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XCCDF
Guide to the Secure Configuration of Ubuntu 18.04
Introduction
General Principles
General Principles
An XCCDF Group - A logical subset of the XCCDF Benchmark
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General Principles
The following general principles motivate much of the advice in this guide and should also influence any configuration decisions that are not explicitly covered.
Encrypt Transmitted Data Whenever Possible
Data transmitted over a network, whether wired or wireless, is susceptible to passive monitoring. Whenever practical solutions for encrypting such data exist, they should be applied. Even if data is expected to be transmitted only over a local network, it should still be encrypted. Encrypting authentication data, such as passwords, is particularly important. Networks of Ubuntu 18.04 machines can and should be configured so that no unencrypted authentication data is ever transmitted between machines.
Least Privilege
Grant the least privilege necessary for user accounts and software to perform tasks. For example,
sudo
can be implemented to limit authorization to super user accounts on the system only to designated personnel. Another example is to limit logins on server systems to only those administrators who need to log into them in order to perform administration tasks. Using SELinux also follows the principle of least privilege: SELinux policy can confine software to perform only actions on the system that are specifically allowed. This can be far more restrictive than the actions permissible by the traditional Unix permissions model.
Minimize Software to Minimize Vulnerability
The simplest way to avoid vulnerabilities in software is to avoid installing that software. On Ubuntu 18.04,the Package Manager (originally
apt
), allows for careful management of the set of software packages installed on a system. Installed software contributes to system vulnerability in several ways. Packages that include setuid programs may provide local attackers a potential path to privilege escalation. Packages that include network services may give this opportunity to network-based attackers. Packages that include programs which are predictably executed by local users (e.g. after graphical login) may provide opportunities for trojan horses or other attack code to be run undetected. The number of software packages installed on a system can almost always be significantly pruned to include only the software for which there is an environmental or operational need.
Run Different Network Services on Separate Systems
Whenever possible, a server should be dedicated to serving exactly one network service. This limits the number of other services that can be compromised in the event that an attacker is able to successfully exploit a software flaw in one network service.
Configure Security Tools to Improve System Robustness
Several tools exist which can be effectively used to improve a system's resistance to and detection of unknown attacks. These tools can improve robustness against attack at the cost of relatively little configuration effort. In particular, this guide recommends and discusses the use of host-based firewalling, SELinux for protection against vulnerable services, and a logging and auditing infrastructure for detection of problems.