"Unpatched systems represent the number one method of system compromise."
This is a common statement and I'm sure many of you can find various reports that claim to corroborate this sentiment.
I'm not going to argue that point. Why am I still aggravated by this statement then? This sentiment reflects static thinking. It ignores activity over time.
For both opportunistic and targeted threats, when exploiting unpatched vulnerabilities no longer works, over time they will escalate to attacks that do work.
I recognize that if you have to start your security program somewhere, addressing vulnerabilities is a good idea. I get that as a Chief Security Officer.
However, the tendency for far too many involved with security, from the CTO or CIO perspective, is to then conclude that "patched = secure."
At best, patching reduces a certain amount of noise because it deflects opportunistic attacks that work against weaker peers. Should patching become more widespread, opportunistic attackers adopt 0-days. We've been seeing that in spades over the last few months, even without widespread adoption of patches.
In the case of targeted attacks, patching drives intruders to try other means of exploitation. I've seen this first hand, with intruders adopting 0-days as a matter of course or trying other attack vectors. Targeted intruders learn not to trip traditional defenses while failing to exploit well-known vulnerabilities.
If someone asks you if "unpatched systems represent the number one method of system compromise," please keep this post in mind. Remember we face an intelligent adversary who, over time, acts to improvise, adapt and overcome.
We must do the same, over time.