Bypass Login Screen by replugging in external monitors
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
gdm3 (Ubuntu) |
Confirmed
|
High
|
Unassigned |
Bug Description
I found a bug in ubuntu At the login screen
buster/sid
Linux 4.15.0-24-generic #26-Ubuntu SMP Wed Jun 13 08:44:47 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
I use my work laptop and today when I came back to office I connected both my external monitor.
1 HDMI cable and 1 Mini display port cable.
Then I realize one screen on the right had my login screen prompting for password and the left monitor was unlock, I was able to navigate the mouse and use the computer just fine. However all the keyboard input was sent to the password prompt.
I did the test a couple time and each time I was able to reproduce the issue.
#1: Lock the computer
#2: Disconnect both external monitor
#3: Reconnect external monitor ( my sequence was HDMI -> Display port )
#4: You've bypass the login screen.
When doing the demo to my colleague I was able to completely bypass the login screen on both screen and had complete mouse and keyboard input. At that time I was not able anymore to lock my session. I had to reboot the laptop.
Laptop model:
Manufacturer: LENOVO
Product Name: 20FN002VCA
Version: ThinkPad T460
---
ProblemType: Bug
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
DistroRelease: Ubuntu 18.04
InstallationDate: Installed on 2018-04-30 (104 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
Package: gdm3 3.28.2-0ubuntu1.3
PackageArchitec
ProcEnviron:
LANGUAGE=en_CA
TERM=xterm-
PATH=(custom, no user)
LANG=en_CA.UTF-8
SHELL=/bin/bash
ProcVersionSign
Tags: bionic
Uname: Linux 4.15.0-30-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:
_MarkForUpload: True
affects: | launchpad → gdm3 (Ubuntu) |
summary: |
- Bypass Login Screen + Bypass Login Screen by replugging in external monitors |
information type: | Private Security → Public Security |
Changed in gdm3 (Ubuntu): | |
status: | Incomplete → New |
importance: | Undecided → High |
When testing again, after the reboot I was able to bypass the login screen by just disconnecting both external monitor and had full access of the computer and input device.