Table of Contents for
Practical UNIX and Internet Security, 3rd Edition

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Practical UNIX and Internet Security, 3rd Edition by Alan Schwartz Published by O'Reilly Media, Inc., 2003
  1. Cover
  2. Practical Unix & Internet Security, 3rd Edition
  3. A Note Regarding Supplemental Files
  4. Preface
  5. Unix “Security”?
  6. Scope of This Book
  7. Which Unix System?
  8. Conventions Used in This Book
  9. Comments and Questions
  10. Acknowledgments
  11. A Note to Would-Be Attackers
  12. I. Computer Security Basics
  13. 1. Introduction: Some Fundamental Questions
  14. What Is Computer Security?
  15. What Is an Operating System?
  16. What Is a Deployment Environment?
  17. Summary
  18. 2. Unix History and Lineage
  19. History of Unix
  20. Security and Unix
  21. Role of This Book
  22. Summary
  23. 3. Policies and Guidelines
  24. Planning Your Security Needs
  25. Risk Assessment
  26. Cost-Benefit Analysis and Best Practices
  27. Policy
  28. Compliance Audits
  29. Outsourcing Options
  30. The Problem with Security Through Obscurity
  31. Summary
  32. II. Security Building Blocks
  33. 4. Users, Passwords, and Authentication
  34. Logging in with Usernames and Passwords
  35. The Care and Feeding of Passwords
  36. How Unix Implements Passwords
  37. Network Account and Authorization Systems
  38. Pluggable Authentication Modules (PAM)
  39. Summary
  40. 5. Users, Groups, and the Superuser
  41. Users and Groups
  42. The Superuser (root)
  43. The su Command: Changing Who You Claim to Be
  44. Restrictions on the Superuser
  45. Summary
  46. 6. Filesystems and Security
  47. Understanding Filesystems
  48. File Attributes and Permissions
  49. chmod: Changing a File’s Permissions
  50. The umask
  51. SUID and SGID
  52. Device Files
  53. Changing a File’s Owner or Group
  54. Summary
  55. 7. Cryptography Basics
  56. Understanding Cryptography
  57. Symmetric Key Algorithms
  58. Public Key Algorithms
  59. Message Digest Functions
  60. Summary
  61. 8. Physical Security for Servers
  62. Planning for the Forgotten Threats
  63. Protecting Computer Hardware
  64. Preventing Theft
  65. Protecting Your Data
  66. Story: A Failed Site Inspection
  67. Summary
  68. 9. Personnel Security
  69. Background Checks
  70. On the Job
  71. Departure
  72. Other People
  73. Summary
  74. III. Network and Internet Security
  75. 10. Modems and Dialup Security
  76. Modems: Theory of Operation
  77. Modems and Security
  78. Modems and Unix
  79. Additional Security for Modems
  80. Summary
  81. 11. TCP/IP Networks
  82. Networking
  83. IP: The Internet Protocol
  84. IP Security
  85. Summary
  86. 12. Securing TCP and UDP Services
  87. Understanding Unix Internet Servers and Services
  88. Controlling Access to Servers
  89. Primary Unix Network Services
  90. Managing Services Securely
  91. Putting It All Together: An Example
  92. Summary
  93. 13. Sun RPC
  94. Remote Procedure Call (RPC)
  95. Secure RPC (AUTH_DES)
  96. Summary
  97. 14. Network-Based Authentication Systems
  98. Sun’s Network Information Service (NIS)
  99. Sun’s NIS+
  100. Kerberos
  101. LDAP
  102. Other Network Authentication Systems
  103. Summary
  104. 15. Network Filesystems
  105. Understanding NFS
  106. Server-Side NFS Security
  107. Client-Side NFS Security
  108. Improving NFS Security
  109. Some Last Comments on NFS
  110. Understanding SMB
  111. Summary
  112. 16. Secure Programming Techniques
  113. One Bug Can Ruin Your Whole Day . . .
  114. Tips on Avoiding Security-Related Bugs
  115. Tips on Writing Network Programs
  116. Tips on Writing SUID/SGID Programs
  117. Using chroot( )
  118. Tips on Using Passwords
  119. Tips on Generating Random Numbers
  120. Summary
  121. IV. Secure Operations
  122. 17. Keeping Up to Date
  123. Software Management Systems
  124. Updating System Software
  125. Summary
  126. 18. Backups
  127. Why Make Backups?
  128. Backing Up System Files
  129. Software for Backups
  130. Summary
  131. 19. Defending Accounts
  132. Dangerous Accounts
  133. Monitoring File Format
  134. Restricting Logins
  135. Managing Dormant Accounts
  136. Protecting the root Account
  137. One-Time Passwords
  138. Administrative Techniques for Conventional Passwords
  139. Intrusion Detection Systems
  140. Summary
  141. 20. Integrity Management
  142. The Need for Integrity
  143. Protecting Integrity
  144. Detecting Changes After the Fact
  145. Integrity-Checking Tools
  146. Summary
  147. 21. Auditing, Logging, and Forensics
  148. Unix Log File Utilities
  149. Process Accounting: The acct/pacct File
  150. Program-Specific Log Files
  151. Designing a Site-Wide Log Policy
  152. Handwritten Logs
  153. Managing Log Files
  154. Unix Forensics
  155. Summary
  156. V. Handling Security Incidents
  157. 22. Discovering a Break-in
  158. Prelude
  159. Discovering an Intruder
  160. Cleaning Up After the Intruder
  161. Case Studies
  162. Summary
  163. 23. Protecting Against Programmed Threats
  164. Programmed Threats: Definitions
  165. Damage
  166. Authors
  167. Entry
  168. Protecting Yourself
  169. Preventing Attacks
  170. Summary
  171. 24. Denial of Service Attacks and Solutions
  172. Types of Attacks
  173. Destructive Attacks
  174. Overload Attacks
  175. Network Denial of Service Attacks
  176. Summary
  177. 25. Computer Crime
  178. Your Legal Options After a Break-in
  179. Criminal Hazards
  180. Criminal Subject Matter
  181. Summary
  182. 26. Who Do You Trust?
  183. Can You Trust Your Computer?
  184. Can You Trust Your Suppliers?
  185. Can You Trust People?
  186. Summary
  187. VI. Appendixes
  188. A. Unix Security Checklist
  189. Preface
  190. Chapter 1: Introduction: Some Fundamental Questions
  191. Chapter 2: Unix History and Lineage
  192. Chapter 3: Policies and Guidelines
  193. Chapter 4: Users, Passwords, and Authentication
  194. Chapter 5: Users, Groups, and the Superuser
  195. Chapter 6: Filesystems and Security
  196. Chapter 7: Cryptography Basics
  197. Chapter 8: Physical Security for Servers
  198. Chapter 9: Personnel Security
  199. Chapter 10: Modems and Dialup Security
  200. Chapter 11: TCP/IP Networks
  201. Chapter 12: Securing TCP and UDP Services
  202. Chapter 13: Sun RPC
  203. Chapter 14: Network-Based Authentication Systems
  204. Chapter 15: Network Filesystems
  205. Chapter 16: Secure Programming Techniques
  206. Chapter 17: Keeping Up to Date
  207. Chapter 18: Backups
  208. Chapter 19: Defending Accounts
  209. Chapter 20: Integrity Management
  210. Chapter 21: Auditing, Logging, and Forensics
  211. Chapter 22: Discovering a Break-In
  212. Chapter 23: Protecting Against Programmed Threats
  213. Chapter 24: Denial of Service Attacks and Solutions
  214. Chapter 25: Computer Crime
  215. Chapter 26: Who Do You Trust?
  216. Appendix A: Unix Security Checklist
  217. Appendix B: Unix Processes
  218. Appendixes C, D, and E: Paper Sources, Electronic Sources, and Organizations
  219. B. Unix Processes
  220. About Processes
  221. Signals
  222. Controlling and Examining Processes
  223. Starting Up Unix and Logging In
  224. C. Paper Sources
  225. Unix Security References
  226. Other Computer References
  227. D. Electronic Resources
  228. Mailing Lists
  229. Web Sites
  230. Usenet Groups
  231. Software Resources
  232. E. Organizations
  233. Professional Organizations
  234. U.S. Government Organizations
  235. Emergency Response Organizations
  236. Index
  237. Index
  238. Index
  239. Index
  240. Index
  241. Index
  242. Index
  243. Index
  244. Index
  245. Index
  246. Index
  247. Index
  248. Index
  249. Index
  250. Index
  251. Index
  252. Index
  253. Index
  254. Index
  255. Index
  256. Index
  257. Index
  258. Index
  259. Index
  260. Index
  261. Index
  262. Index
  263. About the Authors
  264. Colophon
  265. Copyright

On the Job

Your security concerns with an employee should not stop after that person is hired.

Initial Training

Every potential computer user should undergo fundamental education in security policy as a matter of course. At the least, this education should include procedures for password selection and use, physical access to computers and networks (who is authorized to connect equipment, and how), backup procedures, dial-in policies, and policies for divulging information over the telephone. Executives should not be excluded from these classes because of their status—they are as likely (or more likely) as other personnel to pick poor passwords and commit other errors. They, too, must demonstrate their commitment to security: security consciousness flows from the top down, not the other way.

Education should include written materials and a copy of the computer-use policy. The education should include discussion of appropriate and inappropriate use of the computers and networks, personal use of computing equipment (during and after hours), policies on ownership and use of electronic mail, and policies on import and export of software and data. Penalties for violations of these policies should also be detailed.

All users should sign a form acknowledging the receipt of this information, and their acceptance of its restrictions. These forms should be retained. Later, if any question arises as to whether the employee was given prior warning about what was allowed, there will be proof.

Ongoing Training and Awareness

Periodically, users should be presented with refresher information about security and appropriate use of the computers. This retraining is an opportunity to explain good practice, remind users of current threats and their consequences, and provide a forum to air questions and concerns.

Your staff should also be given adequate opportunities for ongoing training. This training should include support to attend professional conferences and seminars, subscribe to professional and trade periodicals, and obtain reference books and other training materials. Your staff must also be given sufficient time to make use of the material, and positive incentives to master it.

Coupled with periodic education, you may wish to employ various methods of continuing awareness. These methods could include putting up posters or notices about good practice,[100] having periodic messages of the day with tips and reminders, having an “Awareness Day” every few months, or having other events to keep security from fading into the background.

Of course, the nature of your organization, the level of threat and possible loss, and the size and nature of your user population should all be factored into your plans. The cost of awareness activities should also be considered and budgeted in advance.

Performance Reviews and Monitoring

The performance of your staff should be reviewed periodically. In particular, the staff should be given credit and rewarded for professional growth and good practice. At the same time, problems should be identified and addressed in a constructive manner. You must encourage staff members to increase their abilities and enhance their understanding.

You should also avoid creating situations in which staff members feel overworked, underappreciated, or ignored. Creating such a working environment can lead to carelessness and a lack of interest in protecting the interests of the organization. The staff could also leave for better opportunities. Or worse, the staff could become involved in acts of disruption as a matter of revenge. Overtime must be an exception and not the rule, and all employees—especially those in critical positions—must be given adequate holiday and vacation time. Overworked, chronically tired employees are more likely to make mistakes, overlook problems, and become emotionally fragile. They also tend to suffer stress in their personal lives—families and loved ones might like to see them occasionally. Overstressed, overworked employees are likely to become disgruntled, and that does not advance the cause of good security.

In general, users with privileges should be monitored for signs of excessive stress, personal problems, or other indications of difficulties. Identifying such problems and providing help, where possible, is at the very least humane. Such practice is also a way to preserve valuable resources: the users themselves, and the resources to which they have access.

A user under considerable financial or personal stress might spontaneously take some action that he would never consider in more normal situations—and that action might be damaging to your operations, to your personnel, and to the employee himself. When we read in the newspaper about someone who goes on a shooting spree in the office, who cleans out the corporate bank account, or who commits suicide, the coworkers almost always comment about how they knew he was stressed or acting funny. Too bad they didn’t act to help head it off.

Managers should watch for employees who are obviously stressed; have trouble interacting with some other workers, customers, or vendors; have financial or health problems; have repeated problems with inappropriate use of computing resources (e.g., they are drawn to porn or gambling sites); or have other obvious troubles. Guiding them to counseling is a compassionate and humane thing to do, even if the behavior is severe enough to warrant termination. Most communities have low-cost or free services if other services are not covered under your company’s benefits plan.

Auditing Access

Ensure that auditing of access to equipment and data is enabled, and is monitored. Furthermore, ensure that anyone with such access knows that auditing is enabled. Many instances of computer abuse are spontaneous in nature. If a possible malefactor knows that the activity and access are logged, he might be discouraged in his actions.

Audit is not only done via the computer. Logs of people entering and leaving the building, electronic lock audit trails, and closed-circuit TV tapes all provide some accountability.

At the same time, we caution against routine, surreptitious monitoring. People do not like the idea that they might not be trusted and could be covertly watched. If they discover that they are, in fact, being watched, they may become very angry and may even take extreme action. In some venues, labor laws and employment contracts can result in the employer’s facing large civil judgments.

Simply notifying employees they are being monitored is not sufficient if the monitoring is too comprehensive. Some studies have shown that employees actually misbehave more and are less productive when they are monitored too extensively. This is true whether you are monitoring how often they take coffee breaks, timing every phone call, or keeping a record of every web site visited.

The best policies are those that are formulated with the input of the employees themselves, and with personnel from your human resources department (if you have one).

Least Privilege and Separation of Duties

Consider carefully the time-tested principles of least privilege and separation of duties. These should be employed wherever practical in your operations.

Least privilege

This principle states that you give each person the minimum access necessary to do her job. This restricted access is both logical (access to accounts, networks, programs) and physical (access to computers, backup tapes, and other peripherals). If every user has accounts on every system and has physical access to everything, then all users are roughly equivalent in their level of threat.

Separation of duties

This principle states that you should carefully separate duties so that people involved in checking for inappropriate use are not also capable of contributing to such inappropriate use. Thus, having all the security functions and audit responsibilities reside with the same person is dangerous. This practice can lead to a case in which the person violates security policy and commit prohibited acts, yet no other person sees the audit trail or is alerted to the problem.



[100] If you do this, change them periodically. A poster or notice that has not changed in many months becomes invisible.