Comment 7 for bug 2055114

As of this commit from 12 Dec 2023: https://github.com/fail2ban/fail2ban/commit/1024452fe1befeb5a0a014386a81ec183cd45bb5
....upstream ships its source with the missing async* libraries embedded, which solves the issue for now.

Here is a suggested workaround for Noble until the fix hopefully finds its way into the repos.

DISCLAMER: Try at your own risk. I am not an Ubuntu/Debian developer. Next time you receive a proper package update of fail2ban via apt, any of the manually-downloaded files below may cause conflicts and break your system.

mkdir -m 0755 /usr/lib/python3/dist-packages/fail2ban/compat
wget -O /usr/lib/python3/dist-packages/fail2ban/compat/asynchat.py https://github.com/fail2ban/fail2ban/raw/1024452fe1befeb5a0a014386a81ec183cd45bb5/fail2ban/compat/asynchat.py
wget -O /usr/lib/python3/dist-packages/fail2ban/compat/asyncore.py https://github.com/fail2ban/fail2ban/raw/1024452fe1befeb5a0a014386a81ec183cd45bb5/fail2ban/compat/asyncore.py
cp -p /usr/lib/python3/dist-packages/fail2ban/server/asyncserver.py{,.original}
wget -O /usr/lib/python3/dist-packages/fail2ban/server/asyncserver.py https://github.com/fail2ban/fail2ban/raw/1024452fe1befeb5a0a014386a81ec183cd45bb5/fail2ban/server/asyncserver.py
chmod 0644 /usr/lib/python3/dist-packages/fail2ban/{compat/async{hat,ore}.py,server/asyncserver.py}

The fail2ban package does not have 'python3-setuptools' listed under "Depends" in its control file, although it requires distutils (provided by the setuptools package) for its default sshd jail and thus for fail2ban to be able to run at all. So, unless you have already installed it, you will need to install it now:

apt install python3-setuptools

Once done, fail2ban should start successfully.