Created attachment 222321 [details]
dmesg

Created attachment 222322 [details]
daemon.log

- In a live environment (32-bits), I cannot add a wireless connection. This results in a "Insufficient privileges" message.
- Live user has root permissions.
- Distribution based on Debian Testing.
- No wpa_supplicant logs are created.
- I cannot confirm this happening on a 64-bit system.
- Once installed I have no problem making new wireless connections.

As Debian uses ifupdown, has it been tested that this is actually an issue in upstream code?

Can you explain how I could do so?
In other words: what information do you need?
(In reply to comment #4)
> As Debian uses ifupdown, has it been tested that this is actually an issue in
> upstream code?

# ip link
3: waln0: <NO-CARRIER,BROADCAST,MULTICAST,UP> ...

# ip route
Returns nothing

# ifdown wlan0
ifdown: interface wlan0 not configured

# modprobe -r brcmsmac ; modprobe brcmsmac
Returns nothing

# ifup wlan0
Ignoring unknown interface wlan0=wlan0

Obviously, trying to configure wireless through network-manager results in the above mentioned error message.

The "Insufficient privileges" error for adding connections means that PolicyKit
permissions forbid the action.
The configuration file is something like
/usr/share/polkit-1/actions/org.freedesktop.NetworkManager.policy

You can query the permissions like this:
dbus-send --system --print-reply --dest=org.freedesktop.NetworkManager /org/freedesktop/NetworkManager org.freedesktop.NetworkManager.GetPermissions

or

nmcli nm perm

The whole thing looks like Debian-specific and thus you are better off going to a Debian bug tracker.

You are probably right that this is a Debian issue, but can you be exactly sure?

Here's the output. You can see that all are set to "no" (contrary to the none-live-environment). What could be the cause of this?

$ dbus-send --system --print-reply --dest=org.freedesktop.NetworkManager /org/freedesktop/NetworkManager org.freedesktop.NetworkManager.GetPermissions            
method return sender=:1.0 -> dest=:1.84 reply_serial=2                                                                                                                          
   array [                                                                                                                                                                      
      dict entry(                                                                                                                                                               
         string "org.freedesktop.NetworkManager.network-control"                                                                                                                
         string "no"                                                                                                                                                            
      )                                                                                                                                                                         
      dict entry(
         string "org.freedesktop.NetworkManager.enable-disable-wwan"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.settings.modify.own"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.wifi.share.protected"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.wifi.share.open"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.enable-disable-network"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.enable-disable-wimax"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.sleep-wake"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.enable-disable-wifi"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.settings.modify.system"
         string "no"
      )
      dict entry(
         string "org.freedesktop.NetworkManager.settings.modify.hostname"
         string "no"
      )
   ]

For the past week I've been upgrading the 32-bit version in groups of packages. This way I narrowed this issue down to one single package: xinit

xinit upgraded from 1.3.1-1 to 1.3.2-1.
So I held back that package, did a dist-upgrade and booted the iso with the following results:
1. The shut down and restart buttons are back in the Kickoff menu.
2. I can make a wireless connection.
3. I can mount USB

Hmm, it seems odd to me that xinit would do something with the polkit stuff.
But anyway, it's good that you've solved your issue.