New CernVM images are released with the updated bootloader version 2021.03.
The bootloader contains an updated kernel and disables the RDS network protocol. Disabling RDS closes port 16385, which is inadvertently open on previous bootloader versions.
In order to update existing CernVMs, please run
sudo cernvm-update -k
and reboot. We recommend to take a VM snapshot with your hypervisor before updating.