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Applies to SUSE Linux Enterprise Server 12 SP3

About This Guide

The SUSE Linux Enterprise Server Security and Hardening Guide deals with the particulars of installation and set up of a secure SUSE Linux Enterprise Server and additional post-install processes required to further secure and harden that installation. Security and hardening elements and procedures are best applied to a server both during installation and post-installation and aim to improve the fitness of the system for the purposes demanded by its administrator.

This guide supports administrator in making security related choices and decisions. The individual steps and procedures should be seen as proposals, not as strict rules. You will often need to evaluate the usefulness of measures for your organization yourself.

The objective is to improve the security value of the system. Definitions about the meaning of the term security vary, but we want to settle on one that is both simple and abstract:

A good system does what it is expected to do, and it does it well.

A secure system is a good system that does nothing else.

The focus of this guide lies on doing nothing else. The Linux system is constructed in such way that security policies are enforced. These policies consist of the following concepts (fairly generic and incomplete list):

  • DAC (Discretionary Access Control): File and directory permissions, as set by chmod and chown.

  • Privileged ports: TCP and UDP ports 0-1023 and raw sockets can only be used by root.

  • Other privileged operations: Loading kernel modules, configuring network interfaces, all security relevant settings of the Linux kernel. These are operations that can only be done by the root user, that is the user with the user ID 0, or any other process with the necessary capabilities.

Attacking a system means to attempt to overcome privilege boundaries, for example by circumventing or breaking them. That means the administrator or programmer of the system has not anticipated this scenario.

A hardened system raises the bar by reducing the area that the system exposes to the attacker (often called attack surface). A hardened system can also provide measures to reduce the impact of vulnerabilities in the parts of the systems that must be exposed to a potential attacker.

Security is about decisions, and whenever security is in (apparent) opposition to function, these decisions become trade-offs. While it can be argued that all systems should be set up to be as securely as possible, some levels of security and hardening may very well be overkill in some cases. Each system's operational environment has its own security requirements derived from business drivers or regulatory compliance mandates. SUSE Linux Enterprise Server can, for example, be configured to comply with security standards, such as SOX, HIPAA and PCIDSS. It can also be set up to fulfill the requirements from the German Federal Office of Information Security (Bundesamt für Sicherheit in der Informationstechnik) as described in BSI TR-02102-1. An effective business requirements analysis should be performed to determine the right level of security and hardening to be applied to a server or defined as part of a baseline server build.

As a final note before we begin: You may encounter individual requirements in regulatory compliance frameworks that may not make sense from a technical perspective, or they do not serve the purpose of improving security. It may be a productive attitude to simply implement what is required, but whenever there is a contradiction to security, an informed discussion in the documentation serves the overall purpose of your regulative compliance framework much more than blindly obeying the specifications. Feel encouraged to dispute list items that you think are counterproductive.

1 Assumptions and Scope

References in this document will usually be made to a single server target or host, however the scope can generally be applied to more than one machine. We generally assume that the security target can cover one or more systems running SUSE Linux Enterprise Server.

We explicitly do not make any assumptions about the hostility of the network that the systems are connected to, or the cooperative nature of the users that leverage the services provided by the systems.

In turn, this means that you partially define your context on your own when reading through this document. You will need to broaden the meaning of individual portions to adapt it to your environment. In some cases, such as the use case of a server that is exposed to the Internet, this document may even be insufficient or incomplete; however, it may still serve as a good starting point on your journey toward an increased level of confidence that your system will behave like you want it to.

About trust: Trust relationships exist among all systems that participate in networked transactions. In this way, the trust relationship between the people that use the systems is transported across these systems. The chain that is formed by your trust relationships is only as strong as the weakest link. It is good practice to graphically visualize the trust relationships with the services in a schematic overview or map of your network. Generally, it is up to the owner of a resource to enforce the policies imposed on that resource; this would usually be the server that provides the resource. The client that opens a connection to request the resource can only be made responsible for the actions that it performs. This refers to the action of opening the connection to start with, but to nothing else as such.

The case of hostile users is special and unique: The Human Resources department may be able to solve some security problems in your computing environment; in addition, some technical measures can be taken. Make sure that the necessary regulations in your environment fit your needs, and that they back your intentions instead of obstructing them if you need to work around a missing support from your HR department (and your management).

Persons that have administrative privileges on a system are automatically considered trusted.

A Linux system—without any additional security frameworks such as SELinux—is a single level security system: From a security policy perspective there is only the superuser (root) and non-privileged users. System users are non-root user IDs that have access to files specific to their purpose. The separation of administrative duties is complicated by this simplicity. Some tools help: Use sudo(8) for administrative tasks, but be aware that after the privilege boundary is crossed, a program running with root privileges does not enforce any file access policies for non-privileged users anymore. vi(1) that runs as root can read and write to any file in the system.

Another tool to mitigate the risk of abuse or accidental misuse of administrative privileges is NetIQ's Privileged User Manager product. More information is available here:

Physical security of the server is another assumption made here, where the server is protected from theft and manipulation by unauthorized persons. A common sobering thought among security professionals is the ten-second Denial of Service: Unplug the wires and reboot the server. Physical security must be ensured and physical access must be controlled. Otherwise, all assumptions about at least the availability of these systems are void.

Note
Note: Cryptography

The use of cryptography to protect the confidentiality of transactions with the services that your system provides is generally encouraged. The need to implement cryptographic enhancements is strongly dependent on the operational environments of all participating systems. Keep in mind that you need to verify all of the possible security benefits that cryptography can provide, for all of your services, and that these benefits are not delivered automatically by turning on the encrypt option of your service (if you can enjoy the idyllic situation where encryption is available as a button to check):

Confidentiality

Protection against reading the content of a transaction

Privacy

Protection against knowing that a transaction exists, and some properties that it may have, such as size, identities of involved parties, their presence, etc.

Integrity

Protection against alteration of content. Be aware that cryptography does not automatically provide this kind of protection.

Authenticity

Protection against identity fraud. Cryptography that does not know about identities of participating entities cannot deliver this value.

Keep in mind that encryption of data for confidentiality purposes can merely reduce the size of the data to protect from the actual size to the size of the key that is used to encrypt the data. This results in a key exchange problem for encrypted transactions, and in a key management problem for encrypted data storage. Since data is (typically, there are exceptions!) processed in clear, you need your vault unlocked while data within is being worked with. The encryption of such data on the file system or block device layer helps against the theft of the system, but it does not help the confidentiality of the data while the system is running.

If you want to implement a consistent security policy covering multiple hosts on a network then organizational procedures must ensure that all those hosts can be trusted and are configured with compatible security configurations enforcing an organization wide security policy. Isolation of groups of systems that maintain data of the same trust domain can provide an adequate means of control; ultimately, the access controls to these systems, both for end users and for other systems, need to be carefully designed, configured, inspected and monitored.

Important
Important: Trusting Data

Data can only be trusted to the degree that is associated with the domain it comes from. If data leaves the domain in which security policies can be enforced, it should consequently be associated with the trust of the target domain.

For a review of industry best practices on security, the development of sound security processes, controls, development, reviews, audit practices and incident management, you can review a public RFC (request for comments). RFC 2196 is the ongoing work of the world-wide community and individual security and process experts. You can review it online here: http://www.faqs.org/rfcs/rfc2196.html. An RFC is an open and living document that invites comments and review. Enhancements and improvements are welcome; you will find instructions on where to send those suggestions within the document itself.

This guide provides initial guidance on how to set up and secure a SUSE Linux Enterprise Server installation but it is not intended to be the only information required for a system administrator to learn how to operate Linux securely. Assumptions are made within this guide that the reader has knowledge and understanding of operating security principles in general, and of Linux administrative commands and configuration options in particular.

2 Contents of this Book

Part I, “Common Criteria” contains a reference to Common Criteria and SUSE Linux Enterprise Server. Part II, “General System Security and Service Protection Methods” contains more general system security and service protection schemes.

3 Documentación disponible

Disponemos de versiones en HTML y PDF de nuestros libros en distintos idiomas. Para este producto están disponibles los siguientes manuales destinados a usuarios y administradores:

Guía de inicio rápido de la instalación

Presenta los requisitos del sistema y proporciona instrucciones detalladas para instalar SUSE Linux Enterprise Server desde un DVD o una imagen ISO.

Guía de distribución

Muestra cómo instalar uno o varios sistemas y cómo aprovechar las posibilidades del producto para una infraestructura de distribución. Puede optar entre varios enfoques: desde una instalación local o un servidor de instalación en red, hasta una distribución masiva usando una técnica de instalación automatizada, altamente personalizada y controlada de forma remota.

Administration Guide

Trata sobre las tareas de administración del sistema, como el mantenimiento, la supervisión y la personalización de un sistema ya instalado.

Virtualization Guide

Describe la tecnología de virtualización en general y presenta libvirt, la interfaz unificada para la virtualización, y muestra información detallada sobre algunos hipervisores.

Storage Administration Guide

Ofrece información sobre la gestión de los dispositivos de almacenamiento de un servidor SUSE Linux Enterprise Server.

AutoYaST

AutoYaST es un sistema que permite instalar uno o varios sistemas SUSE Linux Enterprise Server automáticamente sin intervención del usuario, mediante un perfil de AutoYaST que contiene datos de instalación y de configuración. El manual le guiará a través de los pasos básicos de la instalación automática: preparación, instalación y configuración.

Security Guide

Presenta conceptos básicos sobre la seguridad del sistema, tanto a nivel local como de red. Muestra cómo usar el software de seguridad inherente del producto, como AppArmor o el sistema de auditoría que recopila de forma fiable información sobre los eventos de seguridad relevantes.

Security and Hardening Guide

Describe los aspectos concretos relacionados con la instalación y configuración de un entorno SUSE Linux Enterprise Server seguro, así como los procesos adicionales posteriores a la instalación para proteger y reforzar aún más su seguridad. Ayuda al administrador con las elecciones y decisiones relacionadas con la seguridad.

System Analysis and Tuning Guide

Se trata de una guía de administración para la detección de posibles problemas, su resolución y la optimización del sistema. Encontrará información sobre cómo inspeccionar y optimizar el sistema mediante herramientas de supervisión y sobre la gestión eficaz de los recursos. También contiene una descripción general de problemas habituales y su solución, así como ayuda adicional y recursos de documentación.

SMT Guide

Una guía del administrador de la Herramienta de gestión de suscripciones, un sistema proxy para el Centro de servicios al cliente de SUSE con los destinos de repositorio y de registro. Obtenga información sobre cómo instalar y configurar un servidor SMT local, cómo duplicar y gestionar repositorios, cómo gestionar los equipos cliente y cómo configurar clientes para el uso de SMT.

GNOME User Guide

Presenta el escritorio GNOME de SUSE Linux Enterprise Server. Le guiará a través del uso y la configuración del escritorio y le permitirá llevar a cabo tareas esenciales. Su contenido está dirigido a usuarios que quieran usar GNOME de forma más eficiente como escritorio por defecto.

Encontrará las versiones en formato HTML de la mayoría de los manuales de productos en el sistema instalado en /usr/share/doc/manual. Las últimas actualizaciones de la documentación están disponibles en http://www.suse.com/documentation/, donde puede descargar la documentación para el producto en varios formatos.

4 Comentarios

Existen varios canales disponibles para hacernos llegar los comentarios:

Errores y peticiones de mejoras

Para obtener más información sobre los servicios y las opciones de asistencia técnica disponibles para el producto, consulte http://www.suse.com/support/.

Para informar sobre errores en un componente del producto, diríjase a https://scc.suse.com/support/requests, entre a la sesión y haga clic en Create New (Crear nuevo).

Comentarios del usuario

Nos gustaría recibir sus comentarios o sugerencias acerca de este manual y del resto de la documentación incluida junto con el producto. Utilice la función de comentarios del usuario, situada en la parte inferior de las páginas de la documentación en línea, o bien diríjase a http://www.suse.com/documentation/feedback.html e introduzca ahí sus comentarios.

Mail

Para hacernos llegar comentarios sobre la documentación del producto, también puede enviar un mensaje de correo a doc-team@suse.com. No olvide incluir el título del documento, la versión del producto y la fecha de publicación de la documentación. Para informar de errores o sugerir mejoras, proporcione una descripción concisa del problema y haga referencia a la sección y página (o URL) en concreto donde lo ha encontrado.

5 Convenciones de la documentación

En esta documentación se utilizan los siguientes avisos y convenciones tipográficas:

  • /etc/passwd: nombres de directorio y nombres de archivos

  • ESPACIO RESERVADO: sustituya ESPACIO RESERVADO con el valor real

  • PATH: variable de entorno PATH

  • ls, --help: comandos, opciones y parámetros

  • usuario: usuarios o grupos

  • nombre del paquete: el nombre de un paquete

  • Alt, AltF1: tecla o combinación de teclas que se deben pulsar; las teclas se muestran en mayúsculas, tal y como aparecen en el teclado

  • Archivo, Archivo › Guardar como: elementos de menú, botones_

  • AMD/Intel Este párrafo solo es relevante para la arquitectura AMD64/Intel 64. Las flechas marcan el principio y el final del bloque de texto.

    IBM Z, POWER Este párrafo solo es relevante para las arquitecturas z Systems y POWER. Las flechas marcan el principio y el final del bloque de texto.

  • Pingüinos que bailan (Capítulo Pingüinos, ↑Otro manual): referencia a un capítulo de otro manual.

  • Comandos que se deben ejecutar con privilegios de usuario root. A menudo, también es posible añadir estos comandos como prefijos con el comando sudo para que un usuario sin privilegios los puedan ejecutar.

    root # command
    tux > sudo command
  • Comandos que pueden ejecutar los usuarios sin privilegios.

    tux > command
  • Notificaciones

    Warning
    Warning: aviso de advertencia

    Información vital que debe tener en cuenta antes de continuar. Advierte acerca de problemas de seguridad, pérdida de datos potenciales, daños del hardware o peligros físicos.

    Important
    Important: aviso importante

    Información importante que debe tener en cuenta antes de continuar.

    Note
    Note: aviso de nota

    Información adicional, por ejemplo sobre las diferencias en las versiones de software.

    Tip
    Tip: aviso de sugerencia

    Información útil, como una directriz o un consejo práctico.

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