, databases, and so on) to which they should have access. As a result, anytime the user accesses a resource, the token is verified behind the scenes, and the user never needs to provide another password!


A directory service is a database designed to centralize data management regarding network subjects and objects. A typical directory contains a hierarchy that includes users, groups, systems, servers, client workstations, and so on. LDAP databases can contain extensive information about devices and users on your network.
LDAP is used with Active Directory and Apple’s Open Directory.
LDAP is used to access and updates database directories in Active Directory or Apple’s Open Directory.


Kerberos, created at MIT, isn't just a protocol, it's an entire security system that establishes a user's identity when they first log on to a system that's running it.
It employs strong encryption for all transactions and communication, and it's readily available.
The source code for Kerberos can be freely downloaded from lots of places on the Internet.
Kerberos works by issuing tickets to users who log in, kind of like going to an amusement park—as long as you have your ticket to ride, you're good to go. Even though the tickets expire quickly, they're automatically refreshed as long as you remain logged in. Because of this refresh feature, all systems participating in a Kerberos domain must have synchronized clocks.
The real negative hits happen if you have only one Kerberos authentication server—if it goes down, no one can log into the network. So when running Kerberos, having redundant servers is clearly vital. You should also know that because all users’ secret keys are stored in one centralized database, if that's compromised, you have a security tsunami on your hands.

Local Authentication

When users authenticate to their computer, the authentication can be either to a domain or to the local machine. When Local Authentication is performed, the user's local account and password are verified with the local user database.
Authentication credentials are stored on the local device.
This local user database is called Security Accounts Manager (SAM) and is located in C:\windows\system32\config\. In Linux, the database is a text file, /etc/passwd (called the password file), which lists all valid usernames and their associated information.


Another form of network access control is 802.1X. This is a standard that defines a framework for centralized port-based authentication. It can be applied to both wireless and wired networks and uses three components:
Supplicant: The user or device requesting access to the network
Authenticator: The device through which the supplicant is attempting to access the network
Authentication server: The centralized device that performs authentication
The role of the authenticator can be performed by a wide variety of network access devices, including remote access servers (both dial-up and VPN), switches, and wireless access points. The role of the authentication server can be performed by a Remote Authentication Dial-In User Service (RADIUS) or Terminal Access Controller Access-Control System Plus (TACACS+) server. The authenticator requests credentials from the supplicant and, upon receipt of those credentials, relays them to the authentication server, where they are validated. Upon successful verification, the authenticator is notified to open the port for the supplicant to allow network access.

EAP (Extensible Authentication Protocol)

Extensible Authentication Protocol (EAP) isn't a single method but an authentication framework that enhances the existing wireless 802.1X framework. The EAP framework describes a basic set of actions that will take place, and each EAP type differs in the specifics of how it operates within the framework.
EAP is used on encrypted networks to provide a secure way to send identifying information to provide network authentication. It supports various authentication methods, including token cards, smart cards, certificates, one-time passwords and public key encryption.
Extensibility is a key trait of the EAP framework. Some main features of the protocol include the following:
It provides the framework within which the various authentication methods work.
It adapts to future security needs.
It can be kept simple if that's what is wanted.
PEAP(Protected Extensible Authentication Protocol), also known as Protected EAP or simply PEAP, is a protocol that encapsulates the Extensible Authentication Protocol (EAP) within an encrypted and authenticated Transport Layer Security (TLS) tunnel.
EAP-FAST works in two stages. In the first stage, a TLS tunnel is established. Unlike PEAP, EAP-FAST's first stage is established by using a pre-shared key called a Protected Authentication Credential (PAC). In the second stage, a series of type/length/value (TLV)–encoded data is used to carry a user authentication.
EAP Transport Layer Security (EAP-TLS) is the most secure method, but it's also the most difficult to configure and maintain. To use EAP-TLS, you must install a certificate on both the authentication server and the client.

Security Risk Assessments

Security assessments are used to identify security weakness with the goal of eliminating them.
Threat Assessment Prior to performing a vulnerability or a penetration test, It’s good to know what you could be potentially going up against. This effort can be improved by following online threat feeds. Threat intelligence feeds are constantly updating streams of potential threat indicators or signals derived from a source outside of your organization. These feeds are used to inform the organization as quickly as possible about new threats that have occurred. They contain the following information:
Suspicious domains
Lists of known malware hashes
IP addresses associated with malicious activity

Vulnerability Assessment ​Part of the security policy of an organization should address the type and frequency of vulnerability scans. These scans are designed to identify any security vulnerabilities that exist. A vulnerability scanner can probe for a variety of security weaknesses, including misconfigurations, out-of-date software, missing patches, and open ports. One of the most widely used is Nessus, a proprietary vulnerability scanner developed by Tenable Network Security. A partial screen shot is shown in Figure 16.5. In the output, the issues found on a host are rated, and issues with the highest severity are at the top by default.

Penetration Testing A Penetration Test is designed to simulate an attack on a system, network, or application. Its value lies in its potential to discover security holes that may have gone unnoticed. It differs from vulnerability testing in that it attempts to exploit vulnerabilities rather than simply identify them.
Strategies for penetration testing are based on the testing objectives as defined by the organization:
Blind Test: The testing team is provided with limited knowledge of the network systems and devices, using publicly available information. The organization's security team knows that an attack is coming. This test requires more effort by the testing team.
Double-Blind Test: This test is like a blind test except the organization's security team does not know that an attack is coming. This test usually requires equal effort for both the testing team and the organization's security team.
Target Test: Both the testing team and the organization's security team are given maximum information about the network and the type of test that will occur. This is the easiest test to complete, but it will not provide a full picture of the organization's security

Business Risk Assessments

Although penetration testing can identify vulnerabilities, it is not the recommended way to do so. An organization should have a well-defined risk management process in place that includes the evaluation of risk that is present.
When this process is carried out properly, Threat Modeling (Assessing the Risks) allows organizations to identify threats and potential attacks and implement the appropriate mitigations against these threats and attacks.
Once all business assets have been identified and their value to the organization has been established, specific threats to each asset are identified. An attempt must be made to establish both the likelihood of the threat's realization and the impact to the organization if it occurs. Only then can cost-effective mitigation be identified.
Process Assessment is the examination of all processes, policies and procedures that govern the way we do things. As technologies change and more options become available, new methods and approaches may be called for. The goal is continuous improvement.
A Vendor Risk Assessment should also include a careful review of all vendor relationships, asking the following questions:
Are SLAs as robust as they should be and do they focus on security requirements?
Are we too reliant on a single vendor for critical supplies and services? Is there a single point of failure in the supply chain?
Does the access required indicate the need for additional agreements such as an interconnection agreement (Contracts between telecommunications carriers to interconnect their networks and exchange traffic)? This could be a security risk to take into account.

Security Information and Event Management (SIEM)

Security information and event management (SIEM) is a term for software products and services combining security information management (SIM) and security event management (SEM). SIEM technology provides real-time analysis of security alerts generated by network hardware and applications.
SIEM can collect useful data about the following items:
Data aggregation (combining different types of related data into one useful collection)
Forensic analysis
SIEM systems not only assess the aggregated logs in real time, they generate alerts or notifications when an issue is discovered.

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