yes custom roms can. And it isnt that google decided not to fix it, they already have. The newest version of android is available and not vulnerable to this flaw. The users who do not have nexus devices (non officially supported google products) are the ones exposed. If you have a custom rom, most likely the rom maker will update you the newer versions of android making this flaw irrelevant. This is why if you go with android, go with nexus. Google cannot always get patches out as the cell manf. won't spend time to update their old models, and it has to go through a long approval process by the carrier. If you want a fully up to date and support for android, go with a nexus device.
I like the fact that android is open source, I hate the fact its on so many devices that the market is saturated with them. Manufacturers need to stop making a zillion phones every few months.