Defence in Depth

Far to often organisations do all their security work on the few systems that are exposed to the internet. This might be acceptable when you begin the structured and ongoing work with security, but you should try to move on to defence in depth as soon as possible. Defence in depth is where you do not leave security to one layer of an application (or solution), but instead validate the security every step of the way. A common example for this is that even if you have a network firewall you do not disable the firewall in the operating system. This can be transferred to software development as well. In a more complex system each component should get the same security controls. It should not only be the frontend API that validates the input, instead each component should validate the data as untrusted when it receives it from another component. By doing so the resilience of the solution as a whole is greatly improved, where a single issue have limited impact, and might not even be exploitable. ...