What do you mean by 'existing exploits'? It seems like they are accusing them of writing insecure code on purpose, which is exactly how i'd go about inserting a backdoor if I were going to do it.
That is correct because plausible deniability is very important.
However writing insecure code is also the defacto standard across industry, definitely including in the US.
If we accept this as proof, then Microsoft, Google, Facebook, etc, (all the way down like the turtles, until we hit every one man company) are all government controlled corporations deliberately installing sneaky back doors through security vulnerabilities in code, which cleverly simply look like incompetent programming.
