net-misc/fatrat[bittorrent] depends on dev-qt/qtwebkit:4 which is ancient and will never see any security updates.
If there's no upstream fix or port available, I'd suggest removing that USE flag.
fatrat master is Qt5-based: https://github.com/LubosD/fatrat
USE=bittorrent masked in git commit 35e1693bacfd304572a9de90bc58e724684184ac
Old version removed in git commit b8adb09f6e8d4efb5740a1dfefbf58f3bcbba8b9