30 Sep
2021
30 Sep
'21
10 p.m.
The cause is a security update to apache2, which was released on the 28th. It's got regression problems. There's been another update today, which doesn't fix it. I've reported the bug to Ubuntu:
https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1945710
You can work around the issue by force downgrading your apache2 packages to previous versions, but then you won't have any of the apache2 security fixes on your system:
aptitude install apache2=2.4.41-4ubuntu3 libapache2-mod-proxy-uwsgi=2.4.41-4ubuntu3 apache2-bin=2.4.41-4ubuntu3 apache2-utils=2.4.41-4ubuntu3 apache2-data=2.4.41-4ubuntu3
Doing that brought mailman3 back to life again, but I'm not very comfortable running an insecure apache2 package
Tim