Red Hat Bugzilla – Bug 517772
Fast-user-switching leaves virtual terminals insecure.
Last modified: 2011-06-27 10:20:45 EDT
Description of problem:
When switching between virtual terminals using F11's Fast-User-Switching, under certain conditions you may freely switch between logins without ever being prompted to unlock the screen or enter a password.
All the time.
Steps to Reproduce:
1. Make two user accounts on a Fedora system, A & B.
2. Login to A.
3. Fast-user-switch to B.
4. Virtual-console-switch back to A (using shortcut form of Ctrl+Alt+F7, etc.)
5. Unlock A.
6. Virtual-console-switch to B. Notice that B does not prompt you for a password.
You may now freely virtual-console-switch without ever being prompted for a password.
When switching between open users, you should always be prompted for a password.
It appears that the current terminal is locked when "Switch User" from applet or logout menu is used.
The problem is that when virtual-console-switching AWAY from a terminal, that terminal is not locked. You may then switch back to it without entering a password.
IE, accounts are only safely locked if you switch away using "Switch User."
1. Somehow, detect when the virtual-console is switched, and lock the terminal that the user leaves.
2. Disable graphical virtual-console-switching. (IE, the -only- way to switch becomes "Switch User" in logout or user-applet, which safely locks the screen).
Generally speaking, it's quite common, but the mere idea of virtual-console-switching is insecure, even in text mode.
It is rather outrageous to disable the text-mode virtual consoles, since these have quite a pedigree and are useful, ex, having multiple logins of the same account (not possible under X/GDM).
However, since the graphical user-switching does not have that use-case, and free graphical-terminal-switching is insecure, it would make sense to disable virtual-console-switching for the graphical terminals.
At least for the graphical logins, you should not be able to freely switch between different accounts without being prompted for credentials. Neither Mac OS X nor Windows allow you to jump directly between different logged in virtual-terminals: they force you go back to the login screen.
Would anybody like to at least confirm this bug? It doesn't seem insignificant.
Yes, the problem is there (and it was always there even on the text console switches).
I understand it being there on the text console switches.
However, that seems to be a legacy convention with Linux. I think that's probably going to be a hard thing to change.
At least it's relatively early enough in life for the new graphical login switch to be designed in a secure manner though.
Thank you for the bug report.
Fedora Bugzappers volunteer triage team
Fedora Bugzappers volunteer triage team
This bug appears to have been reported against 'rawhide' during the Fedora 13 development cycle.
Changing version to '13'.
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