Qubes-Community-Content/docs/privacy/anonymizing-your-mac-address.md

Anonymizing your MAC Address

Although it is not the only metadata broadcast by network hardware, changing the default MAC Address of your hardware could be an important step in protecting privacy.

Qubes OS 4.1 and higher already anonymize all Wifi MAC addresses by default - they change during every Wifi session. So there is no need to apply any of the below instructions if you're only interested in Wifi connections. Users requiring Ethernet MAC address anonymization may want to read on.

Randomize a single connection

Right click on the Network Manager icon of your NetVM in the tray and click 'Edit Connections..'.

Select the connection to randomize and click Edit.

Select the Cloned MAC Address drop down and set to Random or Stable. Stable will generate a random address that persists until reboot, while Random will generate an address each time a link goes up.

Save the change and reconnect the connection (click on Network Manager tray icon and click disconnect under the connection, it should automatically reconnect).

Randomize all Ethernet and Wifi connections

These steps should be done inside a template to be used to create a NetVM as it relies on creating a config file that would otherwise be deleted after a reboot due to the nature of AppVMs.

Write the settings to a new file in the /etc/NetworkManager/conf.d/ directory, such as 00-macrandomize.conf. The following example enables Wifi and Ethernet MAC address randomization while scanning (not connected), and uses a randomly generated but persistent MAC address for each individual Wifi and Ethernet connection profile.

[device]
wifi.scan-rand-mac-address=yes

[connection]
wifi.cloned-mac-address=stable
ethernet.cloned-mac-address=stable
connection.stable-id=${CONNECTION}/${BOOT}
#use random IPv6 addresses per session / don't leak MAC via IPv6 (cf. RFC 4941):
ipv6.ip6-privacy=2

• stable in combination with ${CONNECTION}/${BOOT} generates a random address that persists until reboot.
• random generates a random address each time a link goes up.

To see all the available configuration options, refer to the man page: man nm-settings

Next, create a new NetVM using the edited template and assign network devices to it.

Finally, shutdown all VMs and change the settings of sys-firewall, etc. to use the new NetVM.

You can check the MAC address currently in use by looking at the status pages of your router device(s), or inside the NetVM with the command sudo ip link show.

Anonymize your hostname

DHCP requests may also leak your hostname to your LAN. Since your hostname is usually sys-net, other network users can easily spot that you're using Qubes OS.

Unfortunately NetworkManager currently doesn't provide an option to disable that leak globally (Gnome Bug 768076). However the below alternatives exist.

Prevent hostname sending

NetworkManager can be configured to use dhclient for DHCP requests. dhclient has options to prevent the hostname from being sent. To do that, add a file to your sys-net template (usually the Fedora or Debian base template) named e.g. /etc/NetworkManager/conf.d/dhclient.conf with the following content:

[main]
dhcp=dhclient

Afterwards edit /etc/dhcp/dhclient.conf and remove or comment out the line starting with send host-name. If the file does not exist, you may be fine already. In any case it makes sense to double check your results on e.g. your home router, wireshark or tcpdump.

If you want to decide per connection, NetworkManager also provides an option to not send the hostname:
Edit the saved connection files at /rw/config/NM-system-connections/*.nmconnection and add the dhcp-send-hostname=false line to both the [ipv4] and the [ipv6] section.

Randomize the hostname

Alternatively you may use the following code to assign a random hostname to a VM during each of its startup. Please follow the instructions mentioned in the beginning to properly install it.

#!/bin/bash
set -e -o pipefail
#
# Set a random hostname for a VM session.
#
# Instructions:
# 1. This file must be placed and made executable (owner: root) inside the template VM of your network VM such that it will be run before your hostname is sent over a network.
# In a Fedora template, use `/etc/NetworkManager/dispatcher.d/pre-up.d/00_hostname`.
# In a Debian template, use `/etc/network/if-pre-up.d/00_hostname`.
# 2. Execute `sudo touch /etc/hosts.lock` inside the template VM of your network VM.
# 3. Execute inside your network VM:
#  `sudo bash -c 'mkdir -p /rw/config/protected-files.d/ && echo -e "/etc/hosts\n/etc/hostname" > /rw/config/protected-files.d/protect_hostname.txt'`


#NOTE: mv is atomic on most systems
if [ -f "/rw/config/protected-files.d/protect_hostname.txt" ] && rand="$RANDOM" && mv "/etc/hosts.lock" "/etc/hosts.lock.$rand" ; then
	name="PC-$rand"
	echo "$name" > /etc/hostname
	hostname "$name"
	#NOTE: NetworkManager may set it again after us based on DHCP or /etc/hostname, cf. `man NetworkManager.conf` @hostname-mode
	
	#from /usr/lib/qubes/init/qubes-early-vm-config.sh
	if [ -e /etc/debian_version ]; then
            ipv4_localhost_re="127\.0\.1\.1"
        else
            ipv4_localhost_re="127\.0\.0\.1"
        fi
        sed -i "s/^\($ipv4_localhost_re\(\s.*\)*\s\).*$/\1${name}/" /etc/hosts
        sed -i "s/^\(::1\(\s.*\)*\s\).*$/\1${name}/" /etc/hosts
fi
exit 0

Assuming that you're using sys-net as your network VM, your sys-net hostname should now be PC-[number] with a different [number] each time your sys-net is started.

Please note that the above script should not be added to /rw/config/rc.local) as that is executed only after the network fully started.