Joe via Tails-dev (2025-06-15):
> Dear Tails Development Team,
>
> I hope this message finds you well. I am writing to bring to your attention
> an important consideration regarding the MAC spoofing feature in Tails. The
> existing MAC spoofing feature in Tails OS is a step in the right direction,
> as it checks for NIC existence and retries if necessary, treating the NIC as
> a unique identifier for WiFi cards. While the current implementation
> effectively changes the NIC part of the MAC address, it leaves the OUI
> (Organizationally Unique Identifier) exposed, which can potentially
> compromise user anonymity.
>
> The OUI part of the MAC address identifies the device manufacturer, and if
> left unchanged, it can be used for device fingerprinting. This is
> particularly concerning for users such as journalists and whistleblowers who
> rely on Tails for privacy. The current setup inadvertently makes these users
> unique, as the OUI remains constant, even when the NIC is spoofed.
>
> As noted in the Tails documentation on MAC address limitations, tools like
> Macchiato may rely on outdated OUI lists, potentially increasing uniqueness.
> Ironically, the current Tails implementation already risks this by
> maintaining a consistent OUI, making it trivial for entities like ISPs to
> track devices across sessions. If you are using tails at home your ISP or
> anyone monitoring your network that its the same device on the network since
> the OUI is always the same.
>
> This especially true for users on dedicated devices such as journalists or
> whistleblowers. I'm sure many journalists, whistleblowers, or privacy folks
> may strictly have a separate computer or throwaway dedicated device that they
> only use with Tails. Well, those devices most likely have a common or unique
> OUI especially if they are older devices. Many such users might also attempt
> mitigations, like purchasing external ethernet or WiFi adapters, but this
> often deanons them through traceable purchases since most are going to
> purchase these through sites like Amazon which require credit cards.
>
> Mind you the best case of action would to be spoofing both OUI and NIC in the
> mac address design. Most notably android and Iphone already support this and
> do this though their design is flawed since it is only per network and not
> per connection to a network. Up until recently it was discovered that iOS
> prior to version 17.1, leaked real MAC on port 5353.
>
> * Proposed Solution *
>
> To enhance anonymity, I propose spoofing both the OUI and NIC parts of the
> MAC address. While systems like Android and iOS have similar implementations,
> they are limited to per-network changes. However, the approach can be adapted
> and improved for Tails.
>
> * DHCP Considerations *
>
> When implementing full MAC spoofing, it's crucial to handle DHCP leasing
> correctly. If a spoofed MAC is already leased, the device may fail to obtain
> an IP address or fail to connect to the internet. To mitigate this, I suggest
> integrating an ARP check using `arping` to ensure the new MAC is not already
> in use before connecting.
>
> If the DHCP server detects that the MAC address is already associated with an
> active lease, it may refuse to assign a new IP address to your system. Send a
> DHCP NAK (negative acknowledgment) to your system, indicating that it cannot
> assign an IP address. If does the allow you to connect with an already leased
> MAC you most likely will not be able to connect to the internet. In
> environments with MAC spoofing detection, such as those using Dynamic ARP
> Inspection (DAI), the spoofed ARP requests could be ignored or flagged,
> potentially leading to no responses. However, these advanced security
> features are less common on public WiFi networks with captive portals, where
> basic DHCP setups predominate, reducing the likelihood of such detections.
>
> To my knowledge NetworkManager or Linux in general will not explicitly retry
> with a new spoofed mac if there is already is a device leased with the same
> MAC address already on a network.
> Currently it looks like `iputils-arping` is not installed on tails but could
> possibly be incorporated into the existing design?
>
> * Example Code Implementation *
>
> The following is example code modifications that could can be incorporated to
> include the ARP check:
>
> **Modify `spoof_mac` Function:**
>
> ```bash
> spoof_mac() {
> local max_retries=3
> local attempt=1
> local msg
> local new_mac
> local gateway_ip
>
> gateway_ip=$(ip route show | grep default | awk '{print $3}')
>
> set +e
> while [ "${attempt}" -le "${max_retries}" ]; do
> msg="$(macchanger -e "${1}" 2>&1)"
> ret="${?}"
> set -e
>
> if [ "${ret}" != 0 ]; then
> log "macchanger failed for NIC ${1}, returned ${ret} and said:
> ${msg}"
> unset NEW_MAC
> break
> fi
>
> NEW_MAC="$(get_current_mac_of_nic "${1}")"
> if [ "${OLD_MAC}" != "${NEW_MAC}" ]; then
> log "Spoofed MAC for NIC ${1} is: ${NEW_MAC}"
> log "Checking if MAC ${NEW_MAC} is already leased..."
>
> if arping -c 1 -I "${1}" -s "${NEW_MAC}" "${gateway_ip}" &>
> /dev/null; then
> log "MAC ${NEW_MAC} is already leased or in use on NIC ${1}."
> attempt=$((attempt + 1))
> continue
> else
> log "No conflict detected for MAC ${NEW_MAC}."
> return 0
> fi
> fi
> attempt=$((attempt + 1))
> done
> set +e
> return 1
> }
> ```
>
> **Add Error Handling and Logging:**
>
> ```bash
> for i in 1 2 3; do
> if ! spoof_mac "${NIC}"; then
> unset NEW_MAC
> break
> fi
> NEW_MAC="$(get_current_mac_of_nic "${NIC}")"
> if [ "${OLD_MAC}" != "${NEW_MAC}" ]; then
> log "Checking if MAC ${NEW_MAC} is already leased..."
> if arping -c 1 -I "${NIC}" -s "${NEW_MAC}" "${gateway_ip}" &>
> /dev/null; then
> log "MAC ${NEW_MAC} is already leased, retrying spoofing..."
> continue
> fi
> break
> fi
> done
> ```
>
>
> Enhancing MAC spoofing to include both OUI and NIC, along with ARP checks,
> would significantly improve user anonymity in Tails and avoid failure if a
> leased device on a network already has the same MAC as the Spoofed one. If
> there is not way to anonymously check DHCP leases with leaking the real MAC
> address through ARP ping/requests then forget this but rather focus on new
> mac spoofing design that spoofs full mac address.
>
> Thank you for your dedication to Tails and user privacy.
>
> Namaste,
>
> Joe
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--
intrigeri
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