[Bug 1883793] Re: systemd-resolved leaks mDNS queries to DNS

[Steve Beattie]

** Information type changed from Private Security to Public Security

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Title:
  systemd-resolved leaks mDNS queries to DNS

Status in systemd package in Ubuntu:
  New

Bug description:
  On a freshly installed ubuntu focal machine, access to local machines
  advertised via mDNS is now broken. This is a regression wrt eoan where
  it used to work.

  Trying to ping something like <host>.local invariably results in
  pinging 40.68.249.35 because systemd-resolved passes the query to the
  DNS even if .local is reserved for multicast DNS and for some reasons
  <anything>.local seems to resolve to 40.68.249.35.  This happens even
  if the avahi daemon is up and running.

  Stopping systemd-resolved makes the mDNS resolution work as expected.

  Not only this breaks standard workflows, but it also means that anyone
  pretending to be 40.68.249.35 on the network could probably
  impersonate any local host.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: systemd 245.4-4ubuntu3.1
  ProcVersionSignature: Ubuntu 5.4.0-37.41-generic 5.4.41
  Uname: Linux 5.4.0-37-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.2
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: KDE
  Date: Tue Jun 16 23:43:22 2020
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2020-02-16 (121 days ago)
  InstallationMedia: Kubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
  MachineType: SCHENKER SCHENKER_SLIM14_SSL14L19
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-37-generic root=/dev/mapper/VG_NVMe-root ro quiet splash vt.handoff=7
  SourcePackage: systemd
  SystemdDelta:
   [EXTENDED]   /usr/lib/systemd/system/rc-local.service → /usr/lib/systemd/system/rc-local.service.d/debian.conf
   [EXTENDED]   /usr/lib/systemd/system/user at .service → /usr/lib/systemd/system/user at .service.d/timeout.conf
   
   2 overridden configuration files found.
  UpgradeStatus: Upgraded to focal on 2020-05-23 (24 days ago)
  dmi.bios.date: 10/02/2019
  dmi.bios.vendor: INSYDE Corp.
  dmi.bios.version: 1.07.04RTR1
  dmi.board.asset.tag: Tag 12345
  dmi.board.name: N141CU
  dmi.board.vendor: SCHENKER
  dmi.board.version: Not Applicable
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 10
  dmi.chassis.vendor: Notebook
  dmi.chassis.version: N/A
  dmi.modalias: dmi:bvnINSYDECorp.:bvr1.07.04RTR1:bd10/02/2019:svnSCHENKER:pnSCHENKER_SLIM14_SSL14L19:pvrNotApplicable:rvnSCHENKER:rnN141CU:rvrNotApplicable:cvnNotebook:ct10:cvrN/A:
  dmi.product.family: Not Applicable
  dmi.product.name: SCHENKER_SLIM14_SSL14L19
  dmi.product.sku: Not Applicable
  dmi.product.version: Not Applicable
  dmi.sys.vendor: SCHENKER

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