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Date: Tue, 10 Nov 2020 14:12:49 -0500
From: "Demi M. Obenour" <demiobenour@...il.com>
To: "Vladimir D. Seleznev" <vseleznv@...linux.org>,
oss-security@...ts.openwall.com
Subject: Re: The importance of mutual authentication: Local
Privilege Escalation in X11
On 11/10/20 1:43 PM, Vladimir D. Seleznev wrote:
>>> This contravenes the ability to run X11 client from another user. The
>>> idea is that X11 server allows any clients with right credentials
>>> regardless of theirs processes UID or GID to connect to the server.
>> Indeed it does, and I mention cryptographic authentication mechanisms
>> below. Instead of /tmp, /run/X11 would work just as well. It is
>> the mutual authentication that matters.
> Do I understand you correctly: you propose to forbid running X11 clients
> which processes belong to another users? In that case it is a bad idea:
> I would like to run untrusted clients with special UIDs. Or if I
> understand you wrongly, please explain how client of other user can
> connect to the socket placed in /run/user/$UID with these strict access
> permissions 0700?
If you aren’t using the X Security Extension or the X Access
Control Extension, then X clients aren’t effectively isolated from
each other. Therefore, connecting untrusted X clients to the desktop
session is a bad idea.
Under my proposal, you would still be able to run an X server with
cryptographic authentication, but it would be more secure than it
is today. Depending on the display manager, you might need to run
your own X server.
Sincerely,
Demi
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