Why is QsslSocket working with Qt 5.3 but not Qt 5.7 on Debian Stretch?

Question

I have an app that uses the QWebSocket class but not SSL. It works fine when I execute a version compiled with Qt 5.3 but a Qt 5.7 executable freezes on the following warnin

Answer 1

I had the same problem on a debian stretch server. I fixed it with the help of 7hibaults comment.

Running the following command fixed the problem for me:

sudo apt-get install libssl1.0-dev