For an article written late last year I hoped for a little more awareness of how massive a security hole granting full, unfiltered access to the X11 server is. Granted, any sandboxing is better than none, but firefox is one of the few apps that already sandboxes itself really well, and with a blog title like that it might be good to touch upon things like nested X servers such as Xephyr.
> Xeyes is cute until one considers the practical implications…
what's the problem with xeyes? it reads data on your computer and displays it. Just like vim or cat.
If, for some reason, you want to run a program that you don't trust, you should sandbox it from the outside. But granting full rights to distro-provided programs like vim or xeyes is perfectly sane. Just like you trust your kernel.
> But granting full rights to distro-provided programs like vim or xeyes is perfectly sane
Saying this after the whole XZ utils ordeal has happened is quite interesting.
Can you really guarantee that your distro is not compromised? And if it is compromised, how can you easily _discover_ that a program is doing something strange?
X11 (the one that most people are familiar with, not the locked down one with X security -- because the latter introduces compatibility issues) does not have an access control model where programs can request for specific permissions.
In other words, xeyes would just work(TM) without the user granting it permission to read global mouse pointer position. And simultaneously, the same is true for $compromised_distro_provided_program.
It is the same issue with all sandboxing solutions. If your program does not work without giving it excessive permissions, it does not work. If we want to move to a version with minimal privileges, X would still seem like a good platform to work on this. But one would have to work on it, not decide that everything needs to be rewritten all the time.
1 malicious package almost got distributed in 20 years of debian history?
>granting full rights to vim or xeyes
I'm not sure I get what's being discussed here. Standard Xorg runs without root already. And Xeyes definitely 100% run without root, I get why you would you run vim on root, to edit root files, but also don't? Especially if you have plugins, run simple programs like echo>> , ed, grep or nano.
> But granting full rights to distro-provided programs like vim or xeyes is perfectly sane.
You mean run everything distro-provided as root?
There are reasons systems don't do that any more. Even distro-provided services are often setup in a way to no run with full rights. Can you imaging reasons why this is done?
What was neglected is doing the same on user level, which should be done for pretty much the same reasons.
Correct me if I'm wrong, but passing through the X socket gives a giant sandbox escape as any application can control/see any other application, including a root terminal in a GUI app.
Most of the time applications can read each other's memory, so protecting the display does not make much sense.
Basic X client isolation (not using XACE just Xsecurity) would have worked for sandboxed applications with some minor changes (allowing access to some basic modern extensions, I had a local patch for this once). There is really not fundamental issue in X that could now allow isolation of clients.
It is my understanding that XACE doesn't actually provide any security features itself. It just provides the "hooks" to implement security extensions. Like LSM feature in Linux kernel. You have to install a additional X11 extension to do something useful with it.
So the most common X11 security extension is going to be xcsecurity which enables the SECURITY extension. It allows a course permission model were applications can be designated as "Trusted" or "Untrusted". That is going to show up in many Linux distributions.
However all applications default to "trusted" because if they are untrusted they tend to cause lots of other annoying problems and crashes a lot of apps, apparently.
In practice the only place it shows up is if you are using "ssh -X". That uses the security extension by default. Which is why there is also a "ssh -Y" that disables it for applications that it breaks.
This sort of thing is why to fix X11 security you have to give up backwards compatibility and create a new X version.
Oh, wait, that is what the X developers did with Wayland.
> In practice the only place it shows up is if you are using "ssh -X". That uses the security extension by default. Which is why there is also a "ssh -Y" that disables it for applications that it breaks.
Unless your distro changes the default to make "ssh -X" and "ssh -Y" behave the same which popular distributions do.
for example standardized window management, left as an exercise to the GUI lib and the compositor? and woop woop X11 GUI apps need to be rewritten to support window management on WSL (Wayland based) and the network reconnect on hybernate also broke.
This is rather incomplete. For instance, gtk devs already threw out tons of old code in GTK4. Wayland also has fewer features than xorg; and there are also fewer choices available. I noticed this with regards to WMs/DEs. I am not even going to issues wayland has with regards to certain video graphics - that's another not mentioned issue here.
You are trying to pick individual cherries.
> This sort of thing is why to fix X11 security you have to give up backwards compatibility and create a new X version.
Let's have a look in a little while. I myself hope for better and more transparent information at all times. Probably others want better security overall. Would it not be somewhat interesting if wayland were to be abandoned eventually due to having too few useful features compared to xserver?
> Wayland also has fewer features than xorg; and there are also fewer choices available
Because Wayland is a strictly a window management protocol focused on policy over mechanism.
> I am not even going to issues wayland has with regards to certain video graphics - that's another not mentioned issue here.
We also aren't going to mention issues Xorg or XLibre have with some graphics setups, because that's neither here nor there. This is a thread about security.
> I don't think so: <XLibre github repo link>
Didn't XLibre break some applications when launched?
> Would it not be somewhat interesting if wayland were to be abandoned eventually due to having too few useful features compared to xserver?
It would be interesting to see Wayland abandoned for a better protocol/set of protocols, xserver is neither a protocol nor really better.
The problem is that Wayland just isn't a compelling alternative for many people, so they don't move. For me, I see no benefit because I got used to avoiding HiDPI and don't have a mixed-DPI workspace. For some bizarre reason they made each compositor implement input-handling separately, so for example artists might have to switch compositor just to use their tablet of choice. And worse yet, some people with input accessibility needs are just going to get straight up locked out of libre computing. See https://nocoffei.com/?p=451 for one example.
In the end Red Hat failed to kill off X11. Let's see what happens next. The
GTK devs already rejected patches for maintaining the toolkit further for the
xorg platform, following their "GTK5 will no longer support x11" agenda. Would be kind of great to have a universal GUI toolkit that would
work rather than have toolkits controlled de-facto by private companies who just willy-nilly throw out support for this or that platform at their own selfish discretion. Though,
someone else now helps maintain gtk2, though most of the patches are in regards to
fixing bugs, ensuring that it can be compiled and so forth. https://git.devuan.org/Daemonratte/gtk2-ng
I wish I lived in a world were you didn't have to sign contracts, lock your doors, or have X11 security. It is so fun to run xmeltdown a new user's display.
Hard for me to take that one seriously.. For example they call out byte swapping for endianness as the type of cruft holding back X11. Such a trivial thing to be concerned enough to put in the readme... (I guess Phoenix is also putting this..) Seems like mostly authored by Claude too.
This is a problem in many projects now. xserver and mruby for instance also succumbed to claude. It seems claude is the ultimate virus. It leaks into almost every project now. So I am not sure it can be used as differentiating criterium here merely for being claude AI slop. I've noticed a lot of documentation is now totally useless though; claude slop is just unreadable to me. It's like a person who is not able to think, wrote the documentation. I did not have this issue back when real humans wrote documentation, even though high quality documentation was always rare anyway. But, for instance, Jeremy Evans in his projects tends to write high-quality documentation in general, and I can understand it fine, whereas if you look at matz spinel, I have no idea what the AI slop in the README is really trying to convey. Or on ffmpeg, a german dev used AI slop to try to create some proposal, and someone else pointed out that this is pointless and impossible to read and understand, yet the original guy did not understand why real people don't want to be AI slop spammed. It's very strange.
For an article written late last year I hoped for a little more awareness of how massive a security hole granting full, unfiltered access to the X11 server is. Granted, any sandboxing is better than none, but firefox is one of the few apps that already sandboxes itself really well, and with a blog title like that it might be good to touch upon things like nested X servers such as Xephyr.
Yeah, sadly Firefox and Chrome want almost full privileges so that they can sandbox themselves.
X itself always bothers me. Xeyes is cute until one considers the practical implications…
> Xeyes is cute until one considers the practical implications…
what's the problem with xeyes? it reads data on your computer and displays it. Just like vim or cat.
If, for some reason, you want to run a program that you don't trust, you should sandbox it from the outside. But granting full rights to distro-provided programs like vim or xeyes is perfectly sane. Just like you trust your kernel.
> But granting full rights to distro-provided programs like vim or xeyes is perfectly sane
Saying this after the whole XZ utils ordeal has happened is quite interesting.
Can you really guarantee that your distro is not compromised? And if it is compromised, how can you easily _discover_ that a program is doing something strange?
X11 (the one that most people are familiar with, not the locked down one with X security -- because the latter introduces compatibility issues) does not have an access control model where programs can request for specific permissions.
In other words, xeyes would just work(TM) without the user granting it permission to read global mouse pointer position. And simultaneously, the same is true for $compromised_distro_provided_program.
It is the same issue with all sandboxing solutions. If your program does not work without giving it excessive permissions, it does not work. If we want to move to a version with minimal privileges, X would still seem like a good platform to work on this. But one would have to work on it, not decide that everything needs to be rewritten all the time.
> the whole XZ ordeal
1 malicious package almost got distributed in 20 years of debian history?
>granting full rights to vim or xeyes
I'm not sure I get what's being discussed here. Standard Xorg runs without root already. And Xeyes definitely 100% run without root, I get why you would you run vim on root, to edit root files, but also don't? Especially if you have plugins, run simple programs like echo>> , ed, grep or nano.
> until one considers the practical implications
You failed at that step.
The practical implication is that every other X11 app can also read your input even when it's not in the foreground.
> But granting full rights to distro-provided programs like vim or xeyes is perfectly sane.
You mean run everything distro-provided as root?
There are reasons systems don't do that any more. Even distro-provided services are often setup in a way to no run with full rights. Can you imaging reasons why this is done?
What was neglected is doing the same on user level, which should be done for pretty much the same reasons.
Correct me if I'm wrong, but passing through the X socket gives a giant sandbox escape as any application can control/see any other application, including a root terminal in a GUI app.
No, X11 supports pretty detailed per-application access control, similar to selinux (XACE).
The author of the phoenix x server has blogged about it, iirc.
> XACE
Which is configured by default on what distros?
Most of the time applications can read each other's memory, so protecting the display does not make much sense.
Basic X client isolation (not using XACE just Xsecurity) would have worked for sandboxed applications with some minor changes (allowing access to some basic modern extensions, I had a local patch for this once). There is really not fundamental issue in X that could now allow isolation of clients.
Nowhere (and everywhere).
It is my understanding that XACE doesn't actually provide any security features itself. It just provides the "hooks" to implement security extensions. Like LSM feature in Linux kernel. You have to install a additional X11 extension to do something useful with it.
So the most common X11 security extension is going to be xcsecurity which enables the SECURITY extension. It allows a course permission model were applications can be designated as "Trusted" or "Untrusted". That is going to show up in many Linux distributions.
However all applications default to "trusted" because if they are untrusted they tend to cause lots of other annoying problems and crashes a lot of apps, apparently.
In practice the only place it shows up is if you are using "ssh -X". That uses the security extension by default. Which is why there is also a "ssh -Y" that disables it for applications that it breaks.
This sort of thing is why to fix X11 security you have to give up backwards compatibility and create a new X version.
Oh, wait, that is what the X developers did with Wayland.
> In practice the only place it shows up is if you are using "ssh -X". That uses the security extension by default. Which is why there is also a "ssh -Y" that disables it for applications that it breaks.
Unless your distro changes the default to make "ssh -X" and "ssh -Y" behave the same which popular distributions do.
except Wayland dropped the baby with the bathtub?
for example standardized window management, left as an exercise to the GUI lib and the compositor? and woop woop X11 GUI apps need to be rewritten to support window management on WSL (Wayland based) and the network reconnect on hybernate also broke.
But at least Games are faster, aren't they...
> that is what the X developers did with Wayland
This is rather incomplete. For instance, gtk devs already threw out tons of old code in GTK4. Wayland also has fewer features than xorg; and there are also fewer choices available. I noticed this with regards to WMs/DEs. I am not even going to issues wayland has with regards to certain video graphics - that's another not mentioned issue here.
You are trying to pick individual cherries.
> This sort of thing is why to fix X11 security you have to give up backwards compatibility and create a new X version.
I don't think so: https://github.com/X11Libre/xserver
Let's have a look in a little while. I myself hope for better and more transparent information at all times. Probably others want better security overall. Would it not be somewhat interesting if wayland were to be abandoned eventually due to having too few useful features compared to xserver?
> Wayland also has fewer features than xorg; and there are also fewer choices available
Because Wayland is a strictly a window management protocol focused on policy over mechanism.
> I am not even going to issues wayland has with regards to certain video graphics - that's another not mentioned issue here.
We also aren't going to mention issues Xorg or XLibre have with some graphics setups, because that's neither here nor there. This is a thread about security.
> I don't think so: <XLibre github repo link>
Didn't XLibre break some applications when launched?
> Would it not be somewhat interesting if wayland were to be abandoned eventually due to having too few useful features compared to xserver?
It would be interesting to see Wayland abandoned for a better protocol/set of protocols, xserver is neither a protocol nor really better.
Is X11 going to be like IE6. Still around in another 10 years after it was intended to be deprecated across all major distros (2025/2026).
The problem is that Wayland just isn't a compelling alternative for many people, so they don't move. For me, I see no benefit because I got used to avoiding HiDPI and don't have a mixed-DPI workspace. For some bizarre reason they made each compositor implement input-handling separately, so for example artists might have to switch compositor just to use their tablet of choice. And worse yet, some people with input accessibility needs are just going to get straight up locked out of libre computing. See https://nocoffei.com/?p=451 for one example.
> I like my cozy Plasma DE [...] clean, all free of ads and bad UI redesigns and AI injected into every corner.
Plasma itself is an example of bad UI redesign (but a far cry from Gnome).
It's gonna be like ipv4. Still around in a thousand years.
X11 fine
Youngins just don't wanna learn it
Is wayland going to be aroud in another 10 years, or it it the new pulseaudio?
I don't think it is "just around" - it is actively maintained still:
https://github.com/X11Libre/xserver
In the end Red Hat failed to kill off X11. Let's see what happens next. The GTK devs already rejected patches for maintaining the toolkit further for the xorg platform, following their "GTK5 will no longer support x11" agenda. Would be kind of great to have a universal GUI toolkit that would work rather than have toolkits controlled de-facto by private companies who just willy-nilly throw out support for this or that platform at their own selfish discretion. Though, someone else now helps maintain gtk2, though most of the patches are in regards to fixing bugs, ensuring that it can be compiled and so forth. https://git.devuan.org/Daemonratte/gtk2-ng
Real question: is X11Libre widely used by anyone but its maintainers?
Several distros have gone XLibre as their default display manager. I installed Artix on a bc-250 just last week and XLibre was the default there.
See also yserver[0]: A modern X11 server written from scratch in Rust.
0: https://github.com/joske/yserver
Putting apps in a container sounds like a great idea until you need to access your files.
Or until you realize X11 is one giant escape hatch. You might not have (convenient) access to your files but the attacker does.
In terms of attack surface, how does this compare to just using AppArmor or SELinux, without containers?
I wish I lived in a world were you didn't have to sign contracts, lock your doors, or have X11 security. It is so fun to run xmeltdown a new user's display.
Or one could just use firejail, which comes with a number of pre made profiles for common applications.
The sandbox command works well on systems using SELinux.
https://docs.redhat.com/en/documentation/red_hat_enterprise_...
This is a great article.
I have little experience with lxc but I guess waypipe could be an option too.
Xlibre (the only current actively developed implementation of a X11 server) has a new extension - XNamespace to address some challenges as well.
https://github.com/X11Libre/xserver/blob/master/doc/Xnamespa...
Not the only one, there's also a new one (written in zig) I've forgot the name of.
edit: phoenix was the name: https://github.com/external-mirrors/phoenix#phoenix
There's also this new one: https://github.com/joske/yserver
Hard for me to take that one seriously.. For example they call out byte swapping for endianness as the type of cruft holding back X11. Such a trivial thing to be concerned enough to put in the readme... (I guess Phoenix is also putting this..) Seems like mostly authored by Claude too.
> Seems like mostly authored by Claude too.
This is a problem in many projects now. xserver and mruby for instance also succumbed to claude. It seems claude is the ultimate virus. It leaks into almost every project now. So I am not sure it can be used as differentiating criterium here merely for being claude AI slop. I've noticed a lot of documentation is now totally useless though; claude slop is just unreadable to me. It's like a person who is not able to think, wrote the documentation. I did not have this issue back when real humans wrote documentation, even though high quality documentation was always rare anyway. But, for instance, Jeremy Evans in his projects tends to write high-quality documentation in general, and I can understand it fine, whereas if you look at matz spinel, I have no idea what the AI slop in the README is really trying to convey. Or on ffmpeg, a german dev used AI slop to try to create some proposal, and someone else pointed out that this is pointless and impossible to read and understand, yet the original guy did not understand why real people don't want to be AI slop spammed. It's very strange.
XWayland is actively developed.
XFree86, which is the "standalone DDX" you see on X11 desktops, is being actively maintained.