If cyberattacks counted, the US would be at war with China and Russia. I bet there will be a treaty eventually, and I have some fears on what secondary restriction it will place on the internet.
A treaty that is unenforceable (ie no one can observe the outcome) is as good as no treaty. You can't really attribute most cyberattacks and if you automatically assume it is country x, then country y in conflict with country x will rush into attacking you.
Oh, they could make it enforceable, but I don't think anyone would really like the resulting version of the internet except bureaucrats who crave power over all things.
You see some politicians mention that all software developers should be licensed, and we see companies requiring signed code to allow it to run on platforms. Licenses for servers happen in some places. Its all little step, but a few more gets you a locked and licensed computing network.