[Development] Which branch to commit patch

[Kurt Pattyn]

Hi,

I have resolved a DoS vulnerability in the Qt WebSockets module (see https://bugreports.qt.io/browse/QTBUG-48123).
Which branch should I commit this patch to: 5.3, 5.4, 5.5, 5.6 or dev?
This issue is present from the very first version (since Qt 5.3).

Cheers,

Kurt