It's possible to bypasss lockscreen if user is in nopasswdlogin group.

Bug #1413790 reported by Andrea Azzarone on 2015-01-22
22
This bug affects 3 people
Affects Status Importance Assigned to Milestone
Unity
Fix Released
Medium
Andrea Azzarone
7.2
In Progress
Medium
Stephen M. Webb
unity (Ubuntu)
Medium
Andrea Azzarone
Nominated for Trusty by Stephen M. Webb
Trusty
Medium
Stephen M. Webb

Bug Description

[IMPACT]
A user is presented with a password dialog even if a member of the nopasswdlogin group (and may not have a password).

[TEST CASE]

(1) Create a test user.
(2) Add the test user to the nopasswdlogin group.
(3) Log in to a Unity session using that acocunt.
(4) Lock the screen.
(5) Attempt to unlock the screen: no password prompt should be presented.

[REGRESSION POTENTIAL]

Conceivably allowing a login with no authentication could present unexpected vulnerabilities in which unforseen code paths also exercise this function. Care has been taken by the developer to avoid such cases.

[OTHER INFO]

The fix for Ubuntu 14.04 LTS was cherry picked from the Ubuntu "Vivid Vervet" dev release where it has been in production use for some time without apparent regression.

Related branches

Andrea Azzarone (azzar1) on 2015-01-22
no longer affects: unity (Ubuntu)
description: updated
Andrea Azzarone (azzar1) wrote :

Not sure who's emitting the "unlock" signal: lightdm or gnome-session or what?

Andrea Azzarone (azzar1) on 2015-01-23
summary: - Lightdm should not emit logind "unlock" signal when the user is in
- nopasswdlogin group.
+ It's possible to bypasss lockscreen if user is in nopasswdlogin group.
Andrea Azzarone (azzar1) on 2015-01-23
no longer affects: gnome-session (Ubuntu)
Changed in unity:
milestone: none → 7.3.1
assignee: nobody → Andrea Azzarone (andyrock)
Changed in unity (Ubuntu):
assignee: nobody → Andrea Azzarone (andyrock)
Changed in unity:
status: New → In Progress
Changed in unity (Ubuntu):
status: New → In Progress
Marc Deslauriers (mdeslaur) wrote :

I'm not sure there is a security issue here.

Being in the noasswdlogin group means you can login without a password.
Currently, the lock screen _does_ ask for a password, which is possibly contrary to expectations, since anyone can step up to the computer and simply reboot it.

I believe the bug is actually the fact that the lock screen does ask for a password.

Marc Deslauriers (mdeslaur) wrote :

In fact, the User Accounts applet in the Settings allows creating a user with no password by putting it in the nopasswdlogin group, but as soon as the screen lock comes up, the user is unable to unlock the screen.

So the screen lock definitely needs to honour the nopasswdlogin group, and this is a bug with no real security implications.

information type: Private Security → Public
Andrea Azzarone (azzar1) on 2015-01-23
Changed in lightdm (Ubuntu):
status: New → Invalid
Changed in lightdm:
status: New → Invalid
no longer affects: lightdm (Ubuntu)
no longer affects: lightdm
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package unity - 7.3.1+15.04.20150126-0ubuntu1

---------------
unity (7.3.1+15.04.20150126-0ubuntu1) vivid; urgency=low

  [ Andrea Azzarone ]
  * Force icon size (new gtk requires it). (LP: #1404730)
  * Disable markup accel for VolumeLauncherIcon quicklist menu items.
    (LP: #1413411)
  * Make sure dragged icons are not rendered behind the dash. (LP:
    #1413773)
  * Make unity unlockable if user is in nopsswdlogin group. On super+l
    the screensaver is activated. (LP: #1413790)
 -- Ubuntu daily release <email address hidden> Mon, 26 Jan 2015 22:42:26 +0000

Changed in unity (Ubuntu):
status: In Progress → Fix Released
Andrea Azzarone (azzar1) on 2015-01-28
Changed in unity:
status: In Progress → Fix Committed
Stephen M. Webb (bregma) on 2015-02-11
Changed in unity:
status: Fix Committed → Fix Released
Stephen M. Webb (bregma) on 2015-03-11
Changed in unity:
importance: Undecided → Medium
Changed in unity (Ubuntu):
importance: Undecided → Medium
Stephen M. Webb (bregma) on 2015-03-18
Changed in unity (Ubuntu Trusty):
status: New → In Progress
importance: Undecided → Medium
assignee: nobody → Stephen M. Webb (bregma)
description: updated

Hello Andrea, or anyone else affected,

Accepted unity into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/unity/7.2.4+14.04.20150316-0ubuntu1 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 unity (Ubuntu Trusty):
status: In Progress → Fix Committed
tags: added: verification-needed
tags: added: verification-done
removed: verification-needed
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package unity - 7.2.4+14.04.20150316-0ubuntu1

---------------
unity (7.2.4+14.04.20150316-0ubuntu1) trusty; urgency=medium

  [ Andrea Azzarone ]
  * Avoid running potentially dangerous code paths when the screen is
    locked. (LP: #1410582)
  * Ungrab the shoutdown dialog as soon as possible. (LP: #1398287)
  * Use COMPIZ_METAKEY where needed. (LP: #1363534)
  * disabled Pointer Barriers during lockscreen (LP: #1401911)
  * disabled markup for VolumeLauncherIcon quicklist menu items (LP:
    #1413411)
  * enable Dash, Hud, and session dialogs over full screen window (LP:
    #1159249, #860970, #1413773, #1404486)
  * made unity unlockable if user is in nopsswdlogin group (LP:
    #1413790)
  * skipped the animation of BGHash on startup to prevent unwanted fade-
    in (LP: #1241757)

  [ Luke Yelavich ]
  * extended accessible exploration of the Dash dynamic content (LP:
    #1066157)

  [ Marco Trevisan (Treviño) ]
  * MenuManager: make sure menus are always shown when mouse is over
    them or when the always-show-menus option is on (LP: #955193,
    #1390562, #1374942, #1312137)
  * PanelService: use gdbus to notfy upstart of service start/stop (LP:
    #1302955)
 -- CI Train Bot <email address hidden> Mon, 16 Mar 2015 17:30:35 +0000

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

The verification of the Stable Release Update for unity 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.

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