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Trivial Bug In X.Org Server Gives Root Permissions On Linux, BSD Systems (bleepingcomputer.com)
An anonymous reader quotes a report from Bleeping Computer: A vulnerability that is trivial to exploit allows privilege escalation to root level on Linux and BSD distributions using X.Org server, the open source implementation of the X Window System that offers the graphical environment. The flaw is now identified as CVE-2018-14665 (credited to security researcher Narendra Shinde). It has been present in xorg-server for two years, since version 1.19.0 and is exploitable by a limited user as long as the X server runs with elevated permissions.
An advisory on Thursday describes the problem as an "incorrect command-line parameter validation" that also allows an attacker to overwrite arbitrary files. Privilege escalation can be accomplished via the -modulepath argument by setting an insecure path to modules loaded by the X.org server. Arbitrary file overwrite is possible through the -logfile argument, because of improper verification when parsing the option. Apart from OpenBSD, other operating systems affected by the bug include Debian and Ubuntu, Fedora and its downstream distro Red Hat Enterprise Linux along with its community-supported counterpart CentOS.
An advisory on Thursday describes the problem as an "incorrect command-line parameter validation" that also allows an attacker to overwrite arbitrary files. Privilege escalation can be accomplished via the -modulepath argument by setting an insecure path to modules loaded by the X.org server. Arbitrary file overwrite is possible through the -logfile argument, because of improper verification when parsing the option. Apart from OpenBSD, other operating systems affected by the bug include Debian and Ubuntu, Fedora and its downstream distro Red Hat Enterprise Linux along with its community-supported counterpart CentOS.
Your comment is funnier than you think since logind which part of the systemd project allows for X.Org to run rootless which completely avoid this very issue.
It's not about having Xorg being run as root (which is probably the case if you run an X display manager), but about the ability for a user to launch Xorg with root privileges (with the setuid bit).
On my Debian stretch, Xorg is not setuid, so there's no privilege escalation.
FTFA:
As a temporary solution, users can disable the Xorg binary by running the following command: /usr/X11R6/bin/Xorg
chmod u-s
Seriously, that guy is an idiot. Obviously doesn't understand what's a setuid bit and copy/pasting command lines as if it they were magic spells.
I have discovered a truly marvelous proof of killer sig, which this margin is too narrow to contain.
The X server doesn't need direct access to the "graphics chipsets" (eg. the GPU). It is designed to run over network connections.
You've got it backwards, probably because of the unfortunate and counter-intuitive terminology they use.
The X server shows the graphics on the local terminal (which is usually the "client" hardware), and the X client is the interface used by the software application that can be running remotely (which is often on the "server" hardware). So the X server does need to access the GPU.
OK, it's more nuanced than that. The Xorg server isn't suid, but there is an Xorg.wrap binary that is suid, which provides xstart/xinit functionality from a physical console. So not exploitable remotely, e.g., ssh, but shared public Linux machines are vulnerable. Those would be rare, but admins better move to get them updated. Debian already has fixes except for buster.
When all you have is a hammer, every problem starts to look like a thumb.