Category Archives: Systems

Security, Systems

Configuración de un Directorio SFTP en Chroot

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En algún momento, es posible que te encuentres en una situación en la que necesites otorgar acceso SFTP a un usuario, pero debe configurarse para evitar que naveguen por toda la estructura de directorios del sistema. Aquí es donde resulta útil la funcionalidad de chroot incorporada en sshd. Esto te permitirá restringir y aislar al usuario en un directorio específico y evitar fácilmente el acceso no autorizado. En este ejemplo, cubriremos los pasos de configuración para establecer el acceso para un usuario llamado Rafael en el departamento de contabilidad.

1. Crear el Usuario

Como usuario root, crea la cuenta y la contraseña para Rafael. Especificaremos el directorio de inicio como /var/contabilidad. Este será el directorio chroot que vamos a configurar. La shell debe ser /bin/false para evitar inicios de sesión interactivos.

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Security, Systems

Setting Up a Chrooted SFTP Directory

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At some point you might find yourself in a situation where you need to grant sftp access to a user but it should be configured to prevent them from traversing the entire directory structure within the system. This is where the built-in chroot functionality within sshd comes in handy. It will enable you to restrict and isolate the user to a specific directory and easily prevent unauthorized access. In this example, we will cover the configuration steps for setting up access for one user named jsmith within the Accounting department.

1. Create the User

As the root user, create the account & password for jsmith. We will specify the home directory as /var/accounting. This will be the chrooted directory we are going to setup. The shell should be /bin/false to prevent any interactive shell logins.

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Security, Systems

Certificate Transparency Logs

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Due to the ever increasing list of network compromises, securing our online presence has become more crucial than ever. One way to ensure online security is to use SSL/TLS certificates, which encrypt data transmissions between servers and clients, making them unreadable to any third-party. However, these certificates can be compromised, causing severe security breaches. This was seen back in 2011 with certificate authorities Comodo & DigiNotar. Read more here. There have been around 10 CA compromises in the last 3 – 4 years. Still a rare issue but one that needs consideration. That is where Certificate Transparency comes in, which is an open framework for monitoring SSL/TLS certificates.

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Networks, Systems

Fiber Factoids, Part 1 – A primer on common fiber optic cable types

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If you’ve been in the IT industry for any amount of time you are likely to have ran across fiber optic patch cables in use in various different installations. Typically, you will most often see fiber optic cables used for an uplink to an internet service provider, in between network devices between buildings in a campus network, or in a datacenter where large amounts of bandwidth and high speeds are required.

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Systems

Basic DHCP Setup

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Introduction

When it comes to efficiently assigning IP addresses to multiple clients, DHCP is the de facto standard in most networks. In this post, we’ll explore DHCP configuration on Red Hat Enterprise Linux 7 and give an example of how to install it, as well as a few configuration options for dhcpd. With a basic understanding of DHCP, you can get your network up and running almost immediately.

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Security, Systems

AIDE – File Integrity Monitoring

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The idea of using file integrity monitoring to validate your operating system and applications has been around since the late ’90s, with programs like Tripwire. Today, we have a steady stream of companies offering their own version for FIM. However, one consistent and reliable open source solution for Linux is AIDE or the Advanced Intrusion Detection Environment.

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Quick Tips, Systems

Configuring snmpv3 in Linux

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We have all used snmp for many years to help monitor our systems and networks but most admins have been reluctant to migrate to v3 due to the perceived increase in complexity. This post will show you how to quickly and easily enable snmpv3 on your linux system to take advantage of the additional security features to support authentication and privacy.

Install software packages

# yum install net-snmp net-snmp-utils
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Labs, Systems

Linux Lab – Access Control Lists

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Overview

As you know, Linux has a standard set of file access settings based on the concept of read, write, and execute permissions that determine who may access the file or directory in question. The most common way to set and change these permissions is to use commands like chmod, chown or chgrp. While these are powerful commands and have their place, there are occasions where it may be advantageous to fine tune the access to a file or directory. This is where file access control lists or FACLS come in.

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