Update to BCP-38?

Tue Oct 8 17:53:33 UTC 2019

On Tuesday, 8 October, 2019 11:03, William Herrin <bill at herrin.us> wrote:

>Limiting the server banner so it doesn't tell an adversary the exact OS-
>specific binary you're using has a near-zero cost and forces an adversary
>to expend more effort searching for a vulnerability. It doesn't magically
>protect you from hacking on its own. As you say, your security must not
>be breached just because the adversary figures out what version you're
>running. But viewed as one layer in an overall plan, limiting that
>information enhances your security at negligible cost. That's security
>smart.

I think your analysis is incorrect.  

There are two cases which are relevant:
(1) The attack is non-targetted (that is, it is opportunistic)
(2) The attack is targetted at you specifically.

In the former (1) case, it does not matter whether the "banner" identifies the specific OS binary or not as it is irrelevant.  The script either works or it does not.  Even if the "banner" says "Beyond this point there be monsters" will make absolutely not one whit of difference.

In the latter (2) case, it does not matter whether the "banner" identifies the specific OS binary or not as it is irrelevant.  You have been targetted.  All possible exploits will be attempted until success is achieved or the vat of exploits to try runs dry.

So while the cost of doing the thing may be near-zero, it is not zero.  All those near-zero cost things you do that have no actual advantage can add up to quite a huge total and it will be more advantageous to spend that somewhere where it will, in fact, make a difference.

-- 
The fact that there's a Highway to Hell but only a Stairway to Heaven says a lot about anticipated traffic volume.