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Privacy concerns with DHCP (DHCP fingerprinting) (lemmy.zip)
submitted 2 years ago* (last edited 2 years ago) by to c/privacy@lemmy.ml
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So many people here will go though great lengths to protect themselves from fingerprinting and snooping. However, one thing tends to get overlooked is DHCP and other layer 3 holes. When your device requests an IP it sends over a significant amount of data. DHCP fingerprinting is very similar to browser fingerprinting but unlike the browser there does not seem to be a lot of resources to defend against it. You would need to make changes to the underlying OS components to spoof it.

What are everyone's thoughts on this? Did we miss the obvious?

https://www.arubanetworks.com/vrd/AOSDHCPFPAppNote/wwhelp/wwhimpl/common/html/wwhelp.htm#href=Chap2.html&single=true

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[–] 12 points 2 years ago (2 children)

I feel like I'm missing something here...

Who's going to be fingerprinting DHCP messages on your home network?

Outside of that, fingerprinting or tracking any DHCP info would be the least of my concerns. You have 0 control over any data the moment your devices connect to a public network. What use is DHCP info when you can person-in-the middle all the traffic anyway?

And anyway, what info are you concerned about? Having had a VERY quick browse of RFC2131 the worst thing would be "leaking" the device MAC address which can be discovered via several other means anyway

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  • [–] 5 points 2 years ago (3 children)

    I guess the hostname could be used to defeat MAC randomization if you use public WiFi like hotels, airports and coffee shops. You could probably identify repeat users if you cared enough.

    But then your worry should be the security cameras not the WiFi, because that's what's gonna tie you personally to your device connecting.

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  • [–] 3 points 2 years ago* (2 children)

    Your router always knows your Mac address, no matter how you got your ip assigned. And yes, you can use it to identify the client - that is why it is there. This whole post is nonsense written by someone who doesn't really understand what dhcp is or how it works. Long story short, don't look for privacy on local Ethernet segment :D

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  • [–] 2 points 2 years ago (2 children)

    Most modern operating systems randomize the MAC. DHCP does have extra fields such as the device's hostname that can be used to counter that.

    But as I said, that's unlikely to be the weakest link. If you don't trust the network you're also likely in a public environment where people can just see you anyway.

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  • [–] 4 points 2 years ago (2 children)

    Most modern operating systems randomize the MAC.

    [citation needed]
    having the option to randomize the MAC is not the same as actually doing that. There are also a few downsides to random MACs, like captive portals not remembering you on public WiFis.

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  • [–] 1 point 2 years ago (2 children)

    Most modern operating systems randomize the MAC.

    that doesn't seem to be uniform behaviour. but i think we agree on the merit. if you are this paranoid, you just don't use networks where you don't have control over the local segment.

    [admin@MikroTik] > ip arp print 
Flags: X - disabled, I - invalid, H - DHCP, D - dynamic, P - published, C - complete 
 #    ADDRESS         MAC-ADDRESS       INTERFACE                                                    
 0 DC 192.168.88.160  A2:35:xx:xx:xx:xx bridge                                                       
 1 DC 192.168.88.159  F4:60:xx:xx:xx:xx bridge                                                       
 2 DC 192.168.0.1     44:32:xx:xx:xx:xx ether1                                                       
 3 DC 192.168.88.168  18:3D:xx:xx:xx:xx bridge                                                       
 4 DC 192.168.88.156  70:BB:xx:xx:xx:xx bridge

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  • [–] 1 point 2 years ago (1 child)

    you just don't use networks where you don't have control over the local segment.

    Easier said than done. Sometimes it's not an option.

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  • [–] 1 point 2 years ago

    there is always an option. unless you are pressured by lets say some state authority or your employee, in which case your identity is probably well known and they don't really need to spy on you through dhcp.

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  • [–] 1 point 2 years ago (1 child)

    Long story short, don't look for privacy on local Ethernet segment :D

    You seem to be forgetting that a lot of people use portable devices on other networks than their home one.

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  • [–] 1 point 2 years ago

    i am not forgetting anything. using your portable device on network other than your own is your free choice and if you are such control freak that you are afraid of being spied on through dhcp, you probably should not do that.

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  • [–] [S] -1 points 2 years ago (1 child)

    See the linked page

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  • [–] 2 points 2 years ago

    You need to say more than that about what your concern is, especially on devices configured for Mac randomization and other privacy features.

    Aruba is looking at the dhcp traffic and inferring information about the device. The device is not sending all of this data.

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