Is this a security backdoor? [duplicate]
Solution 1:
No it is not.
From https://wiki.ubuntu.com/Security/Privileges#Use_Network_Manager
All users at the console can manage Ethernet, wireless and 3G networks using Network Manager via DBus. (Ref.: /etc/dbus-1/system.d/NetworkManager.conf, /etc/dbus-1/system.d/nm-applet.conf)