In today’s connected world, APIs are the backbone of modern software architecture. They enable efficient and flexible communication between diverse systems and are widely used in sensitive areas such as finance and healthcare.

The adoption of REST APIs is growing rapidly, driven by the increasing use of microservices and cloud services, with the number of API calls now growing twice as fast as traditional HTML data traffic.

However, the widespread adoption of REST APIs raises a critical question: How secure are these interfaces, and what challenges do organisations face in their implementation and usage?

What Are REST APIs?

REST, short for "Representational State Transfer," was introduced in 2000 by Roy Fielding and has since become a standard for web services. This architectural style is based on the core principles of the World Wide Web, using standardised HTTP methods such as GET, POST, PUT, and DELETE to interact with resources.

A fundamental principle of REST is statelessness: Each server request must contain all the necessary information to be understood and processed, without relying on server-side stored context. This resource-oriented and stateless approach makes REST APIs particularly flexible, scalable, and easy to implement.

REST APIs are renowned for their simplicity and elegance, as illustrated by a typical API call like "GET /accounts/123abc". This simplicity has contributed to their widespread adoption across nearly all areas of software development. However, they also present specific challenges, especially in terms of security.

Security Challenges

The popularity and versatility of REST APIs bring significant security challenges. Developers face a fundamental dilemma: In order to capitalize on their benefits, REST APIs should be easy to use and integrate, but they must also be robustly protected against misuse and attacks.

An inadequately secured REST API can be exploited without deep technical knowledge, posing a critical risk, especially in domains where sensitive data is handled. A successful attack on an API can lead to data breaches, financial losses, and severe reputational damage for organisations.

To mitigate these risks, authentication should be carried out using standard methods such as OAuth, JWT (JSON Web Token), or HTTP Basic (username, password). Moreover, communication channels must always be encrypted with HTTPS.

To ensure the security of REST APIs, it is vital to integrate security considerations into the development process from the outset. Concepts like Security by Design help identify and prevent vulnerabilities early.

OWASP API Security Top 10

To raise awareness among developers and organisations about the specific security risks of APIs, the Open Worldwide Application Security Project (OWASP) Foundation regularly publishes the API Security Top 10. This list of the most common and critical API security risks serves as an essential guide for the development and operation of secure APIs. The current Top 10 (2023) include:

1. Broken Object Level Authorisation (BOLA): APIs often expose endpoints for object IDs, increasing the risk of access control issues. Each data source access must be carefully validated.
2. Broken Authentication: Flaws in authentication mechanisms allow attackers to compromise tokens or impersonate other users.
3. Broken Object Property Level Authorisation: Insufficient checks at the object level can lead to unauthorised data exposure or manipulation.
4. Unrestricted Resource Consumption: APIs without resource limits are vulnerable to Denial-of-Service attacks and may incur high operational costs.
5. Broken Function Level Authorisation: Complex authorisation policies often introduce vulnerabilities, enabling attackers to access resources or administrative functions of other users.

Alarming Study Results

The study Scorched Earth: Hacking Bank APIs (2021, Alissa Knight) revealed shocking security flaws in bank APIs. The findings were alarming:

• 54 out of 55 tested mobile banking apps contained hardcoded API keys and tokens, including usernames and passwords for third-party services.
• All 55 tested apps were vulnerable to Man-in-the-Middle attacks.
• 100% of tested APIs had Object Level Authorisation (BOLA) vulnerabilities.
• All APIs were prone to authentication issues.
• In one particularly concerning case, it was found that a bank had outsourced code development, and the developer had reused the same vulnerable code for hundreds of other banks.

These findings underscore the urgent need for a comprehensive and consistent approach to API security.

Best Practices for API Security

Given these challenges and risks, it is essential to follow best practices for API security. Key practices include:

1. Robust Authentication and Authorisation:
   • Implement strong authentication mechanisms, preferably using standards like OAuth2 or OpenID Connect
   • Apply granular access controls at the object and function levels
   • Use short-lived tokens and implement secure token management
2. Input Validation and Output Filtering:
   • Validate all inputs rigorously to prevent injection attacks
   • Filter API responses to return only necessary data, avoiding excessive data exposure
3. Rate Limiting and Quotas:
   • Implement rate limits and quotas per API key to prevent DDoS attacks and misuse
   • Monitor unusual usage patterns and respond accordingly
4. Encryption and Secure Communication:
   • Use HTTPS for all API endpoints
   • Implement additional application-level encryption for particularly sensitive data
5. Continuous Monitoring and Logging:
   • Monitor API traffic in real time
   • Maintain comprehensive logs for all API activities
   • Deploy anomaly detection systems to identify unusual patterns or potential attacks early
6. Security-Oriented Development (Security by Design and DevSecOps):
   • Establish security-focused development processes to ensure the implementation of secure authentication mechanisms as described above
   • Security by Design ensures that security considerations are prioritised at every project phase, from conception to rollout
   • DevSecOps facilitates continuous review and automation of security tests throughout the development lifecycle

Conclusion and Outlook

The security of REST APIs is critical in today’s connected world. Given the severe consequences of security breaches, particularly in sensitive sectors like finance, it is vital for organisations and developers to prioritise API security.

The future of API security lies in integrating security considerations into the entire development and operational process. Concepts like Security by Design and DevSecOps are gaining prominence, ensuring that security aspects are incorporated from the outset rather than as an afterthought.

Technologies such as API gateways and specialised API security solutions provide additional layers of protection. These solutions enable centralised management of authentication, authorisation, and monitoring across multiple APIs. Artificial intelligence and machine learning are increasingly being used to detect anomalies and respond to new threats.

The challenge is to strike a balance between usability and security. In order to maximise their benefits, REST APIs must remain easy to use while being robustly protected against potential attacks. With the right approach, continuous vigilance, and the use of modern security technologies, organisations can deliver secure and effective REST APIs that form the backbone of modern, connected applications and maintain user trust.

In an increasingly data-driven world, securing interfaces is more than just a technical necessity—it becomes a strategic priority for any forward-thinking company.

Our Commitment to API Security

The question is: What would our software be without the trust of our clients in its security?

Our Security Circle understands the critical importance of security in modern software development. It is deeply engaged in the latest developments and best practices in IT security, particularly API security. This primarily includes the establishment of DevSecOps in our projects and the regular execution of internal and external penetration tests on our implementations. Through company-wide security standards, we underscore our commitment to the highest security demands in all our products and services.

This proactive approach to IT security not only strengthens our organisation but also benefits our clients by delivering solutions they can always rely on for security and reliability.