## 7 Discussion of the Filtering Impact on Security and Privacy
### Influence of Filtering on STRIDE Attack Vectors
The exception is the case of a DoS attack that targets not one of the local devices but a remote server, in which case the impact is rated as _no or low_ (_DOS_). _INE, RNE:_  
The insertion of traffic directed to a destination outside the local network, such as a control server, cannot be prevented by the home router. The opposite direction is also unlikely to have a great impact, assuming an attacker spoofs a whitelisted address. The effect is then limited to reducing the number of endpoints that can be spoofed for a device. Overall, therefore, a rating of _no or low_ impact is assigned for both directions (_INE, RNE_). _INL, RNL:_  
As _Bark_ does not appear to enforce a correct mapping between MAC and IP addresses, a host can in principle send packets with spoofed IP addresses. However, similar to DoS attacks, the _Bark_ filtering approach can prevent the insertion of traffic, benign or malicious, if it is not whitelisted. It is also assumed that MAC spoofing is not possible for a device connected over WLAN if different pre-shared keys are used for each device. This is because the device cannot send packets with a different MAC address unless it also knows the corresponding key. However, as discussed above, there is a possibility that wired clients, which were not considered in the approach, could defeat the filtering mechanisms by spoofing their MAC addresses. Assuming that most devices are connected wirelessly (this is likely due to the fact that Smart Home Devices are intended to be placed all over the house and is also indicated by looking at the devices tested by other researchers, such as those listed in ([17], Table II)), a _medium_ influence rating is assigned here (_INL, RNL_). _MAC, MAH, URC, USC:_  
While in principle there is no direct influence on the vulnerability of missing access control or authorisation checks, _Bark_ can still prevent the attack if the relevant communication is not whitelisted, as discussed in the previous paragraph. The same applies to the input of credentials, whether stolen or guessed. It is assumed that there is no need to access a service (such as SSH or Telnet) if the device is not allowed to log in or perform actions that are not checked. Therefore, a _high_ influence rating is assigned (_MAC, MAH, URC, USC_). _MAS:_  
Obviously, a filtering approach deployed in the home network has _no or only low_ influence on missing authorisation checks on the server (_MAS_). _MME:_  
For the first sub-vector, DNS spoofing, no influence is assumed because in this case the router itself would be the target of the attack and there is no restriction on its own communication that is considered in the filtering approach. Similarly, no influence is assumed in the case of an attacker with physical access to a router or a link on the route. In the case of an Evil Twin, the fact that the clients all use different pre-shared keys makes it impossible for someone who only knows their own password to set up a protected access point that can communicate with any of the other devices. However, it is still possible to simply provide an open access point, even if some devices refuse to connect to it. Therefore, only some influence can be considered for this sub-vector. Note, if a strong end-to-end encryption is additionallyused, including the authentication of the end point to prevent a man-in-the-middle attack on the encrypted end-to-end channel (e.g., https connections with added mechanisms like certificate pinning [92]), then facilitating such an encrypted communication channel can help to protect against MME and MML (see below). Overall, the influence of filtering is rated as _no or only low_ for this man-in-the-middle attack (_MME_). _MML:_  
The influence on MAC address spoofing has already been discussed. For ARP spoofing [95], this means that wired clients can spoof all other clients, while their wireless counterparts can only spoof the devices to which they have access.