Comment 25 for bug 1786910

There is unattended-upgrade running background and every its in `/etc/apt/apt.conf.d/50unattended-upgrades`

It does upgrade if
Unattended-Upgrade::Allowed-Origins {
        "${distro_id}:${distro_codename}";
        "${distro_id}:${distro_codename}-security";

is available

you can comment
${distro_id}:${distro_codename}-security"; # (do it manually before release to prevent incident like this)

if you check /var/log/unattended-upgrades/unattended-upgrades.log
you can find monit is upgraded.