[tor-bugs] #17782 [Tor]: Relays may publish descriptors with incorrect IP address

[Tor Bug Tracker & Wiki]

#17782: Relays may publish descriptors with incorrect IP address
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 Reporter:  fk      |          Owner:
     Type:  defect  |         Status:  new
 Priority:  High    |      Milestone:  Tor: 0.2.7.x-final
Component:  Tor     |        Version:  Tor: 0.2.7.4-rc
 Severity:  Major   |     Resolution:
 Keywords:          |  Actual Points:
Parent ID:          |         Points:
  Sponsor:          |
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Comment (by teor):

 Tor currently uses the following sources to determine its IP address:
 * Address configuration in the torrc
 * Hostname lookup
   * This can sometimes be unreliable, see #17765
 * Interface addresses (if publicly routable)
   * This could be unstable in the presence of multiple interface addresses
 (#17787)
 * X-Your-IP-Address-Is header from directory servers
   * This was recently an issue with the authority Faravahar, where the
 provider was providing a "transparent" web proxy on it's DirPort that was
 repeating these headers, forwarding some requests so that they appeared to
 originate from the authority's old IP address, and corrupting some
 responses. (See #16205 / #17605)

 Therefore, this issue only affects relays:
 * without Address configured in their torrc
 * with a hostname that doesn't resolve, or that resolves to a private
 address
 * with no publicly routable addresses on any interfaces (that is, behind
 NAT)

 A quick mitigation for this issue would be to encourage every relay
 operator on a stable external IPv4 address, or stable hostname that always
 resolves to the correct IPv4 address, to add an Address line to their
 torrc.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17782#comment:2>
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