sddm-greeter crashes with segfault (Bad RIP value) before login shows up on Lubuntu 20.04.2 LTS

[Kerem Gümrükcü]

After installing the latest Lubuntu 20.04.2 LTS on my laptop, i wasnt able to log on into that system anymore. The system runs into a mouse cursor only visible black screen with no greeter to log in. Switching to console and login into terminal is just fine and all works as expected on terminal level. Restarting the sddm (service sddm restart) didnt work. Reinstalling/reconfiguring (purging orphaned conf file before) sddm and lubuntu-desktop didnt help. After some investigation on the log files, i found out that the sddm-greeter process crashes for reasons unknown with a bad instruction pointer value. More info below.

dmesg:
[71.601020] sddm-greeter[1084]: segfault at 0 ip 0000000000000000 sp 00007ffe946a7ed8 error 14 in sddm-greeter[55bc43ab0000+17000]
[71.601030] Code: Bad RIP value.

System Arch:
amd64

lsb_release -a:
Distributor ID: Ubuntu
Description: Ubuntu 20.04.2 LTS
Release: 20.04
Codename: focal

uname -r:
5.4.0-66-generic

apt-cache show sddm:
Package: sddm
Architecture: amd64
Version: 0.18.1-1ubuntu2
Priority: optional
Section: universe/kde
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: Debian/Kubuntu Qt/KDE Maintainers <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 1916
Provides: x-display-manager
Depends: adduser, qml-module-qtquick2, xauth, x11-common, xserver-xorg | xserver, debconf (>= 0.5) | debconf-2.0, libc6 (>= 2.14), libgcc-s1 (>= 3.0), libpam0g (>= 0.99.7.1), libqt5core5a (>= 5.12.2), libqt5dbus5 (>= 5.6.0~), libqt5gui5 (>= 5.6.0~beta) | libqt5gui5-gles (>= 5.6.0~beta), libqt5network5 (>= 5.6.0~), libqt5qml5 (>= 5.0.2), libqt5quick5 (>= 5.0.2) | libqt5quick5-gles (>= 5.0.2), libstdc++6 (>= 5.2), libsystemd0, libxcb-xkb1, libxcb1
Recommends: haveged, libpam-systemd, sddm-theme-debian-maui | sddm-theme
Suggests: libpam-kwallet5, qtvirtualkeyboard-plugin
Filename: pool/universe/s/sddm/sddm_0.18.1-1ubuntu2_amd64.deb
Size: 631728
MD5sum: 7926cf1daefe2f0d730dd592342d15c1
SHA1: 4d37b7b88160a7fd2235c7fd296cdbeb1d042a91
SHA256: e894e61102080f66e397eb462d418a7c490ac91e0499d3becbf0a8011bd0a429
Homepage: https://github.com/sddm/sddm
Description-en: modern display manager for X11
 SDDM is a modern display manager for X11 aiming to be fast, simple
 and beautiful. It uses modern technologies like QtQuick to create
 smooth, animated user interfaces.
Description-md5: 60d2ea934d7c99b8460547a3b6ef2196
Task: kubuntu-desktop, kubuntu-full, lubuntu-desktop

[Chris Guiver (guiverc)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:

apport-collect 1916670

When reporting bugs in the future please use apport by using 'ubuntu-bug' and the name of the package affected. You can learn more about this functionality at https://wiki.ubuntu.com/ReportingBugs.

[Launchpad Janitor (janitor)]

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