Enhancing Remote Access Security
Jump Box Security

While Linux can be made very secure, you can increase the security of your entire network with jump boxes.
Special Thanks: This article was made possible by support from Linux Professional Institute
A jump box is a system set up with multi-factor authentication (MFA) usually placed in a network DMZ with very restricted access to the corporate network and no returning Internet access for any protocol. In other words, the jump box has only one path in via SSH ,and no other protocols are allowed outbound to the Internet or into the corporate network. Figure 1 shows a simplified diagram of a jump box and where and how it is positioned within your network.
A secure jump box is an excellent out-of-band (OOB) remote access method for system administrators. It ensures that your network has 24x7x365 support and is a reasonable solution when some of your users either have no direct office or data center access.
Internet Access
The jump box should be set up with MFA, as should all systems attached to the corporate network. No user should be in the sudoers group or be allowed to become the root user on this system. When the jump box system requires maintenance, a system administrator should use a console login either via an onboard access controller or through a directly attached keyboard, video, and mouse (KVM) apparatus.
Since the jump box resides in the DMZ or another network that can be accessed via the Internet, great care should be taken to ensure its security by applying patches and updates as soon as they are made available. Additionally, the jump box shouldn’t host any protocols except for SSHD. The jump box has a single purpose as an SSH gateway into the corporate network. The only exception is for MFA purposes. Some MFA solutions require Internet access or at least some method of communicating with an authentication service inside the network. Time-based solutions are more secure, but any MFA solution is more secure than simple passwords alone.
MFA
It’s hard to stress the MFA requirement enough. No accounts on the jump box system should be accessible without using MFA unless it is a console login. The most secure type of MFA is to require that each user have a physical token such as a hardware token, which is a device that generates random numbers or alphanumeric sequences.
To use a hardware token, the user supplies a username, a passcode, and a random number or sequence from the token. The random number that is generated is usually only active for 60 seconds. This security principle is based on “something you know plus something you have” that a remote hacker couldn’t gain access to or spoof.
Additional Security
To further secure your jump servers, you should follow these suggestions:
- Disable or remove unnecessary protocols, daemons, and services.
- Never store SSH private keys on the jump server.
- Configure internal hosts with /etc/hosts.allow and /etc/hosts.deny files to control access.
- Create at least one secondary /backup jump box in case of failure.
- Use a restrictive, host-based firewall for all Linux systems.
- Set up a service such as Fail2Ban to resist brute-force attacks.
- Install a minimal distribution option.
- Set up NAT forwarding to your jump box.
Remember that there’s no such thing as too much security when it comes to protecting your data, your customer base, and your intellectual property. Internet-accessible systems will come under attack; they need to be secure, and convenience should never be a factor in selecting security measures.
Some network administrators also place a firewall between the Internet and the DMZ and use NAT port forwarding for all services. Leaving systems wide open on all protocols is not a good practice. It makes more sense to secure the DMZ by limiting the incoming and outgoing protocols from that network.
Buy Linux Magazine
Direct Download
Read full article as PDF:
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Find SysAdmin Jobs
News
-
The Next Major Release of Elementary OS Has Arrived
It's been over a year since the developers of elementary OS released version 6.1 (Jólnir) but they've finally made their latest release (Horus) available with a renewed focus on the user.
-
KDE Plasma 5.27 Beta Is Ready for Testing
The latest beta iteration of the KDE Plasma desktop is now available and includes some important additions and fixes.
-
Netrunner OS 23 Is Now Available
The latest version of this Linux distribution is now based on Debian Bullseye and is ready for installation and finally hits the KDE 5.20 branch of the desktop.
-
New Linux Distribution Built for Gamers
With a Gnome desktop that offers different layouts and a custom kernel, PikaOS is a great option for gamers of all types.
-
System76 Beefs Up Popular Pangolin Laptop
The darling of open-source-powered laptops and desktops will soon drop a new AMD Ryzen 7-powered version of their popular Pangolin laptop.
-
Nobara Project Is a Modified Version of Fedora with User-Friendly Fixes
If you're looking for a version of Fedora that includes third-party and proprietary packages, look no further than the Nobara Project.
-
Gnome 44 Now Has a Release Date
Gnome 44 will be officially released on March 22, 2023.
-
Nitrux 2.6 Available with Kernel 6.1 and a Major Change
The developers of Nitrux have officially released version 2.6 of their Linux distribution with plenty of new features to excite users.
-
Vanilla OS Initial Release Is Now Available
A stock GNOME experience with on-demand immutability finally sees its first production release.
-
Critical Linux Vulnerability Found to Impact SMB Servers
A Linux vulnerability with a CVSS score of 10 has been found to affect SMB servers and can lead to remote code execution.