How would you prove that no input exists that could crash a piece of code? The potential search space is enormous. Microsoft can’t prevent drivers from accepting external input, so there’s always a risk that something could trigger an undetected error in the code. Microsoft certainly ought to be fuzz testing drivers it certifies but that will only catch low hanging fruit. Unless they can see the source code, it’s hard to determine for sure that there are no memory safety bugs.
The driver developers are the ones with the source code and should have been using analysis tools to find these kinds of memory safety errors. Or they could have written it in a memory safe language like Rust.
You don’t need to prove that no input can crash the code. “Exhaustive testing is not possible” is one of the core testing principles, ISTQB teaches that. As far as we know, the input was a file filled with zeroes, and not some subtle configuration or instruction. That can definitely be expected, tested, and handled.
As far as we know, the input was a file filled with zeroes
CrowdStrike have said that was not the problem:
This is not related to null bytes contained within Channel File 291 or any other Channel File.
That said, their preliminary incident review doesn’t give us much to go on as to what was wrong with the file.
You’re speculating that it was something easy to test for by a third party. It certainly could have been but I would hope it’s a more subtle bug which, as you say, can’t be exhaustively tested for. Source code analysis definitely would have surfaced this bug so either they didn’t bother looking or didn’t bother fixing it.
