A primary objective of any network intruder is to gain the privileges that are required to perform his or her dirty deeds. This normally involves logging in as a normal user and then performing some sort of privilege escalation. A vertical escalation involves obtaining root privileges, while a horizontal escalation involves gaining the privileges of some other normal user. If the other normal user has any sensitive documents in folders that he or she can access, then a horizontal escalation might be all that the intruder requires. Discretionary Access Control and Mandatory Access Control can help out, but we also want to isolate processes from each other and ensure that processes run with only the lowest possible privileges.
When planning a defense against these types of attacks, consider that the attacks could come from either outsiders or insiders...
