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

Preventing Theft

Computer theft—especially laptop theft—is a growing problem for businesses and individuals alike. The loss of a computer system can be merely annoying or can be an expensive ordeal. But if the computer contains information that is irreplaceable or extraordinarily sensitive, it can be devastating.

Fortunately, by following a small number of simple and inexpensive measures, you can dramatically reduce the chance that your laptop or desktop computer will be stolen.

Understanding Computer Theft

People steal computer systems for a wide variety of reasons. Many computer systems are stolen for resale—either the complete system or, in the case of sophisticated thieves, the individual components, which are harder to trace. Other computers are stolen by people who cannot afford to purchase their own computers. Still others are stolen for the information that they contain, usually by people who wish to obtain the information but sometimes by those who simply wish to deprive the computer’s owner of the use of the information. No matter why a computer is stolen, most computer thefts have one common element: opportunity. In most cases, computers are stolen because they have been left unprotected.

Laptops and Portable Computers

Laptops and other kinds of portable computers present a special hazard. They are easily stolen, difficult to tie down (they then cease to be portable!), and easily resold. Personnel with laptops should be trained to be especially vigilant in protecting their computers. In particular, theft of laptops in airports has been reported to be a major problem.

One way to minimize laptop theft is to make the laptops harder to resell. You can do this by engraving a laptop with your name and telephone number. (Do not engrave the laptop with your Social Security number, as this will enable a thief to cause you other problems!) See Section 8.3.2.2 for additional suggestions.

Laptop theft may not be motivated by resale potential. Often, competitive intelligence is more easily obtained by stealing a laptop with critical information than by hacking into a protected network. Thus, good encryption on a portable computer is critical.

Locks

One good way to protect your computer from theft is to physically secure it. A variety of physical tie-down devices are available to bolt computers to tables or cabinets. Although they cannot prevent theft, they make it more difficult.

Mobility is one of the great selling points of laptops. It is also the key feature that leads to laptop theft. One of the best ways to decrease the chance of having your laptop stolen is to lock it, at least temporarily, to a desk, a pipe, or another large object.

Most laptops sold today are equipped with a security slot (see Figure 8-1). For less than $50 you can purchase a cable lock that attaches to a nearby object and locks into the security slot. Once set, the lock cannot be removed without either using the key or damaging the laptop case, which makes it very difficult to resell the laptop. These locks prevent most grab-and-run laptop thefts. One of the largest suppliers of laptop locks is Kensington, which holds several key patents, although Kryptonite now makes a line of laptop locks as well.

Most laptops today are sold with a security slot (reprinted with permission of Kensington)

Figure 8-1. Most laptops today are sold with a security slot (reprinted with permission of Kensington)

Tagging

Another way to decrease the chance of theft for resale and increase the likelihood of return is to tag your computer equipment with permanent or semipermanent equipment tags. Tags work because it is illegal to knowingly buy or sell stolen property—the tags make it very difficult for potential buyers or sellers to claim that they didn’t know that the computer was stolen.

The best equipment tags are clearly visible and individually serial-numbered so that an organization can track its property. A low-cost tagging system is manufactured by Secure Tracking of Office Property (http://www.stoptheft.com) (see Figure 8-2). These tags are individually serial-numbered and come with a three-year tracking service. If a piece of equipment with a STOP tag is found, the company can arrange to have it sent by overnight delivery back to the original owner. An 800 number on the tag makes returning the property easy.

The STOP tag is a simple and effective way to label your laptop (reprinted with permission)

Figure 8-2. The STOP tag is a simple and effective way to label your laptop (reprinted with permission)

According to the company, many reports of laptop “theft” in airports are actually cases in which a harried traveler accidentally leaves a laptop at a chair or table when they are running for a flight (or in an airport bar after a long wait for a flight).[97] The STOP tag makes it easier for airport personnel to return the laptop than to keep it.

STOP tags are affixed to the laptop’s case with a special adhesive that is rated for 800 pounds if properly applied. Underneath the tag is a tattoo that will embed itself in plastic cases. Should the tag be removed, the words “Stolen Property” and STOP’s 800-number remain visible.

STOP tags are used by many universities, businesses, and the U.S. government. No laptop should be without one.

Laptop Recovery Software and Services

Several companies now sell PC “tracing” programs. The tracing program hides in several locations on a laptop and places a call to the tracing service on a regular basis to reveal its location. The calls can be made using either a telephone line or an IP connection. Normally these “calls home” are ignored, but if the laptop is reported stolen to the tracing service, the police are notified about the location of the stolen property.

Laptop recovery software works quite well, but it typically cannot survive a complete reformat of the computer’s hard disk. Of course, as few thieves actually reformat the hard disks of computers that they steal, this usually isn’t a problem.

Absolute Software Corporation’s Computrace (http://www.computrace.com) tracking system costs under $60 and requires a PC running DOS or Windows. Similar systems have yet to appear for Unix machines.

Of course, many of these systems work on desktop systems as well as laptops. Thus, you can protect systems that you believe have a heightened risk of being stolen.

RAM Theft

At times when RAM has been expensive, businesses and universities have suffered a rash of RAM thefts. Thieves enter offices, open computers, and remove some or all of the computer’s RAM (see Figure 8-3). Many computer businesses and universities have also had major thefts of advanced processor chips. RAM and late-model CPU chips are easily sold on the open market. They are virtually untraceable. And, when thieves steal only some of the RAM inside a computer, weeks or months may pass before the theft is noticed.

There are many cases of theft of all or part of computer RAM

Figure 8-3. There are many cases of theft of all or part of computer RAM

When the market is right, high-density RAM modules and processor cards can be worth their weight in gold. If a user complains that a computer is suddenly running more slowly than it did the day before, check its RAM, and then check to see that its case is physically secured.

Encryption

If your computer is stolen, the information it contains will be at the mercy of the equipment’s new “owners.” They may erase it or they may read it. Sensitive information can be sold, used for blackmail, or used to compromise other computer systems.

You can never make something impossible to steal. But you can make stolen information virtually useless—provided that it is encrypted and the thief does not know the encryption key. For this reason, even with the best computer security mechanisms and physical deterrents, sensitive information should be encrypted using an encryption system that is difficult to break. We recommend that you acquire and use a strong encryption system so that even if your computer is stolen, the sensitive information it contains will not be compromised. Chapter 7 contains detailed information on encryption.



[97] There is some anecdotal evidence that forgetful travelers find it easier to report to management that their laptop was stolen than to admit that they forgot it!