"is potentially an unauthenticated GET request"
Are you saying that if you don't have a web server that allows "get" requests (only posts) then this exploit is not an issue at all?
(Note I'm not claiming this is the "worst bug ever"... there's stiff competition for that claim. But most of the rest of the "worst bug ever"s I can think of are some point that failed, some particular thing you could do for full root access or something. I can't think of anything else with this sheer staggering surface area.)
Unauthenticated GET requests were just an example of something that can invoke this behavior. If you have any network-enabled service that's capable of spawning a shell, you can have attack vectors open.
Possible vectors include things like DHCP clients, SSH, web servers, etc. Lots of things open shells for reasons you wouldn't intuitively expect. It's very likely that there are many creative vectors for exploitation that will be discovered in the coming hours.
You can learn by experience, or you can try to leach the wisdom of others.
I ask because I've seen SSIDs with meaningful characters ()<>;? cause trouble with some network managers. I presumed at the time that this was due to the SSID string being passed as an argument to some script.
I've encountered this on my old Android phone and my old Debian laptop. I encountered it often because a friend of mine used to have an emoticon in the SSID for his home router. (Really annoying! I couldn't connect to anything when his router was in range.)
Note: it could very well have been a different problem. I didn't investigate.
Usually no. This exploit should be vulnerable to any HTTP method. "unathenticed GETs" are the lowest security level of HTTP calls, so if they can be used as an attack vector, you should pay attention.