Fighting dictionary attacks with Sshutout and Fail2ban
Protection against DoS
SSH has two jails: the one just mentioned and sshd-ddos. This jail is not designed to prevent attempts to guess passwords, but to counter denial-of-service (DoS) attacks that open connections to the SSH daemon without entering a password.The logfile contains messages like this in case of a DoS attack:
sshd: Did not receive identification string from 10.0.0.150
Although you could configure multiple regular expressions per jail, many admins will prefer to assign different ban times for distributed DoS (DDoS) attacks as opposed to failed login attempts. That is, splitting this into the SSH and sshd-ddos categories makes a lot of sense.
The SSH jail is the only one set to enabled = true by default; all other jails – including sshd-ddos – have to be enabled manually.
Protection Scheme
If a user enters the wrong password multiple times, the results are similar to the Sshutout results: An iptables rule is triggered and locks out all connections from the offending computer for the next five minutes (Figure 2).
Protection for other services follows the same pattern (Figure 3). If you have a number of login-protected web pages on your Apache web server, Fail2ban will give you a jail to match,
[apache] enabled = false port = http,https filter = apache-auth logpath = /var/log/apache*/*access.log maxretry = 3
which you need to modify slightly. The Apache version that I run writes error messages to a separate error.log file, and not to access.log. After setting enabled = true, you can enable the jail.
Tip: A more elegant approach than simply restarting the Fail2ban daemon, which could mean disabling active iptables rules, is to send the following command from the Fail2ban client to the server:
fail2ban-client start apache
This command tells the server to add the [apache] entry to the list of active jails. To try this out, I entered a number of invalid passwords, and a new iptables rule was activated.
Infos
- Sshutout: http://www.techfinesse.com/sshutout/sshutout.html
- Fail2ban: http://www.fail2ban.org
« Previous 1 2
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Fedora Asahi 40 Remix Available for Macs with Apple Silicon
If you've been anticipating KDE's Plasma 6 for your Apple Silicon-powered Mac, then you're in luck.
-
Red Hat Adds New Deployment Option for Enterprise Linux Platforms
Red Hat has re-imagined enterprise Linux for an AI future with Image Mode.
-
OSJH and LPI Release 2024 Open Source Pros Job Survey Results
See what open source professionals look for in a new role.
-
Proton 9.0-1 Released to Improve Gaming with Steam
The latest release of Proton 9 adds several improvements and fixes an issue that has been problematic for Linux users.
-
So Long Neofetch and Thanks for the Info
Today is a day that every Linux user who enjoys bragging about their system(s) will mourn, as Neofetch has come to an end.
-
Ubuntu 24.04 Comes with a “Flaw"
If you're thinking you might want to upgrade from your current Ubuntu release to the latest, there's something you might want to consider before doing so.
-
Canonical Releases Ubuntu 24.04
After a brief pause because of the XZ vulnerability, Ubuntu 24.04 is now available for install.
-
Linux Servers Targeted by Akira Ransomware
A group of bad actors who have already extorted $42 million have their sights set on the Linux platform.
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.