They are talking about this issue
https://github.com/slime/slime/issues/286
If it has being left unaddressed because no one thinks it is enough of a problem. That is how free software works
https://github.com/slime/slime/issues/286
If it has being left unaddressed because no one thinks it is enough of a problem. That is how free software works
Tl;dr: web sites can send requests to localhost TCP sockets despite origin restrictions using a trick called DNS rebinding.