Older versions of Qt actively supported for security patches?
Unsolved
General and Desktop
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Only for 3 more months https://en.wikipedia.org/wiki/Qt_version_history but the branch has not been touched for ~2 years http://code.qt.io/cgit/qt/qt5.git/refs/heads
If you are using that version because of QtWebKit it's even worse as the included version is old and unsupported. You could get WebKit for the recent Qt that is supported (it's a project on github called QtWebKit Revived or something like that) and patched but, if you can, you should switch to QtWebView
