[tor-bugs] #13667 [Tor]: Prevent port scanning of hidden services

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#13667: Prevent port scanning of hidden services
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     Reporter:  arma    |      Owner:
         Type:  defect  |     Status:  new
     Priority:  normal  |  Milestone:  Tor: 0.2.5.x-final
    Component:  Tor     |    Version:
   Resolution:          |   Keywords:  SponsorR tor-hs
Actual Points:          |  Parent ID:
       Points:          |
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Comment (by dgoulet):

 Started poking around a bit with this one. Here is what I think is
 possible.

 1) Send back "END_STREAM_REASON_CONNECTREFUSED" which does *not* fully
 tell if the port is open or not. It could be that the service *might*
 exists but misconfigured or not started.

 2) Drop the circuit with no reason which seems like a firewall with a DROP
 policy. However, I think it's pretty easy to link that to a "close port"
 for HS.

 3) Send back a mysterious reason with "END_STREAM_REASON_MISC" but I think
 it is also too easy to associate that reason with a closed port for HS.

 Usually firewall have two policies either DROP or REJECT (that sends a TCP
 reset) so at best I think we can make port scanning harder but not
 completely stop it. I would advocate for 1) here since it's actually a
 true and valid reason if the port is not supported by the HS and the other
 side (client) can't really confirm if it's a problem of the remote service
 or HS port.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13667#comment:2>
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