Sure, for example a Rust program is allowed to open, read and write files. On Linux one of the files it's allowed to open /proc/self/mem points directly into its own heap, another is a list of what's in that heap and where - it can use these to scrawl on the heap and cause havoc.
That's the price of being a General Purpose programming language. We don't know if you might want to scribble on your own heap, or delete all the files labelled "Important, DO NOT DELETE" or mail a copy of the password database to a throwaway account, and so you can do all those things. Those Linux files pointing into process address space aren't a mistake, I wrote code that needs them (and then I ported it to safe Rust months ago) but with great power comes great box office potential or something like that.
Now you might say, "I'm sure I won't get something so obvious wrong", but the trouble is that's what the people who wrote this GitHub code apparently thought too. Hence I say we should use specialised languages with a deliberately narrower scope where this category of mistake is impossible.
WUFFS as it stands would be pretty exhausting to write a Markdown parser in because WUFFS doesn't believe in strings, at all. But it's already a better fit for this problem than C++ because the worst case scenario can't happen.
