Application programming interfaces (APIs) are the backbone of modern web development, enabling communication between online applications. Not surprisingly, API backends have quickly become the prime target of cyberattacks. Protecting against these threats through robust API security best practices is vital to safeguard your backend applications.
In this article, you will dig into the importance of API threat protection and explore some key techniques for securing your backends.
Let’s dive in!
What Is API Security?
API security is the process of protecting APIs against common web attacks, such as data breaches, unauthorized access, and code injection. It focuses on all the practices, strategies, and measures implemented to shield API endpoints and the data they handle from threats and vulnerabilities.
That concept applies to any backend technology, whether it is Node.js, Spring Boot, or Django, and to any types of endpoints, including RESTful, GraphQL, or others. Check out our guide for more guidance on securing Node.js applications in production.
As the great majority of modern web applications rely on APIs, ensuring API security has become a fundamental aspect of the web development process.
Why API Security Is So Important
API security is essential because the web is inherently insecure. As technology evolves, so do the strategies and approaches to exploit it. Considering how advanced malicious bots have become, the number of threats to backend servers has increased significantly in recent years. According to a report from Imperva, nearly one-third of all Internet traffic comes from bad bots. That is alarming!
Common attacks like SQL injection, denial of service, and man-in-the-middle pose serious risks to your API endpoints. If successful, these attacks can result in severe consequences, including:
- Data leaks: User data and privacy breaches that can lead to legal and regulatory penalties for failing to protect sensitive information. For instance, severe GDPR violations can lead to fines of up to 4% of your global revenue.
- Reduced service availability: Disruptions and downtime can lead to financial losses, user dissatisfaction, and legal issues in case of SLA breaches.
- Loss of reputation: Security breaches tarnish your online reputation, triggering negative opinions in the community.
As you can tell, securing a backend is not merely a precautionary measure. Neglecting security can have tangible, detrimental effects on the future of your application and business.
Top 15 API Security Best Practices
Now that you know what API protection is and why it is critical, protect against attacks by applying the API security best practices outlined below
1. Encrypt Communication via HTTPS
By making sure that your backend is accessible only via HTTPS, you can enhance the confidentiality of data exchanged between clients and your server. This is because HTTPS uses the TLS protocol to create encrypted communication channels, protecting sensitive information like session tokens, passwords, and PII data from eavesdropping and tampering.
Additionally, use Secure cookies as part of this HTTPS-only policy. These special HTTP cookies are sent back to the server by the browser only during HTTPS requests, adding an extra layer of security by ensuring they are transmitted exclusively over encrypted connections.
Investing the time to obtain a legitimate SSL/TLS certificate is also important for enhancing the credibility of your backend. While free options like Let’s Encrypt are available, acquiring a certificate from a trusted CA (Certificate Authority) offers additional validation to users.
2. Authenticate Your Endpoints
Authenticating the endpoints in your backend is essential to ensure that only trusted users can access them. Popular API authentication methods include:
- JWT: JSON Web Tokens provide stateless token-based authentication, allowing secure information exchange between parties.
- Basic auth: Using a Base64-encoded username and password in the
Authorizationheader for authenticating server-to-server communication. - API keys: Strings used as unique identifiers to authenticate requests. This technique is commonly adopted in online services providing public endpoints. Effective strategies for API key management involve regularly rotating keys, implementing usage quotas, and monitoring key activity to detect suspicious behavior. Users should also be educated to set API keys only in environment variables and avoid publicly exposing them.
- Client SSL certificates: A process where the client and server validate each other’s identities by exchanging SSL certificates. If the validation is successful, they proceed to establish a secure connection. This mutual authentication approach is commonly used in enterprise environments where high security is required for client interactions.
As part of your authentication policies, you also want to enforce strong authentication policies. This means inviting users to set strong passwords and/or rely on MFA (Multi-Factor Authentication) and SSO (Single Sign-On).
3. Hide Your API Backends Behind a Gateway
Your microservice architecture likely consists of several API endpoints spread across different servers. To protect them all consistently, you should place them behind an API gateway.
API gateways centralize incoming traffic, routing client requests to the correct endpoint on the appropriate server. This means exposing your endpoints only through the API gateway, where you can centralize security measures.
This approach is especially important considering that API security best practices continuously evolve. So, threat protection measures require a lot of changes over time. By centralizing security in an API gateway, maintenance becomes easier and you do not have to keep updating single endpoints.
Also, do not forget that the most secure API backend is one that is not even exposed to the public Internet but is only accessible through a private network. Implementing this involves placing your APIs behind a bastion host or a VPN, giving access only to authorized users who can tunnel into the private network.
4. Enforce Fine-Grained Access Control Strategies
Fine-grained access control (FGAC) is an authorization strategy to allow or deny access to data and resources based on multiple aspects. In particular, it involves granting specific permissions to users based on operations they need to perform on selected resources.
FGAC follows the principle of least privilege, making sure that each user has the minimum required permissions to do what they need to do. This reduces the risk of unauthorized operations and data breaches.
Popular fine-grained access control strategies are:
- RBAC (Role-Based Access Control): Assigning permissions to users based on roles (e.g., admins, editors, visitors, etc.)
- ABAC (Attribute-Based Access Control): Granting access based on user attributes and context (e.g., device, time, location, etc.).
5. Implement API Rate Limiting
API rate limiting is a protection technique that restricts the number of requests a user can make within a specific timeframe. This involves setting constraints on incoming requests to mitigate threats such as DDoS attacks, brute force attempts, and scraping bots.
Two common techniques to implement rate limiting are:
- Block requests: Automatically block any requests that exceed the defined rate limits, returning a
429 Too Many Requestserror. - Delay requests: Introduce a delay before responding to requests that exceed the limits, slowing down the requester.
By limiting the request rate, you can avoid server overloads and ensure fair usage to all users.
6. Limit the Size of Incoming Requests
Most backend servers, frameworks, and libraries have a default request body size limit set to a few megabytes. This can become an issue during request flooding attacks. The problem is that parsing incoming requests takes time and resources, which increases as the request body becomes larger.
To prevent your server from being overwhelmed by large requests, set a size limit for incoming requests. This setting can typically be configured at both the server level (e.g., using the LimitRequestBody directive in Apache) and the application level (e.g., by limiting the size of the incoming request body).
7. Use Standard Error Messages
Each HTTP error code is associated with a standard name, such as “Not Found” for 404. Since these names are concise and not very descriptive, you may be tempted to include longer, more detailed messages in your error responses. Longer messages will help the client better handle the error, but they may also reveal useful information to malicious users.
As a rule of thumb, avoid detailed error responses including stack traces or technical reasons behind errors. This information does not add real value to the client and will only make it easier for attackers to exploit vulnerabilities in your backend. For enforcing API security, opt instead for generic and standardized error messages.
8. Remove the Default Framework Headers
Popular backend technologies often set default HTTP headers in their responses. For example, Express.js and others automatically set the X-Powered-By header with the framework’s name and sometimes even its version.
These default headers expose the underlying technology stack, helping attackers target known vulnerabilities. As a fundamental API threat protection measure, remove these headers to reduce your backend’s attack surface and reduce potential risks.
9. Validate and Sanitize User Input
Input validation ensures that the data received by endpoints adheres to specific formats and respects expected constraints. This API security best practice reduces errors in the business logic of your backend and mitigates XSS (Cross-Site Scripting) attacks.
Meanwhile, input sanitization focuses on removing potentially harmful characters from input data. That protects against popular code injection attacks like SQL injection.
10. Set the Security HTTP Headers
Security HTTP headers are a set of HTTP headers designed to add an additional layer of protection against common web vulnerabilities. These headers include Referrer-Policy, Content-Security-Policy, X-Content-Type-Options, and others. You can check whether your backend sets them correctly at the Security Headers site.
For example, defining a CSP policy through the Content-Security-Policy allows you to specify which trusted sources the browser can load resources from. That mitigates XSS attacks and other common threats.
11. Integrate Logging and Application Monitoring
When something goes wrong, you need to understand when, what, why, and how it happened. This is exactly what logging is all about. By tracking your backend activities in log text files, you can reconstruct events in case of errors to address them more easily.
Similarly, application performance monitoring (APM) involves tracking the performance and health of software. Integrate an APM library into your backend, and this will start sending useful data in the background using standard protocols like OpenTelemetry. That data can then be used to get real-time insights and set alerts for unusual behavior, helping immediately identify suspicious activities and security breaches.
12. Regularly Perform Audits, Penetration Tests, and Stress Tests
A code audit for security involves examining server configurations and the codebase of your backend to ensure compliance with security standards. Instead, penetration tests are more proactive and involve simulating real attacks to identify potential entry points for attackers. Finally, stress tests evaluate API performance under high loads, ensuring resilience against denial-of-service attacks and automated bots.
Regularly conducting code audits, penetration tests, and stress tests helps discover weaknesses in your backend and address them before malicious attackers can take advantage of them.
13. Use Security Linters, SCA, and SAST Tools
Security linter plugins, such as eslint-plugin-security, analyze your code for known vulnerabilities and adherence to API security best practices. In detail, they flag potential issues like unsafe regular expressions or dangerous import instructions.
SCA (Software Composition Analysis) tools evaluate the dependencies used in your application for known vulnerabilities. They identify outdated or insecure components and recommend updates or replacements to keep your software stack secure. Tools like Snyk and Black Duck are popular for performing these analyses. In general, you should always keep your third-party libraries up-to-date, relying on such a service to alert you when known security issues emerge.
SAST (Static Application Security Testing) tools perform comprehensive scans of your codebase to identify security flaws in the logic or architecture of your backend. Examples of SAST tools are SonarQube and Lacework.
By integrating such security tools into your development workflow, you can proactively prevent security risks.
14. Use API Firewalls
API firewalls monitor and filter both incoming and outgoing traffic for malicious activity. When it comes to backend protection, all-in-one web application firewall (WAF) solutions like Cloudflare, AWS WAF, and Akamai have become particularly popular.
WAFs provide comprehensive security by blocking known threats, preventing unauthorized access, and mitigating known attacks such as SQL injection and cross-site scripting. In addition, they generally offer features like rate limiting and bot protection to further enhance the security of your APIs.
15. Follow Established Security Standards
API security is a cat-and-mouse game, with new threats emerging daily and constant updates to security systems to protect against them. This is why staying abreast of the latest developments is imperative!
Adhering to trusted sources like OWASP offers invaluable guidance, helping you keep your backend robust and up-to-date in the face of evolving threats. Specifically, the OWASP Top Ten project provides crucial insights into the most prevalent web threats.
Conclusion
In this guide, you learned how to safeguard backend applications through the adoption of API security best practices. As a developer, it is your responsibility to maintain application functionality, safeguard your users, and prevent data breaches. By incorporating these techniques, you can bolster the resilience of your backend against common web attacks, effectively mitigating risks and safeguarding the security of your application.
Originally published at https://semaphoreci.com on September 20, 2024.
