A huge security flaw in KDE/Kubuntu!

[viking_maniac]

I got more or less shocked today while I was making an extra account for private use. This is where I'm going to work with very personal and private data about me and my work, so if I need to go away from the computer, I'll either lock the session or switch to my default account until I get back. Or Especially if someone needs to access my computer for a short while.

While either locking the screen/session, or switching between the accounts, normally you should see a completely black screen with only the password prompt window in the middle. This I remember from Gnome/Ubuntu.

In KDE/Kubuntu, sometimes a bug hits the system so the screen of the session that you're about to log back into reveals the whole desktop in the background, and some corrupt graphics is shown around the login and password field. There's no problem logging back in again, but man, anyone can just give that a try, and even without a password, they'll get a perfect glance of the active desktop while the password is being prompted; this could reveal every open document on that desktop.

I'm pretty sure that this is a bug in KDE/Kubuntu, since this is related to the KDE lockout/user switch session manager only. I actually did like KDE/Kubuntu a lot; until I discovered this flaw. I can live with bugs here and there, but this is actually a major security breach in a multiuser environment; at least if you care about and need your privacy.

But before I ditch it for Gnome and get back to the good old and boring Ubuntu again, I'd like to have some opinions about this and check if this could be solved in any way. As I said, I wold like to stay and use KDE/Kubuntu, but not with this security flaw hanging over me like a ghost!

Thanks for understanding!

[Tynach]

Re: A huge security flaw in KDE/Kubuntu!

Well, actually it should show the screensaver in the background. Before I downloaded all the screensavers, though, it showed a blank screen...

Perhaps your screensaver captures the desktop, and does glitchy things to it? I'd change to a different screensaver and see if the problem persists. It could also be a graphics driver error (though I have an nVidia card, and in 9.10 I haven't had ANY issues (and I did in 9.04 with KDE 4.3.2)).

[vinnywright]

Re: A huge security flaw in KDE/Kubuntu!

OK so to test this I made a new user witch it seams would be a good idea for testing a default Karmic desktop for pepole ......like now sence my curent desktop is kind of custamised and hase kept all it's setings sence Jaunty thrue the upgrade.

it would seame that a default acount hase permishons that alowe the vewing of your files by eney one on the system and my new acct. could hapeley look at all MY files (O no).

so I go back and chang the permishons on /home/vinny so others are forbidon (no comand line all dolphin) and log back in to vinny2 now vinny2 is not alowd to look at vinny's stuff

as far as seeing the desktop wile EATHER loging in and out or lock screen and switch user I have a black background and never see a desktop wile switching!!

but I will enable a screensaver later and see if that makes a diff

VINNY

[Telengard]

Re: A huge security flaw in KDE/Kubuntu!

it would seame that a default acount hase permishons that alowe the vewing of your files by eney one on the system and my new acct. could hapeley look at all MY files (O no).

This one is perplexing, and I've also wondered about it for some time. I just assume that the Kubuntu team as a really good reason for setting permissions this way. I guess, maybe if you forgot your password to your default account and need to get your home directory copied to a new account (only a guess.)

[Tynach]

Re: A huge security flaw in KDE/Kubuntu!

Probably because both accounts will (by default) be able to use Sudo. And as root, you can see ANY file.

I say, if you don't want ANYONE else to see your home directory, encrypt it. Kubuntu supports that.

[dibl]

Re: A huge security flaw in KDE/Kubuntu!

even without a password, they'll get a perfect glance of the active desktop while the password is being prompted; this could reveal every open document on that desktop.

I'm pretty sure that this is a bug in KDE/Kubuntu, since this is related to the KDE lockout/user switch session manager only. I actually did like KDE/Kubuntu a lot; until I discovered this flaw. I can live with bugs here and there, but this is actually a major security breach in a multiuser environment

Well, thanks for registering on KFN today, so you could alert us to this situation.

I'm not qualified as a security expert, so this is just a two-bit opinion, but I'm not sure a "glance at the desktop" is exactly what they mean when they say "major security flaw". Usually I think they mean the ability to actually do something, like copy off your account number or something like that.

Since we know about it now, it seems it would be wise to actually close our working private files and desktop windows (at least the ones with our private data showing), prior to leaving the session or changing logins, right?

[Telengard]

Re: A huge security flaw in KDE/Kubuntu!

Since we know about it now, it seems it would be wise to actually close our working private files and desktop windows (at least the ones with our private data showing), prior to leaving the session or changing logins, right?

Or just press CTRL+ALT+D followed by CTRL+ALT+L before leaving the terminal.

As Tynach already suggested, I think selecting a properly working screensaver may solve the OP's problem.

[Tynach]

Re: A huge security flaw in KDE/Kubuntu!

Just another solution:

Switch to a different virtual desktop, and everyone will see a blank desktop when they see your whole desktop. Just takes one extra mouse click (on the pager) before you lock the screen.

[vinnywright]

Re: A huge security flaw in KDE/Kubuntu!

Probably because both accounts will (by default) be able to use Sudo. And as root, you can see ANY file.

I say, if you don't want ANYONE else to see your home directory, encrypt it. Kubuntu supports that.

no ser that's not true..... onley the acct. that you made when you instaled can use sudo by default the user I made with system setings>advanced>user management can NOT nor can it install eneything or see my files now that I changed the prmishons on my /home/vinny DIR.

but it is true that if you can boot a livecd you can look at eneything. on the box

VINNY

[kubicle]

Re: A huge security flaw in KDE/Kubuntu!

@viking_maniac
I couldn't quite tell whether you were joking or serious, but decided you were seriously concerned (although the thread title is sensationalist, as this cannot really be described as a security issue... much less a huge one)

Your issue (I concur with previous posters that it's likely graphics driver glitch, haven't seen it myself) does have some minor privacy implications. Although, if you leave your computer unwatched or even worse let other people use it, your private files aren't safe in any case unless you use encryption.

To avoid any possibility of anyone sneaking a peek of your desktop, I'd recommend logging out rather than just locking the session (you can also try the other measures mentioned in this thread).

Probably because both accounts will (by default) be able to use Sudo. And as root, you can see ANY file.

By default, only the first (installing) user is put in the admin group (and can use sudo), not subsequently created users.

[Tynach]

Re: A huge security flaw in KDE/Kubuntu!

Ah, I didn't know that others created after were not put into the sudoers group... I always put them in that group.

In Ubuntu, what I would do is instead of log out or whatever, I'd just pop up a guest session and let them play around. Is there an equivalent to that in Kubuntu?

[Snowhog]

Re: A huge security flaw in KDE/Kubuntu!

Just create a new user - Guest - give it a password of your choosing (guest) and then assign/remove the groups that you want for this user.

[Tynach]

Re: A huge security flaw in KDE/Kubuntu!

Well, yeah, but the Ubuntu guest account seems to always go back to default, and (at least, I don't think) won't allow you to permanently save files... Basically, as if it's an account that gets wiped at logout.

I want something like that.

[viking_maniac]

Re: A huge security flaw in KDE/Kubuntu!

Well, maybe the thread title is a bit overstated, but some people lock their desktop for a reason. And what's the point of locking it if it doesn't work?

This bug, or whatever it is, is actually not a very good reason to ditch KDE IMO, so I'll try to work my way around it. I've done a lot of testing and stuff on this install since I'm only testing Kubuntu at this point. I'll make a clean install sooner or later, so we'll see what happens after that.

I'll try to stick with KDE as long as possible, since I really love it!

Thanks for your feedback! And I'll test out your suggestions!

BTW, are there any third-party screen lockout programs in the repository? Or any other privacy enhancing tools?

Thanks!

[viking_maniac]

Re: A huge security flaw in KDE/Kubuntu!

it would seame that a default acount hase permishons that alowe the vewing of your files by eney one on the system and my new acct. could hapeley look at all MY files (O no).

I've made, and I always make, my important documents, or whatever is private, read only for my main account.