There was a discussion here a few years ago (
https://news.ycombinator.com/item?id=2686580) about memory vulnerabilities in C. Some people tried to argue back then that various protections offered by modern OSs and runtimes, such as address space randomization, and the availability of tools like Valgrind for finding memory access bugs, mitigates this. I really recommend re-reading that discussion.
My opinion, then and now, is that C and other languages without memory checks are unsuitable for writing secure code. Plainly unsuitable. They need to be restricted to writing a small core system, preferably small enough that it can be checked using formal (proof-based) methods, and all the rest, including all application logic, should be written using managed code (such as C#, Java, or whatever - I have no preference).
This vulnerability is the result of yet another missing bound check. It wasn't discovered by Valgrind or some such tool, since it is not normally triggered - it needs to be triggered maliciously or by a testing protocol which is smart enough to look for it (a very difficult thing to do, as I explained on the original thread).
The fact is that no programmer is good enough to write code which is free from such vulnerabilities. Programmers are, after all, trained and skilled in following the logic of their program. But in languages without bounds checks, that logic can fall away as the computer starts reading or executing raw memory, which is no longer connected to specific variables or lines of code in your program. All non-bounds-checked languages expose multiple levels of the computer to the program, and you are kidding yourself if you think you can handle this better than the OpenSSL team.
We can't end all bugs in software, but we can plug this seemingly endless source of bugs which has been affecting the Internet since the Morris worm. It has now cost us a two-year window in which 70% of our internet traffic was potentially exposed. It will cost us more before we manage to end it.