Linux Security HOWTO

Kevin Fenzi, kevin@scrye.com & Dave Wreski, dave@nic.com

1. Introduction

• 1.1 New Versions of this Document
• 1.2 Feedback
• 1.3 Disclaimer
• 1.4 Copyright Information

2. Overview

• 2.1 Why Do We Need Security?
• 2.2 How Secure Is Secure?
• 2.3 What Are You Trying to Protect?
• 2.4 Developing A Security Policy
• 2.5 Means of Securing Your Site
• 2.6 Organization of This Document

3. Physical Security

• 3.1 Computer locks
• 3.2 BIOS Security
• 3.3 Boot Loader Security
• 3.4 xlock and vlock
• 3.5 Detecting Physical Security Compromises

4. Local Security

• 4.1 Creating New Accounts
• 4.2 Root Security

5. Files and Filesystem Security

• 5.1 Umask Settings
• 5.2 File Permissions
• 5.3 Integrity Checking with Tripwire Tripwire
• 5.4 Trojan Horses

6. Password Security and Encryption

• 6.1 PGP and Public-Key Cryptography
• 6.2 SSL, S-HTTP, HTTPS and S/MIME
• 6.3 Linux IPSEC Implementations
• 6.4 ssh (Secure Shell) and stelnet
• 6.5 PAM - Pluggable Authentication Modules
• 6.6 Cryptographic IP Encapsulation (CIPE)
• 6.7 Kerberos
• 6.8 Shadow Passwords.
• 6.9 "Crack" and "John the Ripper"
• 6.10 CFS - Cryptographic File System and TCFS - Transparent Cryptographic File System
• 6.11 X11, SVGA and display security

7. Kernel Security

• 7.1 2.0 Kernel Compile Options
• 7.2 2.2 Kernel Compile Options
• 7.3 Kernel Devices

8. Network Security

• 8.1 Packet Sniffers
• 8.2 System services and tcp_wrappers
• 8.3 Verify Your DNS Information
• 8.4 identd
• 8.5 SATAN, ISS, and Other Network Scanners
• 8.6 sendmail, qmail and MTA's
• 8.7 Denial of Service Attacks
• 8.8 NFS (Network File System) Security.
• 8.9 NIS (Network Information Service) (formerly YP).
• 8.10 Firewalls
• 8.11 IP Chains - Linux Kernel 2.2.x Firewalling
• 8.12 VPN's - Virtual Private Networks

9. Security Preparation (before you go on-line)

• 9.1 Make a Full Backup of Your Machine
• 9.2 Choosing a Good Backup Schedule
• 9.3 Backup Your RPM or Debian File Database
• 9.4 Keep Track of Your System Accounting Data
• 9.5 Apply All New System Updates.

10. What To Do During and After a Breakin

• 10.1 Security Compromise Underway.
• 10.2 Security Compromise has already happened

11. Security Sources

• 11.1 FTP Sites
• 11.2 Web Sites
• 11.3 Mailing Lists
• 11.4 Books - Printed Reading Material

12. Glossary

13. Frequently Asked Questions

14. Conclusion

15. Acknowledgements