Chapter 15: System Security (3721)

Chapter 15: System Security (3721)

1. Security, on the other hand, requires not only an adequate protection system but also consideration of the external environment

2. Computer resources must be guarded against unauthorized access, malicious destruction or alteration, and accidental introduction of inconsistency

3. 15.1 The Security Problem

   • We say that a system is secure if its resources are used and accessed as intended under all circumstances.
   • a threat is the potential for a security violation
   • an attack is the attempt to break security.
   • • Breach of confidentiality. This type of violation involves unauthorized reading of data (or theft of information).
   • • Breach of integrity. This violation involves unauthorized modification of data.
   • • Breach of availability. This violation involves unauthorized destruction of data
   • • Theft of service. This violation involves unauthorized use of resources.
   • • Denial of service. This violation involves preventing legitimate use of the system. Denial-of-service (DOS) attacks are sometimes accidental.
   • The most common is masquerading, in which one participant in a communication pretends to be someone else (another host or another person).
   • A replay attack consists of the malicious or fraudulent repeat of a valid data transmission.
   • man-in-the-middle attack, in which an attacker sits in the data flow of a communication, masquerading as the sender to the receiver, and vice versa
   • To protect a system, we must take security measures at four levels:
     • 1. Physical. The site or sites containing the computer systems must be physically secured against armed or surreptitious entry by intruders.
     • 2. Human. Authorization must be done carefully to assure that only appropriate users have access to the system
       • social engineering. One type of social-engineering attack is phishing.
       • dumpster diving, a general term for attempting to gather information in order to gain unauthorized access
     • 3. Operating system. The system must protect itself from accidental or purposeful security breaches
     • 4. Network. Intercepting these data could be just as harmful as breaking into a compute

4. 15.2 Program Threats

   • Processes, along with the kernel, are the only means of accomplishing work on a computer.
   • 15.2.1 Trojan Horse
     • A code segment that misuses its environment is called a Trojan horse.
     • Emulates another program E.g. a login screen which captures the user's login credentials
     • Another variation on the Trojan horse is spyware
       • First, a user may run with more privileges than necessary
       • Second, an operating system may allow by default more privileges than a normal user needs.
   • 15.2.2 Trap Door
     • The designer of a program or system might leave a hole in the software, which circumvents security
   • 15.2.3 Logic Bomb
     • a program that initiates a security incident only under certain circumstances.
   • 15.2.4 Stack and Buffer Overflow
     • The stack- or buffer-overflow attack is the most common way for an attacker outside the system
     • Essentially, the attack exploits a bug in a program. The bug can be a simple case of poor programming, in which the programmer neglected to code bounds checking on an input field.
     • the attacker sends more data than the program was expecting.
     • 1. Overflow an input field, command-line argument, or input buffer—for example, on a network daemon—until it writes into the stack. 2. Overwrite the current return address on the stack with the address of the exploit code loaded in step 3. 3. Write a simple set of code for the next space in the stack that includes the commands that the attacker wishes to execute—for instance, spawn a shell.
     • When a function is invoked in a typical computer architecture, the variables defined locally to the function (sometimes known as automatic variables), the parameters passed to the function, and the address to which control returns once the function exits are stored in a stack frame.
     • a cracker could execute a bufferoverflow attack. Her goal is to replace the return address in the stack frame so that it now points to the code segment containing the attacking program.
   • 15.2.5 Viruses
     • A virus is a fragment of code embedded in a legitimate program. Viruses are self-replicating and are designed to “infect” other programs.

5. 15.3 System and Network Threats

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