XDMCP server starts without authentication if configured key does not exist

Bug #1517685 reported by Robert Ancell on 2015-11-19
262
This bug affects 2 people
Affects Status Importance Assigned to Milestone
Light Display Manager
Medium
Robert Ancell
1.10
Medium
Robert Ancell
1.14
Medium
Robert Ancell
1.16
Medium
Robert Ancell
1.2
Medium
Robert Ancell
lightdm (Ubuntu)
Medium
Robert Ancell
Precise
Medium
Unassigned
Trusty
Medium
Robert Ancell
Vivid
Medium
Robert Ancell
Wily
Medium
Robert Ancell

Bug Description

[Impact]
An incorrectly configured XDMCP server will start without authentication instead of disabling XDMCP / stopping LightDM.

[Test Case]
1. Set up LightDM to run an XDMCP server using an XDM authentication key, i.e. in lightdm.conf:
[XDMCPServer]
enabled=true
key=key-name
2. Do not create /etc/lightdm/keys.conf or do not define 'key-name' in keys.conf.
3. Start LightDM
4. Connect XDMCP client.

Expected result:
Either LightDM doesn't start or the XDMCP server doesn't start.

Observed result:
XDMCP server starts without authentication, any XDMCP client is able to connect. Debug message printed to log warning about missing key, but not easy to spot.

[Regression Potential]
Low - change is to not start LightDM if this case occurs. This could affect someone who currently has a misconfigured LightDM. In this case a warning message is printed to the log.

information type: Private Security → Public Security
Changed in lightdm:
milestone: none → 1.17.2
status: In Progress → Fix Released
affects: ubuntu (Ubuntu) → lightdm (Ubuntu)

Hello Robert, or anyone else affected,

Accepted lightdm into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/lightdm/1.10.6-0ubuntu1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in lightdm (Ubuntu Trusty):
status: New → Fix Committed
tags: added: verification-needed
Brian Murray (brian-murray) wrote :

Hello Robert, or anyone else affected,

Accepted lightdm into wily-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/lightdm/1.16.6-0ubuntu1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in lightdm (Ubuntu Wily):
status: New → Fix Committed
Brian Murray (brian-murray) wrote :

Hello Robert, or anyone else affected,

Accepted lightdm into vivid-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/lightdm/1.14.4-0ubuntu1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in lightdm (Ubuntu Vivid):
status: New → Fix Committed
tags: added: verification-needed-trusty verification-needed-vivid verification-needed-wily
removed: verification-needed
Robert Ancell (robert-ancell) wrote :

Confirmed on trusty that LightDM does not start when XDMCP is configured with an unknown key.

tags: added: verification-done-trusty
removed: verification-needed-trusty
Changed in lightdm (Ubuntu):
assignee: nobody → Robert Ancell (robert-ancell)
importance: Undecided → Medium
Changed in lightdm (Ubuntu Precise):
assignee: nobody → Robert Ancell (robert-ancell)
importance: Undecided → Medium
Changed in lightdm (Ubuntu):
status: New → Fix Released
Changed in lightdm (Ubuntu Trusty):
assignee: nobody → Robert Ancell (robert-ancell)
Changed in lightdm (Ubuntu Vivid):
assignee: nobody → Robert Ancell (robert-ancell)
importance: Undecided → Medium
Changed in lightdm (Ubuntu Wily):
assignee: nobody → Robert Ancell (robert-ancell)
importance: Undecided → Medium
Changed in lightdm (Ubuntu Trusty):
importance: Undecided → Medium
Robert Ancell (robert-ancell) wrote :

Confirmed on vivid that LightDM does not start when XDMCP is configured with an unknown key.

tags: added: verification-done-vivid
removed: verification-needed-vivid
Robert Ancell (robert-ancell) wrote :

Confirmed on wily that LightDM does not start when XDMCP is configured with an unknown key.

tags: added: verification-done-wily
removed: verification-needed-wily
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package lightdm - 1.10.6-0ubuntu1

---------------
lightdm (1.10.6-0ubuntu1) trusty; urgency=medium

  * New upstream release:
    - Handle trailing whitespace on boolean values in configuration.
      (LP: #1507033)
    - Use libaudit to generate audit events.
    - Fix apparmor profiles for running Chromium in guest sessions.
      (LP: #1504049)
    - Add LC_PAPER, LC_NAME, LC_ADDRESS, LC_TELEPHONE, LC_MEASUREMENT and
      LC_IDENTIFICATION variables to the list of inherited locale variables.
      (LP: #1511259)
    - Add a backup-logs option that can be used to disable existing logging
      files having a .old suffix added to them.
    - Check the version of the X server we are running so we correctly pass
      -listen tcp when required. (LP: #1449282)
    - Use IP address of XDMCP requests to contact X server if available.
      (LP: #1481561)
    - Implement XDMCP ForwardQuery. (LP: #1511545)
    - Add an option for XDMCP and VNC servers to only listen on one address.
      (LP: #1390808)
    - Don't start LightDM if the XDMCP server is configured with a key that
      doesn't exist. (LP: #1517685)
    - Add IP addresses to XDMCP log messages.
    - Refactor XDMCP error handling.
    - Fix small memory leak in XDMCP logging code.
    - Fix typo in dm-tool man page. (LP: #1470587)
    - Use new Xmir binary when running X under Unity System Compositor.
    - Fix all the things that prevent clang (3.5) from building LightDM with
      -Werror.
    - Add more tests.

 -- Robert Ancell <email address hidden> Fri, 20 Nov 2015 16:07:50 +1300

Changed in lightdm (Ubuntu Trusty):
status: Fix Committed → Fix Released

The verification of the Stable Release Update for lightdm has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

Launchpad Janitor (janitor) wrote :

Status changed to 'Confirmed' because the bug affects multiple users.

Changed in lightdm (Ubuntu Precise):
status: New → Confirmed
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package lightdm - 1.16.6-0ubuntu1

---------------
lightdm (1.16.6-0ubuntu1) wily; urgency=medium

  * New upstream release:
    - Handle XDMCP Request packet with no addresses. (LP: #1516831)
    - Don't start LightDM if the XDMCP server is configured with a key that
      doesn't exist. (LP: #1517685)
    - Add IP addresses to XDMCP log messages.
    - Refactor XDMCP error handling.
    - Add more tests.

 -- Robert Ancell <email address hidden> Fri, 20 Nov 2015 15:46:15 +1300

Changed in lightdm (Ubuntu Wily):
status: Fix Committed → Fix Released
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package lightdm - 1.14.4-0ubuntu1

---------------
lightdm (1.14.4-0ubuntu1) vivid; urgency=medium

  * New upstream release:
    - Handle XDMCP Request packet with no addresses. (LP: #1516831)
    - Don't start LightDM if the XDMCP server is configured with a key that
      doesn't exist. (LP: #1517685)
    - Add IP addresses to XDMCP log messages.
    - Refactor XDMCP error handling.
    - Add more tests.

 -- Robert Ancell <email address hidden> Fri, 20 Nov 2015 16:01:15 +1300

Changed in lightdm (Ubuntu Vivid):
status: Fix Committed → Fix Released
Changed in lightdm (Ubuntu Precise):
assignee: Robert Ancell (robert-ancell) → nobody
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