[Discuss] web server can't see out but others can see in

[blu at nedharvey.com (Edward Ned Harvey (blu))]

> From: Derek Martin [mailto:invalid at pizzashack.org]
> 
> You can't attack a service that isn't
> there, or can't hear you.

Why do we care about having a firewall at all?  Why don't we just shut off services that aren't necessary?

To offer some protection against situations where you didn't intend for a service to be on.  Or - Sometimes there will be a vulnerability in one service that allows an attacker to create files on your system, while a vulnerability in some other service allows an attacker to execute code of some pre-existing file, etc.  

Same reason we care about selinux and apparmor.  They allow you to define what "normal" behavior of the system is, and allow you to deny "abnormal" behavior of your system.  The whole point is to limit the freedom of an attacker, even if they have identified a vulnerability.