A critical vulnerability in the Debian (and Debian derivatives like Ubuntu) update tool Apt has been discovered. It's possible to execute a man-in-the-middle attack on updates. If your systems are affected you should update them as soon as possible.
https://justi.cz/security/2019/01/22/apt-rce.html
https://www.theregister.co.uk/2019/01/22/debian_package_manager_flaws/
https://justi.cz/security/2019/01/22/apt-rce.html
https://www.theregister.co.uk/2019/01/22/debian_package_manager_flaws/