Comment 13 for bug 1581535

To manually upgrade network-manager, visit this launchpad page: https://launchpad.net/ubuntu/trusty/amd64/network-manager/0.9.8.8-0ubuntu7.3

The link with the 7.3 version .deb is on the right-hand side, transfer to the affected computer via USB key or other means, and double-click on the .deb file. This will let you upgrade. After that, reboot (doing only service restart did not work), and use Synaptic to upgrade libnm-util2, libnm-glib4, libnm-glib-vpn1, and gir1.2-networkmanager-1.0