From Ludwid Nussel:

nm-applet.conf contains the following rules:

<policy context="default"> <allow senddestination="org.freedesktop.NetworkManagerUserSettings"/> <allow sendinterface="org.freedesktop.NetworkManagerSettings"/> <!-- Only root can get secrets --> <deny sendinterface="org.freedesktop.NetworkManagerSettings.Secrets"/>

Ie anyone can call methods on destination org.freedesktop.NetworkManagerUserSettings. There is a line that is supposed to block users from calling the GetSecrets method on the separate interface for secrets. Unfortunately that interface is not called "org.freedesktop.NetworkManagerSettings.Secrets" but "org.freedesktop.NetworkManagerSettings.Connection.Secrets". So the deny statement is useless and any user on the system can fetch the connection secrets. The same problem can be found in nm-system-settings.

Acknowledgements:

Red Hat would like to thank Ludwig Nussel for reporting this flaw responsibly.