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This question already has an answer here:

Assuming someone knows my MAC ddress (someone inside my network or outside), could they exploit it or do some action on my behalf or any action that needs to be considered?

Because I have noticed some people on YouTube hide their MAC address.

marked as duplicate by techraf, Gilles, Anders, Xander, André Borie Jul 19 '16 at 23:39

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Your MAC address is your machine's hardware address. This is mostly only important when an attacker is on the same network as you. At this point an attacker could do deauth attacks or intercept your traffic by posing as the networks router. However if an attacker is on or near your network is is trivial to get your MAC address. You can also change your MAC address as you please. The people trying to hide their MAC address likely do not fully understand networking and erroneously believe it to be a risk.

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MAC addresses aren't particularly sensitive, and are only available in your local network. The MAC address isn't available once the traffic leaves your local area network, although if you're using IPV6 your IP address may be based on the MAC address.

However, sometimes the MAC address is used, and embedded in the meta-data of some versions of Office products. An attacker might be able to identify you as the author of a document if he/she were to know your MAC address. This was true a number of years ago with Microsoft Office. I'm not sure if it's still the case, or if any other files contain the MAC address as meta-data of the file creator.

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Someone on the same broadcast domain could direct traffic to their machine by announcing their IP address mapped to your MAC address and then forward on the traffic acting as MITM.

Of course, if all your traffic is encrypted, this is somewhat limited, but they still will see meta data e.g. the servers you are communicating with but not the content.

  • this is an unlikely scenario unless the MAC in question is a destination (more typically, the gateway or a server) – schroeder Jul 19 '16 at 21:20
  • @schroeder - its possible, and thats what the spirit of the question was. – Darragh Jul 21 '16 at 21:54
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Already in the 1980s it was possible in the WDC-adapter drivers to replace the hardware MAC address with another address. So if I knew your MAC address and I saw that you left the subnet, I could pretend to be you (your computer), run a torrent server, send spam mails, threat mails, start hacking attempts, you name it. And on the next morning, it's not the milkman who's knocking on your door.

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    how does the MAC survive an email? – schroeder Jul 19 '16 at 21:18
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    @schroeder The MAC-address is not in an e-mail. The IP-address is in it. And there is a mapping, the DHCP-server will log it. – ott-- Jul 19 '16 at 21:22
  • Except that it is easy to spoof the MAC, and investigators know that. I'm not sure that I'm following your logic here. At best, you hide your tracks, not place suspicion on the innocent party. – schroeder Jul 19 '16 at 21:38
  • @schroeder So the investigators get the DHCP-server log, see the mapping IP to MAC address and they will say "Everyone can forge the MAC-address. We'll never find out who that really was. Case closed.". – ott-- Jul 19 '16 at 21:56