Operating System Security - Integrated Computer Security - Lecture Slides, Slides of Computer Security

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Lecture 18

Operating System Security

Operating System

• An OS allows different users to access

different resources in a shared way

• The OS needs to control

• the sharing and
• provide an interface to allow the access
  • Identification and authentication are required for access control

Separation

• Keep one user's objects separate from other users
• Physical separation
  • Use different physical resources for different users
  • Easy to implement, but expensive and inefficient
• Temporal separation
  • Execute different users' programs at different times
• Logical separation
  • User is given the impression that no other users exist
  • As done by an operating system
• Cryptographic separation
  • Encrypt data and make it unintelligible to outsiders
  • Complex

Sharing

• Sometimes, users want to share resources
  • Library routines (e.g., libc)
  • Files or database records
• OS should allow flexible sharing , not “all or nothing”
  • Which files or records?
    • Which part of a file/record?
  • Which other users?
    • Can other users share objects further?
  • What uses are permitted?
    • Read but not write, view but not print (feasibility?)
    • Aggregate information only
  • For how long?

Measures

• the 2010 Australian Defense Signals Directorate (DSD)

list the “ Top 35 Mitigation Strategies ”

• over 70% of the targeted cyber intrusions investigated by DSD in 2009 could have been prevented
• the top four measures for prevention are:
• patch operating systems and applications using auto-update
• patch third-party applications
• restrict admin privileges to users who need them
• white-list approved applications

Operating System Security

• possible for a system to be compromised during the

installation process

• before it can install the latest patches
  • building and deploying a system should be a planned process designed to counter this threat
• process must:
• assess risks and plan the system deployment
• secure the underlying operating system and then the key applications
• ensure any critical content is secured
• ensure appropriate network protection mechanisms are used
• ensure appropriate processes are used to maintain security

NIST System Security Planning

• the purpose of the system, the type of information stored, the applications and services provided, and their security requirements
• the categories of users of the system, the privileges they have, and the types of information they can access
• how the users are authenticated
• how access to the information stored on the system is managed
• what access the system has to information stored on other hosts, such as file or database servers, and how this is managed
• who will administer the system, and how they will manage the system (via local or remote access)
• any additional security measures required on the system, including the use of host firewalls, anti-virus or other malware protection mechanisms, and logging

OPERATING SYSTEM HARDENING

Initial Setup and Patching

• system security begins with the installation of the OS
  • ideally new systems should be constructed on a protected network
  • full installation and hardening process should occur before the system is deployed to its intended location
• initial installation should install the minimum necessary for the desired system
• overall boot process must also be secured
• the integrity and source of any additional device driver code must be carefully validated
• critical that the system be kept up to date, with all critical security related patches installed - should stage and validate all patches on the test systems before deploying them in production

Remove Unnecessary Services, Applications, Protocols

• if fewer software packages are available to run the risk is reduced - system planning process should identify what is actually required for a given system
• when performing the initial installation the supplied defaults should not be used - default configuration is set to maximize ease of use and functionality rather than security - if additional packages are needed later they can be installed when they are required
• not installing unwanted software
  • many uninstall scripts fail to completely remove all components
  • disabled service might be enabled by an attacker who got in

Configure Resource Controls

• once the users and groups are defined,

appropriate permissions can be set on data

and resources

• many of the security hardening guides provide

lists of recommended changes to the default

access configuration

Install Additional Security Controls

• further security possible by installing and

configuring additional security tools:

• anti-virus software
• host-based firewalls
• IDS or IPS software
• application white-listing

APPLICATION SECURITY

Application Configuration

• may include:
  • creating and specifying appropriate data storage areas for application
  • making appropriate changes to the application or service default configuration details
• some applications or services may include:
  • default data, scripts, user accounts
• of particular concern with remotely accessed

services such as Web and file transfer services

• risk from this form of attack is reduced by ensuring that most of the files can only be read by the server