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

Prelude

There are three major rules for handling security breaches:

  1. Don’t panic. No matter what has happened, you will only make things worse if you act without thinking.

  2. Document. Whether your goal is to get your system running again as soon as possible, or you want to collect evidence for a prosecution, you will be better off if you document what you do.

  3. Plan ahead. The key to effective response is advance planning. If you plan and practice your response to a security incident, you’ll be better equipped to handle the incident when and if it ever happens.

Rule #1: Don’t Panic

After a security breach, you are faced with many different choices. Should you shut down the computer, disconnect the network, or call the cops? No matter what has happened, you will only make things worse if you act without thinking.

Before acting, you need to answer certain questions and keep the answers firmly in mind:

  • Did you really have a breach of security? Something that appears to be the action of an intruder might actually be the result of human error or software failure.

  • Was any damage really done? With many security breaches, the perpetrator gains unauthorized access but doesn’t actually access privileged information or maliciously change the contents of files.

  • Is it important to obtain and protect evidence that might be used in an investigation?

  • Is it important to get the system back into normal operation as soon as possible?

  • Are you willing to take the chance that files have been altered or removed? If not, how can you tell for sure if changes have been made?

  • Does it matter if anyone within the organization hears about this incident? If somebody outside hears about it?

  • Is an insider suspected?

  • Do you know how the intruder got in?

  • Do you know how many systems are involved?

  • Can it happen again?

The answers to many of these questions may be contradictory; for example, protecting evidence and comparing files may not be possible if the goal is to get the system back into normal operation as soon as possible. You’ll have to decide what’s best for your own site.

Rule #2: Document

Start a paper log, immediately. Take a notebook and write down everything you find, always noting the date and time. If you examine text files, print copies and then sign and date the hardcopy. If you have the necessary disk space, record your entire session with the script command. Having this information on hand to study later may save you considerable time and aggravation, especially if you need to restore or change files quickly to bring the system back to normal.

This chapter and the chapters that follow present a set of guidelines for handling security breaches. In the following sections, we describe the mechanisms you can use to help you detect a break-in, and handle the question of what to do if you discover an intruder on your system. In Chapter 24 we’ll describe denial of service attacks; ways in which attackers can make your system unusable without actually destroying any information. In Chapter 25 we’ll discuss legal approaches and other issues you may need to consider after a security incident.

Rule #3: Plan Ahead

A key to effective response in an emergency is advance planning. When a security problem occurs, there are some standard steps to be taken. You should have these steps planned out in advance so there is little confusion or hesitation when an incident occurs.

In larger installations, you may want to practice your plans. For example, along with standard fire drills, you may want to have “virus drills” to practice coping with the threat of a virus, or “break-in drills” to practice techniques for preserving evidence and re-establishing normal operations.

The following basic steps should be at the heart of your plan:

Step 1: Identify and understand the problem

If you don’t know what the problem is, you cannot take action against it. This rule does not mean that you need to have perfect understanding, but you should understand at least what form of problem you are dealing with. Cutting your organization’s Internet connection won’t help you if the problem is being caused by a vengeful employee with a laptop who is hiding out in a co-worker’s office.

Step 2: Contain or stop the damage

If you’ve identified the problem, take immediate steps to halt or limit it. For instance, if you’ve identified the employee who is deleting system files, you should turn off his account, and probably take disciplinary action as well. Both are steps to limit the damage to your data and system.

Step 3: Confirm your diagnosis and determine the damage

After you’ve taken steps to contain the damage, confirm your diagnosis of the problem and determine the damage it caused. Are files still disappearing after the employee has been discharged? You may never be 100% sure if two or more incidents are actually related. Furthermore, you may not be able to identify all of the damage immediately, if ever.

Step 4: Preserve the evidence, if necessary

If you intend to prosecute or seek legal redress for your incident, you must make an effort to preserve necessary evidence before going further. Failure to preserve evidence does not prohibit you from calling the cops or filing a suit against the suspected perpetrator, but the lack of evidence may significantly decrease your chances for success. Be advised: preserving evidence can take time and is hard to do properly. For this reason, many organizations dealing with incidents forgo this step.

Step 5: Restore your system

After you know the extent of the damage, you need to restore the system and data to a consistent state. This may involve reloading portions of the system from backups, or it may mean a simple restart of the system. Before you proceed, be certain that all of the programs you are going to use are “safe.” The attacker may have replaced your restore program with a Trojan horse that deletes both the files on your hard disk and on your backup tape!

Step 6: Deal with the cause

If the problem occurred because of some weakness in your security or operational measures, you should make changes and repairs after your system has been restored to a normal state. If the cause was a person making a mistake, you should probably educate her to avoid a second occurrence of the situation. If someone purposefully interfered with your operations, you may wish to involve law enforcement authorities.

Step 7: Perform related recovery

If what occurred was covered by insurance, you may need to file claims. Rumor control, and perhaps even community relations, will be required at the end of the incident to explain what happened, what breaches occurred, and what measures were taken to resolve the situation. This step is especially important with a large user community because unchecked rumors and fears can often damage your operations more than the problem itself.

Step 8: Postmortem

Once the heat has died down, review the incident and your handling of it. How could you and your team have handled the situation better? What effort was wasted? What wrong decisions were made? How could you have prevented it from happening in the first place?

In addition to having a plan of action, you can be prepared by creating a toolkit on read-only media (floppy, CD-ROM, etc.). This toolkit will give you a set of programs for incident response that you know are not compromised. Include programs that you will need to examine a compromised system, such as: awk, bash, cat, compress, cut, dd, des, df, du, file, find, grep, gzip, icat, ifconfig, last, ls, lsmod, lsof, md5sum, modinfo, more, netcat, netstat, nmap, paste, pcat, Perl, PGP, pkginfo, ps, rpm, rm, script, sed, strings, strace, tar, top, Tripwire, truss, uncompress, vi, and w. Don’t forget shared libraries (or ensure that the programs are statically linked). Having a bootable live filesystem on your CD or DVD is useful as well.