I wonder how many other unreported silently-patched vulnerabilities are out there?
You seem to be inferring that it is a bad thing to silently patch bugs which may have security implications. The OpenBSD team makes a habit of auditing software for flaws and fixing them without waiting to find out whether they create actual security vulnerabilities. They consider this to be a GOOD thing. I think that people who use software also consider it to be good for software flaws to be fixed as quickly as possible. Inevitably, this means that if the DEVELOPERS discover a flaw, they will fix it before they tell anyone about it. The reason that security researchers publish bulletins about security flaws is because they are unable to fix them either due to lack of skill, or more commonly, they just don't have permission to commit changes to the source code. Network operators are users of software and not developers, therefore most network operators are happy when flaws are fixed early and often. --Michael Dillon