Security Pros and Perils of Serverless Architecture

Serverless architectures are revolutionizing the way organizations procure and use enterprise technology. This cloud computing model can drive cost-efficiencies, increase agility and enable organizations to focus on the essential aspects of software development. While serverless architecture offers some security advantages, trusting that a cloud provider has security fully covered can be risky.

That’s why it’s critical to understand what serverless architectures mean for cyber security.

What Serverless Means for Security

Many assume that serverless is more secure than traditional architectures. This is partly true. As the name implies, serverless architecture does not require server provisioning. Deep under the hood, however, these REST API functions are still running on a server, which in turn runs on an operating system and uses different layers of code to parse the API requests. As a result, the total attack surface becomes significantly larger.

When exploring whether and to what extent to use serverless architecture, consider the security implications.

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Security: The Pros

The good news is that responsibility for the operating system, web server and other software components and programs shifts from the application owner to the cloud provider, who should apply patch management policies across the different software components and implement hardening policies. Most common vulnerabilities should be addressed via enforcement of such security best practices. However, what would be the answer for a zero-day vulnerability in these software components? Consider Shellshock, which allowed an attacker to gain unauthorized access to a computer system.

Meanwhile, denial-of-service attacks designed to take down a server become a fool’s errand. FaaS servers are only provisioned on demand and then discarded, thereby creating a fast-moving target. Does that mean you no longer need to think about DDoS? Not so fast. While DDoS attacks may not cause a server to go down, they can drive up an organization’s tab due to an onslaught of requests. Additionally, functions’ scale is limited while execution is time limited. Launching a massive DDoS attack may have unpredictable impact.

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Finally, the very nature of FaaS makes it more challenging for attackers to exploit a server and wait until they can access more data or do more damage. There is no persistent local storage that may be accessed by the functions. Counting on storing attack data in the server is more difficult but still possible. With the “ground” beneath them continually shifting—and containers re-generated—there are fewer opportunities to perform deeper attacks.

Security: The Perils

Now, the bad news: serverless computing doesn’t eradicate all traditional security concerns. Code is still being executed and will always be potentially vulnerable. Application-level vulnerabilities can still be exploited whether they are inherent in the FaaS infrastructure or in the developer function code.

Whether delivered as FaaS or just based on a Web infrastructure, REST API functions are even more challenging code than just a standard web application. They introduce security concerns of their own. API vulnerabilities are hard to monitor and do not stand out. Traditional application security assessment tools do not work well with APIs or are simply irrelevant in this case.

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When planning for API security infrastructure, authentication and authorization must be taken into account. Yet these are often not addressed properly in many API security solutions. Beyond that, REST APIs are vulnerable to many attacks and threats against web applications: POSTed JSONs and XMLs injections, insecure direct object references, access violations and abuse of APIs, buffer overflow and XML bombs, scraping and data harvesting, among others.

The Way Forward

Serverless architectures are being adopted at a record pace. As organizations welcome dramatically improved speed, agility and cost-efficiency, they must also think through how they will adapt their security. Consider the following:

• API gateway: Functions are processing REST API calls from client-side applications accessing your code with unpredicted inputs. An API Gateway can enforce JSON and XML validity checks. However, not all API Gateways support schema and structure validation, especially when it has to do with JSON. Each function deployed must be properly secured. Additionally, API Gateways can serve as the authentication tier which is critically important when it comes to REST APIs.
• Function permissions: The function is essentially the execution unit. Restrict functions’ permissions to the minimum required and do not use generic permissions.
• Abstraction through logical tiers: When a function calls another function—each applying its own data manipulation—the attack becomes more challenging.
• Encryption: Data at rest is still accessible. FaaS becomes irrelevant when an attacker gains access to a database. Data needs to be adequately protected and encryption remains one of the recommended approaches regardless of the architecture it is housed in.
• Web application firewall: Enterprise-grade WAFs apply dozens of protection measures on both ingress and egress traffic. Traffic is parsed to detect protocol manipulations, which may result in unexpected function behavior. Client-side inputs are validated and thousands of rules are applied to detect various injections attacks, XSS attacks, remote file inclusion, direct object references and many more.
• IoT botnet protection: To avoid the significant cost implications a DDoS attack may have on a serverless architecture and the data harvesting risks involved with scraping activity, consider behavioral analysis tools and IoT botnet solutions.
• Monitoring function activity and data access: Abnormal function behavior, expected access to data, non-reasonable traffic flow and other abnormal scenarios must be tracked and analyzed.