Combining the Zero Trust Security Model with Least Privilege Permissions
There are two modern cybersecurity principles that you can leverage as the corner‐ stones of your serverless security strategy: zero trust architecture and the principle of least privilege.
Zero trust architecture
The basic premise of zero trust security is to assume every connection to your system is a threat. Every single interface should then be protected by a layer of authentica‐ tion (who are you?) and authorization (what do you want?). This applies both to public API endpoints, or the perimeter in the traditional castle-and-moat model, and private, internal interfaces, such as Lambda functions or DynamoDB tables. Zero trust controls access to each distinct resource in your application, whereas a castle-and-moat model only controls access to the resources at the perimeter of your application.
Imagine a knight errant galloping up to the castle walls, presenting likely-looking credentials to the guards and persuading them of their honorable intentions before confidently entering the castle across the lowered drawbridge. If these perimeter guards form the extent of the castle’s security, the knight is now free to roam the rooms, dungeons, and jewel store, collecting sensitive information for future raids or stealing valuable assets on the spot. If, however, each door or walkway had addi‐ tional suspicious guards or sophisticated security controls that assumed zero trust by default, the knight would be entirely restricted and might even be deterred from infiltrating this castle at all.
Another scenario to keep in mind is a castle that cuts a single key for every heavy-duty door: should the knight gain access to one copy of this key, they’ll be able to open all the doors, no matter how thick or cumbersome. With zero trust, there’s a unique key for every door. Figure 4-2 shows how the castle-and-moat model compares to a zero trust architecture.
Figure 4-2. Castle-and-moat perimeter security compared to zero trust architecture
There are various applications of zero trust architecture, such as remote computing and enterprise network security. The next section briefly discusses how the zero trust model can be interpreted and applied to serverless applications.