[tor-bugs] #31009 [Core Tor/Tor]: Tor lets transports advertise private IP addresses in descriptor

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#31009: Tor lets transports advertise private IP addresses in descriptor
------------------------------+--------------------
     Reporter:  phw           |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:  0.5           |   Reviewer:
      Sponsor:                |
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 While dealing with broken obfs4 bridges, I realised that our bridge
 authority has several obfs4 bridges in its cached-extrainfo document that
 have private IP addresses, e.g.:
 {{{
 transport obfs4 10.0.254.17:[redacted]
 }}}

 The PT spec [https://gitweb.torproject.org/torspec.git/tree/pt-
 spec.txt?id=4707f3604cd06e3a627980c6863cca556f9f21a4#n305 explicitly
 allows private addresses] in `TOR_PT_SERVER_BINDADDR`:
 > The <address> MAY be a locally scoped address as long as port forwarding
 is done externally.
 [[br]]
 BridgeDB however ignores bridges with private IP addresses, so these obfs4
 bridges are effectively useless. We could address this issue in BridgeDB
 by replacing an obfs4 bridge's private IP address with the address in its
 ORPort but I think that tor shouldn't be writing private addresses to a
 descriptor in the first place.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31009>
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