Threats, vulnerabilities, and risks

There are three key terms that you need to understand. They were defined in the previous section, but we will talk a little bit more about them since they are commonly mixed up. These terms are threat, risk, and vulnerability and they are discussed in the following sections.

Threat

A threat is anything that may exploit vulnerability in order to access, modify, or destroy information. A threat is the source and type of an attack and is what we try to defend against. Threat assessments are used to determine the best way to defend against a determined class of threat.

When we consider a communication between two authorized entities, a source (S) and a destination (D), threats can be categorized into the following four segments:

• Interception: This happens when an attacking entity has an access to a communication between two authorized entities. The entities do not realize that interception is happening and keep on with their communication normally.
• Interruption: This refers to when the attacking entity intercepts the communication. The source entity may not realize this is happening, while the destination entity has no knowledge of the communication attempt.
• Modification: This happens when the attacking entity changes the information sent between the two authorized entities. The destination entity does not realize that the information has been tampered with by the attacking entity.
• Fabrication: This happens when the attacking entity acts like the source entity. The destination entity acknowledges the communication as if it was produced by the source entity.
  

Vulnerability

Vulnerability is a weakness or a flaw in the security system of our application that may be used by a determined threat to access, modify, or destroy information. Vulnerability testing is mandatory and should be performed repeatedly to ensure the security of our application.

When a human or a system tries to exploit vulnerability, it is considered to be an attack. Some of the most common kinds of vulnerabilities that can be exploited to damage our system are as follows:

• Improper authentication: This happens when an entity claims that it has been authenticated and the software does not check whether this is true or false. This vulnerability affects our system of access control, since an attacker can evade the authentication process. A very common example of exploiting this vulnerability is modifying a cookie which has a field that determines whether the user is logged in. Setting loggedin to true can cheat the system into believing that the entity is already logged in and is therefore granted access when it should not be granted.
• Buffer overflow: This happens when the software has access to a determined amount of memory but tries to read a buffer out of the limits. For example, if the software has a buffer of size N but tries to read the position N+2, it will read information that may be used by another process. This grants access and even modifies the information that belongs to a part of the memory where the software should not have access.
• Cross-site scripting (XSS): This is a kind of vulnerability that allows a third-party to inject code in our software. It is especially common in websites, but it also applies to certain mobile applications. The most commonly used examples of XSS are the access to cookies from a different site and the injection of JavaScript into a different site.
• Input validation: When reading information provided by the user, it is always a good idea to validate the data. Not validating the data may result in an attacker introducing certain unexpected values that can cause an issue in the system.
• SQL injection: This is a kind of input validation vulnerability. It is very common to use a search feature in almost any application. The string that the user introduces in the search field is then introduced in a SQL sentence. If there is no analysis and filter of the string provided by the user, an attacker could write a SQL query that would be executed. If this is combined with a bad access control, the attacker could even delete the whole database.

Risk

A risk is the potential for an attack happening and being successful. The more sensitive the information, the higher the risk of attack, as it can cause a higher level of damage to our system. Risks are the result of a threat exploiting vulnerability and accessing, modifying, or destroying a piece of information that we want to be protected. Risk assessments are performed to identify the most critical dangers and to evaluate the potential damage. This potential damage is calculated through a state between the cost of a breach happening, which depends on how sensitive the information is, and the probability of that event, which depends on the threats and vulnerabilities that may affect the application.

As you can see, there is a very important relationship between these three terms; especially when trying to correctly identify the risk that the information stored suffers. Assessing threats and detecting vulnerabilities is crucial to the protection of the information in our application.