Since Debian stretch was released 2017-06-17 it was updated six times to 9.6 on 2018-11-10.

Update 2019-01-28

Over the weekend the debian team released the update to the normal stable-updates channel.

To resume to the normal update path run these commands:

sudo apt update && sudo apt upgrade && sudo apt autoremove
sudo apt dist-upgrade

To cleanup the backports run:

sudo rm /etc/apt/sources.list.d/stretch-backports.list

Backports

For certbot this means that its version was frozen two years ago. Since then there have been problems with the TLS-SNI-01 method so it will be removed in February 2019.

A newer version of certbot is available in debian backports and here is how to enable it.

Applied how to based on general instructions

First we will add support for tls to apt:

sudo apt install apt-transport-https

Then we will add the backports repo to the system:

echo "deb https://debian.ethz.ch/debian stretch-backports main contrib" | sudo tee /etc/apt/sources.list.d/stretch-backports.list

After that we have to fetch the list of available packages:

sudo apt update

Finally we can update from the main package to the backports package:

sudo apt install -t stretch-backports certbot