It has permission to trust the input the user enters into it, because that is its job. 20 years ago nobody assumed variable environments were an issue, but this should have been fixed years ago.
I am also pissed that they patched the parser, the feature is still in there when nobody uses it and it has already proven to be a security vuln once.
There are many other ways Bash could do that, though, which would make it much harder for further exploits. Such as opening a pipe and writing them to the sub-process that way so it goes "out of band" from the regular environment variables. Or if it has to be in environment variables: Accept a special argument in the argument list that is a key it uses to sign the variables. It does not need to remain secret - just make sure that just inheriting environment variables with potential attempted exploits is insufficient for anything to get executed.
And/or change the way these definitions are handled - I get that it's tantalizingly simple to just pass this through their usual parser since then you get the function definition parsing for free, but at the very least this parsing of the environment variables shouldn't go through a code path that even potentially executes anything.
