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Date: Fri, 20 Oct 2023 18:21:18 +0300
From: Turistu <>
Subject: Re: with firefox on X11, any page can pastejack you

On Fri, Oct 20, 2023 at 03:27:41PM +0200, Solar Designer wrote:
> On Tue, Oct 17, 2023 at 03:17:36AM +0300, turistu wrote:
> > In firefox running on X11, any script from any page can freely write to the
> > primary selection, and that can be easily exploited to run arbitrary code
> > on the user's machine.
> What about other web browsers running on X11, most notably Chrome and
> Chromium?

They're safe from *this* particular issue, which is caused by a simple bug
deep inside mozilla's C++ code, not by some explicit design decision.

> If the issue is unique to Firefox or at least not universal
> across browsers, that's an extra reason for Firefox to make a change.
> On Fri, Oct 20, 2023 at 02:10:06AM +0300, Turistu wrote:
> > OK this was probably too technical and terse for people not familiar
> > with X11 programming and terminology, so thing goes like this:
> > 
> > 1. If you're a user who has first learned to use a GUI on e.g. Windows,
> > and who is used to copy & paste with Ctrl-C Ctrl-V (or with left-click,
> > choose Copy from the menu, and then again left-click, choose Paste),
> > then congratulations! this DOES NOT AFFECT YOU.
> > 
> > (Unless you're using some clipboard tools which merges the primary and
> > clipboard selection, but I guess you don't ;-))
> > 
> > 2. But if you're a *native* X11 user who is used to just select the text and
> > then paste it with a middle-click or shift-Insert, then this means you're
> > pretty much done, and you should immediately either stop using firefox or
> > try the workaround and patch described in my report. This also includes
> > Wayland users.
> Or isolate Firefox to its own X server (or at least a separate one from
> where you run terminal emulators managing important stuff), like it
> happens when you run it in its own VM (or perhaps many instances of it
> in many VMs) on Qubes OS.  Indeed this also removes the convenience of

If you do that, notice that you will also have to run a window manager
inside that separate X server, because firefox (which never implemented
the X11 and icccm protocols correctly) needs a wm in order to function
properly (more precisely a point-to-focus wm or one that simulates
point-to-focus just to keep firefox and some other horrors like old atk
java apps happy).

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