Complete Referance of Hardening in Linux Security

• System Hardening Overview
• Batille
• Securing X-Windows
• Securing Linux Daemons
• Security patches
• Security Benchmarks

System Hardening Overview

• Linux, like other operatingsystems, is not secure “out of the box”
• Security increases as newer versions and distros come out
• Users/administrators still need to take steps to “harden” systems
• Items typically requiring securing/hardening include:
• X-Windows
• System daemons
• Networking services

Bastille

• Scripts walk SA through several modules, automates changing a large number of configurable system items
• Has modules for checking and configuring Internet services, suid(set-user-ID) files, account and boot security, and TCP wrappers
• Bastille program is available from http://bastille-linux.sourceforge.net/
• Bastille currently supports most distros of Linux and Unix including:
• Red Hat, SuSe, Debian, Gentoo, Mandrake, and HP-UX

Securing X-Windows

• X-windows is Graphical Interface for Linux
• Comes with most distributions,but is ot part of them
• Used to access systems both locally and remotely
• X is a Protocol and set of utilities
• Client-server design
• Runs from the X server, and provides keyboard, mouse and video
• Not configured securely by default
• Signals can get intercepted btween x-server and client(either remote or local)
• Several ways of securing X
• xhost – controls authentication to x erver on a host basis
• X server maintains lists of allowed hosts
• xhost allows hosts to be added/deleted from list
• Vulnerabilities: Host spoofing, sessions are per host, not per user
• xauth – controls authentication through .Xauthority
• .Xauthority file contains authentication ‘cookie’ that client must send to server
• Best security mechanism is using X windows over ssh
• Authentication can be controlled and audited through user credentials
• communications traffic between x client and X erver is encrypted

Securing Linux Daemons

• Daemons are same as Windows services
• Programs that run in background to accomplish system tasks
• Often run with a set of credentials and privilege levels
• Securing Linux Daemons is to not install unnecessary ones!.
• Best way to secure daemons is to not install unnessary ones!
• Don’t use “Install Everything” option during installation
• Install services according to machine role
• Use ‘ps’ and ‘netstat’ commands to determine what services are running and network connections established by them
• Many Daemons turned on/off in /etc/inetd.conf – edit this file to selectively disable services that are not needed
• Recompiling kernel is another way to secure services
• Generate learner kernel with only daemons you need supported
• Eliminates risk of daemons being reconfigured or restarted

Security Patches

• Even after initial hardening, Linux can still be insecure
• New vulnerabilities discovered every day
• Security patches issued to counter threats and fix vulnerabilities
• Most current distros have automated patch utility
• Connects to trusted centralized site and downloads latest patches
• Usually provides patches for OS and popular software apps included in distro
• Third party apps frequently need patches from different vendors
• Usually manual download and installation process
• Download patches only from trusted sites
• Verify hashes provided with patches to ensure file integrity
• Many utilities to download and install security patches
• Up2date, YUM, and YaST are a few
• Get familiar with your distro’s update utilities

Security Benchmarks

• Several free and commercial tools exist to test/measure security on Linux
• Benchmarks available for almost all distros
• Usually automated tool that checks security of daemons, processes, accounts,permissions , etc.
• Nessus is free valnerability scanner provided with most distros
• Uses frequently updated database of vulnerabilities
• Can be used for single or multiple machines
• Uses client/server architecture

Rajesh Kumar

I’m a DevOps/SRE/DevSecOps/Cloud Expert passionate about sharing knowledge and experiences. I have worked at Cotocus. I share tech blog at DevOps School, travel stories at Holiday Landmark, stock market tips at Stocks Mantra, health and fitness guidance at My Medic Plus, product reviews at TrueReviewNow , and SEO strategies at Wizbrand.

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