Access your servers securely with a Magic URL

Dance the Two-Step

Earlier I promised to show you how I integrated other security layers with my Magic URL. You briefly saw how I tidied up any fail2ban iptables rules for my dynamic IP address within the main script. Here, I will take a quick look at some two-step authentication configuration.

I will leave you to research the finer details of setting up your two-step verification with the excellent Google Authenticator. However, should you want to add functionality to your Magic URL, wherein IP addresses you know and trust don't have to run through the two-step code-entering process but instead are just asked for a password, then you can use code like this:

echo -e "+ : ALL :
+ : ALL : ${GSM}
- : ALL : ALL" > /etc/security/access-local.conf

As you can see, ${GSM} is the IP address extracted from the Magic URL functionality. If asked, I would say use this with caution and probably only allow fixed-line IP addresses to connect over SSH without running through the two-step process.

The End

Although this approach to opening up access is rudimentary in places, I would like to think it encourages sys admins to develop their lateral thinking. The fact that you can get htaccess to deal with unique IP addresses, rename the Magic URL every minute with a new timestamp derivative (or via another security token), and incorporate other failsafes into a security design raises many questions about how far it's possible to go in securing a server using relatively basic tools.

If you know that you won't be able to carry your SSH key with you for a period of time, you could take two-step authentication scratch codes with you on a piece of paper (or just switch off two-step completely) and still get SSH access relatively securely from anywhere on the planet using this approach.

Something else I might try in the future is spawning another type of task or application with a Magic URL. I didn't want a big clunky Submit button embedded within a web page to allow Magic URL functionality, but you could easily customize this approach to run any service or script you like.

Having read about the Magic URL I use for my CCTV server, I hope you will attempt some of these methods in a creative way to suit your own security needs.

The Author

Chris Binnie's new book, Linux Server Security: Hack and Defend [6], shows how hackers launch sophisticated attacks to compromise servers, steal data, and crack complex passwords, so you can learn how to defend against these attacks. In the book, he also talks you through making your servers invisible, performing penetration testing, and mitigating unwelcome attacks. You can find out more about Linux servers and security at his website (

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