I'm using the 'Blank Screen' screensaver that just shows a black screen. However, sometimes when I interrupt the screen saver to log in again, it gets rid of the black screen and instead shows what is underneath it. See attached file. I can't interact with the windows it shows, and it isn't showing the windows at they currently are; I think it shows the windows as they were when the screensaver started. This usually happens only the first time I try to unlock the screen. If I wait for the login window to go away, it goes back to a black screen, and it keeps the black screen up if I try to log in again. Part of the purpose of a locked screensaver is to prevent people from seeing what's underneath the screensaver, so this defeats that purpose. Reproducible: Always
Created attachment 73979 [details] View of screens underneath screensaver
I should add that I don't remember this happening before I installed KDE 4.9.0.
I can confirm this behaviour. This should be filed as a security bug. My symptoms match those described by the original reporter. I experience the problem to be somewhat intermittent. This may be hardware related, specifically GPU / X-Windows driver related. I experience this issue on an HP ProBook 6560b with Intel Sandybridge graphics. The CPU with built in GPU is an "Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz" GPU: Intel HD 3000. OS: Kubuntu 12.10 with all recommended and security patches to date. Kernel at 3.5.0.21 XOrg: 1.13.0 (Default with Kubuntu 12.10) Intel module 2.20.9 (Also stock from Kubuntu / updates) $ lspci 00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09) 00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) 00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04) 00:19.0 Ethernet controller: Intel Corporation 82579V Gigabit Network Connection (rev 04) 00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 04) 00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 04) 00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b4) 00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b4) 00:1c.2 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 3 (rev b4) 00:1c.3 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 4 (rev b4) 00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 04) 00:1f.0 ISA bridge: Intel Corporation HM65 Express Chipset Family LPC Controller (rev 04) 00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset Family 6 port SATA AHCI Controller (rev 04) 23:00.0 FireWire (IEEE 1394): JMicron Technology Corp. IEEE 1394 Host Controller (rev 30) 23:00.1 System peripheral: JMicron Technology Corp. SD/MMC Host Controller (rev 30) 23:00.2 SD Host controller: JMicron Technology Corp. Standard SD Host Controller (rev 30) 24:00.0 Network controller: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01) I can provide additional details to help resolve this issue. I have just a few minutes ado gotten a load more updates, including kernel, glib and libc so will monitor to see if anything has improved.
I used to believe there was a problem with the lock screen, but choosing another screen saver than "blank" will remove this security issue. Anyway I confirm this bug with nVidia blob too. This does not seem (too) tied to hardware then... What I see on screen before entering the password is not necessarily what was on screen just before locking, but more likely content from another window. Actually as far as I can remember, it was always Google Chrome's window, like in the screenshot from Leon Maurer. Is it because of the way that browser uses the framebuffer? Maybe related or not: I am sure I saw similar occurrences (usually with added screen corruption) on my previous laptop which was running on some older version of KDE. That laptop had an AMD discrete graphics chip with AMD/Catalyst blob.
*** This bug has been marked as a duplicate of bug 291078 ***