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[Martin Pitt <martin.pitt@xxxxxxxxxx>]

** Changed in: systemd (Ubuntu)
       Status: New => Triaged

** Changed in: systemd (Ubuntu)
   Importance: Undecided => Low

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https://bugs.launchpad.net/bugs/1449001

Title:
  systemd-resolved: please do not use Google public DNS by default

Status in systemd:
  Unknown
Status in systemd package in Ubuntu:
  Triaged

Bug description:
  systemd-resolved will fall back to Google public DNS (8.8.8.8, etc.)
  in the absence of other configured DNS servers.

  systemd-resolved is not enabled by default in Ubuntu 15.04, but it is
  installed by default and will behave in this way if enabled by the
  user.

  $ cat /etc/systemd/resolved.conf 
  (...)
  # Entries in this file show the compile time defaults.
  (...)
  #FallbackDNS=8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844

  This raises privacy concerns since in the event of accidental
  misconfiguration DNS queries will be sent unencrypted across the
  internet, and potentially also security concerns given systemd-
  resolved does not perform DNSSEC validation and is not particularly
  well hardened against malicious responses e.g. from a MITM
  (http://www.openwall.com/lists/oss-security/2014/11/12/5).

  I believe that it would be better to fail safe if no DNS server is
  configured -- i.e. have DNS lookups fail; it's better that the user is
  aware of their misconfiguration, rather than silently sending their
  queries to Google.  The user can intentionally opt to use Google
  public DNS if they wish.


  Steps to reproduce:
  1. Remove existing DNS configuration (from /etc/network/interfaces, /etc/resolv.conf, /etc/resolvconf/resolv.conf.d/*)
  2. Reboot, or otherwise clear relevant state
  3. sudo service systemd-resolved start
  4. Note that Google's servers are listed in /run/systemd/resolve/resolv.conf
  5. If systemd-resolved is enabled in /etc/nsswitch.conf (it isn't by default), observe that DNS lookups probably still work, and queries are being sent to one of Google's servers

  
  Possible workaround/bugfix: ship a resolved.conf which clears the FallbackDNS parameter.

  
  This issue has been discussed in the Debian BTS (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=761658).  My interpretation of the Debian package maintainer's position is that a user concerned with the privacy implications shouldn't let systemd get into a state where it uses the fallback DNS servers (quoting Marco d'Itri: "Short summary: have a resolv.conf file or use DHCP").  I would argue that it's safest not to have fallback DNS servers configured at all by default.

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