On macOS High Sierra 10.13.2, when I manually lock the screen (shift+ctrl+power) and later press any key to turn it on, the screen content which was shown at the time I locked the screen is briefly displayed on the screen (something like 1/30 or 1/60 of a second — I can measure it with high speed camera but it doesn't matter much) before it finally displays the login UI.
I've never seen it before High Sierra, but now I can reproduce this 100% of the time. This is really annoying because this might allow a stranger to capture screen contents which were shown immediately before the screen was locked.
I found one workaround which is far from perfect: lock the screen, wake up and press 'esc' to turn off the screen again. Then at the next wake up, nothing is revealed.
If I use cmd+ctrl+Q to lock the session as suggested in comments, it makes the bug less frequent, but doesn't really solve it. In other words it turns a suicide self shot into a Russian Roulette.
- macOS 10.13.3 is affected
- not fixed in macOS 10.13.4.
- not fixed in macOS 10.13.4 with Security Update 2018-001.
- not fixed in macOS 10.13.5.
- I think I saw it again in macOS 10.13.6 too.
Are there any better workarounds? Is it worth reporting to Apple as a security/privacy bug?