Linux / Unix Security

The latest in-depth reviews, guides, news, howtos and other information on IT security, Linux, open source, firewalls, networks, privacy, encryption, cryptography, attacks, vulnerabilities, and much more ( rss feed ).


All supported versions of FreeBSD are affected by various security bugs that need to be applied ASAP. If the process is privileged, it may escape jail and gain full access to the FreeBSD system. Similarly, when using Xen, a malicious or buggy frontend driver may be able to cause resource leaks. Let us see what and how to fix these security vulnerabilities on FreeBSD.
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On Linux, we encrypt our partitions and entire disk using Linux Unified Key Setup-on-disk-format (LUKS) for security and privacy reasons. We unlock LUKS protected disk by providing a passphrase at boot time. You need to be in front of your computer or use a remote console to open the encrypted disk under Linux at boot time. However, if your system is in the basement, remote datacenter/office, or upstairs office, you won’t able to unlock and boot your Linux box. We can use the Dropbear SSH server for LUKS encrypted Debian or Ubuntu or any other Linux distro via SSH to solve this problem. Let us see how to unlock LUKS using Dropbear SSH keys in Linux at boot time.
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The last ten years in the computer and IT security world are crippled with so many vulnerabilities. We saw massive cloud computing adoption and end-users using mobile devices with high speed 4G LTE networks. A threat actor may have exploited such weakness in modern computers and networks. Let us look into top vulnerabilities and the attack surface in this decade (2010-2020) that affected Linux/Unix, macOS, IT, cloud-computing, and computers in general.
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We use encryption to protect mobile devices. For instance, I always use LUKS disk encryption to protect all files stored on my SSD. Dm-crypt (Cryptsetup and LUKS) open-source disk encryption is transparent disk encryption and a great way to keep your data secure. However, changing passphrase is a bit of a challenge for new Linux users and developers. This step-by-step guide explains how to find LUKS slots assigned to you and change your passphrase on a Debian/Ubuntu, CentOS/RHEL, OpenSUSE/SUSE other Linux distros.
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Let’s Encrypt is a non-profit certificate authority that provides X.509 certificates for Transport Layer Security (TLS) encryption free of cost. The TLS certificate is valid for 90 days only. However, Due to the bug, they need to revoke many (read as “certain”) Let’s Encrypt TLS/SSL certificates. Let us see how to find out if you are affected by this bug and how you can fix it to avoid any problems with your TLS/SSL certificates.
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FreeBSD is a free and open source operating system. The NFS (Network File System) is a server and client application that turn FreeBSD into a file sharing server. Users can upload or update files on a remote NFS server. NFS is standard on NAS (network attached storage) devices or sharing data for web servers. A new bug found in NFS server code which could allow a remote attacker to crash the NFS server, resulting in a denial of service (DoS) attack. Another possibility is to execute arbitrary code on the server.
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Exim is a free and open source message transfer agent (MTA) developed at the University of Cambridge. It is famous on Unix and Linux systems connected to the Internet. It is freely available under the terms of the GNU General Public Licence. There is a buffer overflow in base64d() of Exim MTA that allows an attacker to run code remotely. ALL versions of Exim MTA affected by overflow vulnerability i.e. CVE-2018-6789.
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OpenSSH needs no introduction. OpenSSH is a free and open source suite of security-related software based on the SSH protocol. OpenSSH provides secure network communication and tunneling capabilities. OpenSSH gives peace of mind when communicating with Linux or Unix-like server over the Internet on the insecure network.

SSH is essential for both sysadmins and developers. The book “SSH Mastery” (2nd ed) talks about OpenSSH server, clients, encryption, public/private keys, VPNs and other security-related network-level utilities based on the Secure Shell SSH protocol.
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