Defense in depth

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Description

The principle of defense-in-depth is that redundant security mechanisms increase security. If one mechanism fails, perhaps the other one will still provide the necessary security. For example, it is not a good idea to rely on a firewall to provide security for an internal-use-only application, as firewalls can usually be circumvented by a determined attacker (even if it requires a physical attack or a social engineering attack of some sort).

Implementing a defense-in-depth strategy can add to the complexity of an application, which runs counter to the “simplicity” principle often practiced in security. That is, one could argue that new protection functionality adds additional complexity that might bring new risks with it. The risks need to be weighed. For example, a second mechanism may make no sense when the first mechanism is believed to be 100% effective; therefore, there is not much reason for introducing the additional solution, which may pose new risks. But usually the risks in additional complexity are minimal compared to the risk the protection mechanism seeks to reduce.

Examples

Vulnerable Administrative Interface

A failed authentication control to the Administrative Interface is unlikely to be enable to anonymous attack on the system as a whole if it correctly gates access to production management networks, checks for administrative user authorization, and logs all access.

References

• National Security Agency Defense In Depth Guide
• CLASP Security Principles