If Ubuntu 24.04 has not fixed the packaged content, this may install the incompatible version.

To install the deb-package manually following steps are necessary for Ubuntu 24.04 (following the steps from How to install or upgrade fail2ban manually · fail2ban/fail2ban Wiki · GitHub. You may want to refer to the linked article for more details).

The following is an example for 1.1.0:

cd /tmp/
# 1) download deb package and signature:
wget -O fail2ban.deb https://github.com/fail2ban/fail2ban/releases/download/1.1.0/fail2ban_1.1.0-1.upstream1_all.deb
wget -O fail2ban.deb.asc https://github.com/fail2ban/fail2ban/releases/download/1.1.0/fail2ban_1.1.0-1.upstream1_all.deb.asc

# 2) check signature (if you want to be sure file is unmodified):
gpg --verify fail2ban.deb.asc fail2ban.deb

# 3) view details of the package:
dpkg -I fail2ban.deb

# 4) to ensure the upgrade run gentler (protocol of previous version may be incompatible), stop fail2ban before install:
# using service:
sudo service fail2ban stop

# 5a) install package using dpkg (standalone package, don't regard dependencies):
sudo dpkg -i fail2ban.deb
# if the package introduces some "broken" dependencies (I don't think so in case of fail2ban which has few dependencies),
# to fix the unmet dependency issue, run this:
sudo apt -f install

Now you should have the 1.1.0 version of Fail2Ban installed.

# Start the service:
sudo systemctl start fail2ban

# And check the status if the service is running well:
sudo systemctl status fail2ban

Now you should have the compatible 1.1.0 version of Fail2Ban running on your Ubuntu 24.04 LTS.

We also checked the alternative installation using (step 5b, see How to install or upgrade fail2ban manually · fail2ban/fail2ban Wiki · GitHub), but this requires gdebi. gdebi needs to be installed beforehand under Ubuntu 24.04 but we refrained as the tool and its dependencies would have been consumed additional 350 MB.

Source : https://www.airix.net/index.php?option=com_content&view=article&id=89:ubuntu-2404-with-fail2ban-issue-fix&catid=53:featured&Itemid=271