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Security and Hardening Guide
SUSE Linux Enterprise Server 15 SP2

Security and Hardening Guide

Introduces basic concepts of system security, covering both local and network security aspects. Shows how to use the product inherent security software like AppArmor, SELinux, or the auditing system that reliably collects information about any security-relevant events. Supports the administrator with security-related choices and decisions in installing and setting up a secure SUSE Linux Enterprise Server and additional processes to further secure and harden that installation.

Publication Date: October 15, 2021
About This Guide
Available Documentation
Giving Feedback
Documentation Conventions
Product Life Cycle and Support
1 Security and Confidentiality
1.1 Overview
1.2 Passwords
1.3 System Integrity
1.4 File Access
1.5 Networking
1.6 Software Vulnerabilities
1.7 Malware
1.8 Important Security Tips
1.9 Reporting Security Issues
2 Common Criteria
2.1 Introduction
2.2 Evaluation Assurance Level (EAL)
2.3 Generic Guiding Principles
2.4 For More Information
I Authentication
3 Authentication with PAM
3.1 What is PAM?
3.2 Structure of a PAM Configuration File
3.3 The PAM Configuration of sshd
3.4 Configuration of PAM Modules
3.5 Configuring PAM Using pam-config
3.6 Manually Configuring PAM
3.7 For More Information
4 Using NIS
4.1 Configuring NIS Servers
4.2 Configuring NIS Clients
5 Setting Up Authentication Clients Using YaST
5.1 Configuring an Authentication Client with YaST
5.2 SSSD
6 LDAP with 389 Directory Server
6.1 Structure of an LDAP directory tree
6.2 Installing 389 Directory Server
6.3 Firewall configuration
6.4 Backing up and restoring 389 Directory Server
6.5 Managing LDAP users and groups
6.6 Setting up SSSD
6.7 Managing modules
6.8 Importing TLS server certificates and keys
6.9 More information
7 Network Authentication with Kerberos
7.1 Conceptual Overview
7.2 Kerberos Terminology
7.3 How Kerberos Works
7.4 User View of Kerberos
7.5 Installing and Administering Kerberos
7.6 Setting up Kerberos using LDAP and Kerberos Client
7.7 Kerberos and NFS
7.8 For More Information
8 Active Directory Support
8.1 Integrating Linux and Active Directory Environments
8.2 Background Information for Linux Active Directory Support
8.3 Configuring a Linux Client for Active Directory
8.4 Logging In to an Active Directory Domain
8.5 Changing Passwords
9 Setting Up a FreeRADIUS Server
9.1 Installation and Testing on SUSE Linux Enterprise
II Local Security
10 Physical Security
10.1 System Locks
10.2 Locking Down the BIOS
10.3 Security via the Boot Loaders
10.4 Retiring Linux Servers with Sensitive Data
10.5 Restricting Access to Removable Media
11 Automatic Security Checks with seccheck
11.1 Seccheck Timers
11.2 Enabling Seccheck Timers
11.3 Daily, Weekly, and Monthly Checks
11.4 Automatic Logout
12 Software Management
12.1 Removing Unnecessary Software Packages (RPMs)
12.2 Patching Linux Systems
13 File Management
13.1 Disk Partitions
13.2 Checking File Permissions and Ownership
13.3 Default umask
13.4 SUID/SGID Files
13.5 World-Writable Files
13.6 Orphaned or Unowned Files
14 Encrypting Partitions and Files
14.1 Setting Up an Encrypted File System with YaST
14.2 Encrypting Files with GPG
15 Storage Encryption for Hosted Applications with cryptctl
15.1 Setting Up a cryptctl Server
15.2 Setting Up a cryptctl Client
15.3 Checking Partition Unlock Status Using Server-side Commands
15.4 Unlocking Encrypted Partitions Manually
15.5 Maintenance Downtime Procedure
15.6 For More Information
16 User Management
16.1 Various Account Checks
16.2 Enabling Password Aging
16.3 Stronger Password Enforcement
16.4 Password and Login Management with PAM
16.5 Restricting root Logins
16.6 Restricting sudo Users
16.7 Setting an Inactivity Timeout for Interactive Shell Sessions
16.8 Preventing Accidental Denial of Service
16.9 Displaying Login Banners
16.10 Connection Accounting Utilities
17 Spectre/Meltdown Checker
17.1 Using spectre-meltdown-checker
17.2 Additional Information about Spectre/Meltdown
18 Configuring Security Settings with YaST
18.1 Security Overview
18.2 Predefined Security Configurations
18.3 Password Settings
18.4 Boot Settings
18.5 Login Settings
18.6 User Addition
18.7 Miscellaneous Settings
19 Authorization with PolKit
19.1 Conceptual Overview
19.2 Authorization Types
19.3 Querying Privileges
19.4 Modifying Configuration Files
19.5 Restoring the Default Privileges
20 Access Control Lists in Linux
20.1 Traditional File Permissions
20.2 Advantages of ACLs
20.3 Definitions
20.4 Handling ACLs
20.5 ACL Support in Applications
20.6 For More Information
21 Certificate Store
21.1 Activating Certificate Store
21.2 Importing Certificates
22 Intrusion Detection with AIDE
22.1 Why Use AIDE?
22.2 Setting Up an AIDE Database
22.3 Local AIDE Checks
22.4 System Independent Checking
22.5 For More Information
III Network Security
23 X Window System and X Authentication
24 SSH: Secure Network Operations
24.1 ssh—Secure Shell
24.2 scp—Secure Copy
24.3 sftp—Secure File Transfer
24.4 The SSH Daemon (sshd)
24.5 SSH Authentication Mechanisms
24.6 Port Forwarding
24.7 Adding and Removing Public Keys on an Installed System
24.8 For More Information
25 Masquerading and Firewalls
25.1 Packet Filtering with iptables
25.2 Masquerading Basics
25.3 Firewalling Basics
25.4 firewalld
25.5 Migrating from SuSEfirewall2
25.6 For More Information
26 Configuring a VPN Server
26.1 Conceptual Overview
26.2 Setting Up a Simple Test Scenario
26.3 Setting Up Your VPN Server Using a Certificate Authority
26.4 Setting Up a VPN Server or Client Using YaST
26.5 For More Information
27 Enabling FIPS 140-2
27.1 Enabling FIPS
IV Confining Privileges with AppArmor
28 Introducing AppArmor
28.1 AppArmor Components
28.2 Background Information on AppArmor Profiling
29 Getting Started
29.1 Installing AppArmor
29.2 Enabling and Disabling AppArmor
29.3 Choosing Applications to Profile
29.4 Building and Modifying Profiles
29.5 Updating Your Profiles
30 Immunizing Programs
30.1 Introducing the AppArmor Framework
30.2 Determining Programs to Immunize
30.3 Immunizing cron Jobs
30.4 Immunizing Network Applications
31 Profile Components and Syntax
31.1 Breaking an AppArmor Profile into Its Parts
31.2 Profile Types
31.3 Include Statements
31.4 Capability Entries (POSIX.1e)
31.5 Network Access Control
31.6 Profile Names, Flags, Paths, and Globbing
31.7 File Permission Access Modes
31.8 Mount Rules
31.9 Pivot Root Rules
31.10 PTrace Rules
31.11 Signal Rules
31.12 Execute Modes
31.13 Resource Limit Control
31.14 Auditing Rules
32 AppArmor Profile Repositories
33 Building and Managing Profiles with YaST
33.1 Manually Adding a Profile
33.2 Editing Profiles
33.3 Deleting a Profile
33.4 Managing AppArmor
34 Building Profiles from the Command Line
34.1 Checking the AppArmor Status
34.2 Building AppArmor Profiles
34.3 Adding or Creating an AppArmor Profile
34.4 Editing an AppArmor Profile
34.5 Unloading Unknown AppArmor Profiles
34.6 Deleting an AppArmor Profile
34.7 Two Methods of Profiling
34.8 Important File Names and Directories
35 Profiling Your Web Applications Using ChangeHat
35.1 Configuring Apache for mod_apparmor
35.2 Managing ChangeHat-Aware Applications
36 Confining Users with pam_apparmor
37 Managing Profiled Applications
37.1 Reacting to Security Event Rejections
37.2 Maintaining Your Security Profiles
38 Support
38.1 Updating AppArmor Online
38.2 Using the Man Pages
38.3 For More Information
38.4 Troubleshooting
38.5 Reporting Bugs for AppArmor
39 AppArmor Glossary
V SELinux
40 Configuring SELinux
40.1 Why use SELinux?
40.2 SELinux policy overview
40.3 Installing SELinux packages
40.4 Installing an SELinux policy
40.5 Modifying the GRUB 2 bootloader
40.6 Configuring SELinux
40.7 Managing SELinux
40.8 Troubleshooting
VI The Linux Audit Framework
41 Understanding Linux Audit
41.1 Introducing the Components of Linux Audit
41.2 Configuring the Audit Daemon
41.3 Controlling the Audit System Using auditctl
41.4 Passing Parameters to the Audit System
41.5 Understanding the Audit Logs and Generating Reports
41.6 Querying the Audit Daemon Logs with ausearch
41.7 Analyzing Processes with autrace
41.8 Visualizing Audit Data
41.9 Relaying Audit Event Notifications
42 Setting Up the Linux Audit Framework
42.1 Determining the Components to Audit
42.2 Configuring the Audit Daemon
42.3 Enabling Audit for System Calls
42.4 Setting Up Audit Rules
42.5 Configuring Audit Reports
42.6 Configuring Log Visualization
43 Introducing an Audit Rule Set
43.1 Adding Basic Audit Configuration Parameters
43.2 Adding Watches on Audit Log Files and Configuration Files
43.3 Monitoring File System Objects
43.4 Monitoring Security Configuration Files and Databases
43.5 Monitoring Miscellaneous System Calls
43.6 Filtering System Call Arguments
43.7 Managing Audit Event Records Using Keys
44 Useful Resources
A Achieving PCI DSS Compliance
A.1 What Is the PCI DSS?
A.2 Focus of This Document: Areas Relevant to the Operating System
A.3 Requirements in Detail
B GNU Licenses
B.1 GNU Free Documentation License
List of Examples
3.1 PAM Configuration for sshd (/etc/pam.d/sshd)
3.2 Default Configuration for the auth Section (common-auth)
3.3 Default Configuration for the account Section (common-account)
3.4 Default Configuration for the password Section (common-password)
3.5 Default Configuration for the session Section (common-session)
3.6 pam_env.conf
6.1 Excerpt from CN=schema
6.2 Minimal 389 Directory Server instance configuration file
6.3 A .dsrc file for local administration
7.1 Example KDC Configuration, /etc/krb5.conf
25.1 Callback Port Configuration for the nfs Kernel Module in /etc/modprobe.d/60-nfs.conf
25.2 Commands to Define a new firewalld RPC Service for NFS
26.1 VPN Server Configuration File
26.2 VPN Client Configuration File
29.1 Output of aa-unconfined
34.1 Learning Mode Exception: Controlling Access to Specific Resources
34.2 Learning Mode Exception: Defining Permissions for an Entry
40.1 Security context settings using ls -Z
40.2 Verifying that SELinux is functional
40.3 Getting a list of booleans and verifying policy access
40.4 Getting file context information
40.5 The default context for directories in the root directory
40.6 Showing SELinux settings for processes with ps Zaux
40.7 Viewing default file contexts
40.8 Example lines from /etc/audit/audit.log
40.9 Analyzing audit messages
40.10 Viewing which lines deny access
40.11 Creating a policy module allowing an action previously denied
41.1 Example output of auditctl -s
41.2 Example Audit Rules—Audit System Parameters
41.3 Example Audit Rules—File System Auditing
41.4 Example Audit Rules—System Call Auditing
41.5 Deleting Audit Rules and Events
41.6 Listing Rules with auditctl -l
41.7 A simple audit event—viewing the audit log
41.8 An Advanced Audit Event—Login via SSH
41.9 Example /etc/audisp/audispd.conf
41.10 Example /etc/audisp/plugins.d/syslog.conf

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