Chapter 12. Controlling Authorizations

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Authorizations are the privileges given to users and programs which allow them special rights. These rights limit how resources are utilized and help ensure appropriate use. Authorizations can be used either to restrict access or to grant selective access. Controlling authorization is the primary method of managing the resources which are available to users. The finer the granularity of the authorizations, the more control in assigning the right privileges for the right job. The following are some basic principles in building authorization models which support the kind of security model you have.

• That which is not specifically denied is allowed. This open environment model requires prior knowledge of everything that is to be denied so that it can be specifically denied. This creates an environment which is very difficult to adequately secure. This model is often the result of the evolution of an environment without security implementing some basic security measures. Most security signature scanning technologies, such as virus scanners , work within this model. They cannot stop an attack until they know what the attack looks like. Anything is allowed until it is determined to be dangerous.

• That which is not specifically allowed is denied. This is a closed model. Some would call it paranoid . However, it prevents unknown attacks. It also prevents users from doing anything which has not been defined as acceptable. This may slow the implementation of new systems and aggravate users. Businesses can use this model to control the consumption of resources ” requiring a business justification before allowing a behavior. Most security professionals agree that this model is required to build an environment where malicious attacks are a threat.

• Provide the minimum privileges required. This strategy of giving the minimum privileges necessary to perform the task for the minimum amount of time that they are needed is called least privileges. This minimizes the chances of misusing privileges.

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