APIs are the foundation of modern software, and REST APIs are everywhere, from mobile apps and e-commerce websites to fintech and healthcare tools. But high connectivity also brings high risks. That’s why securing REST APIs isn’t just about protecting features, it’s about securing sensitive data and keeping your systems safe from evolving cyberattacks.

In this blog post, we will cover: What REST API security is and why it is important, common security use-cases, and most importantly, how these imperative best practices can protect your valuable data and systems so that your REST API works just the way you want it to.

What is REST API Security?

REST API security refers to the measures, protocols, and techniques to secure RESTful APIs against unauthorised access or data breaches, misuse, and vulnerability attack vectors. Representational State Transfer, abbreviated as REST, is an architectural style commonly used in networked applications. REST APIs are designed to enable systems to use HTTP and are often used in web applications, mobile apps, and third-party services.

REST APIs usually hold sensitive data, user credentials, financial data, and health records, making them open to attacks. As an application security engineer, you should know that REST API security isn’t only about authentication and authorisation. It’s all about preserving the confidentiality, integrity, and availability of the data and services exposed by your APIs. Some common ways to secure your REST API are to use service authentication, data validation, rate limits, and monitoring.

Importance of REST API Security

Here's why you need REST API security at the top of your list:

1. Prevent Data Breaches

APIs frequently manage highly sensitive data, including user credentials, financial information, or personal identity information. One small vulnerability can lead to a huge data breach that leaks sensitive data, damaging your organisation’s reputation.

2. Protect Sensitive Information

RESTful APIs serve as a common attack surface for those who are looking to steal valuable data. Good access controls and strong encryption are necessary to keep data from prying eyes and being misused.

3. Block Unauthorised Access

Weak APIs are exploited for unauthorised access to systems and databases inside the client infrastructure. This may cause service interruption, data loss, business dislocation, etc. Robust authentication and access control are fundamental to prevent this.

4. Maintain Reputation and User Confidence

In this digital-first era, trust is the foundation of everything. One API security issue can not only cost you millions of dollars but also ruin your company's reputation forever. It takes a long time to earn back users’ trust once it has been lost in a breach, and many companies are never able to do so.

5. Avoid Compliance Violations

Laws and regulations, such as GDPR, HIPAA, and PCI DSS, may require organisations to secure sensitive data. In an API-centric world, REST APIs are typically the blood vessels of an organisation’s data, and leaving them insecure can lead to serious legal repercussions and compliance violations.

Neglecting REST API security vulnerabilities can result in data breaches, downtime, and financial damage. As an Application security engineer, you should consider REST API security as your foremost priority.

REST API Security Examples

Let’s take a look at some actual, real-life REST API security incidents that demonstrate apparent risks and the importance of a proactive approach in protecting the services.

Example 1: The Broken Authentication

A US fintech startup exposed bank account records of customers over an API endpoint without proper authentication. This REST API flaw was used by attackers to guess account numbers and retrieve sensitive information, exploiting this security vulnerability in a REST API. The breach resulted in regulatory attention and lost customer trust.

Example 2: Overexposure of Data

A popular social media API sent more user information than needed in responses. This REST API security vulnerability was leveraged by attackers to steal email addresses and phone numbers, leading to a targeted phishing campaign.

Example 3: Rate Limiting Failure

A retail e-commerce API failed to carry out rate limiting. The intruders used a brute-force attack, testing thousands of password combinations in a minute. With no proper secure REST API, the cybercriminals in this case could simply go ahead and access users’ accounts without their permission.

Example 4: Injection Attacks

A user input to a healthcare provider API was accepted without validation. The source of the breach was SQL injection; attackers produced malicious SQL queries, and they exploited the database vulnerabilities, providing themselves access to the confidential patient data. The possibility of this REST API security risk could be mitigated with the use of input validation and introducing parameterised queries.

Example 5: Real-Life API Security Vulnerability

A leading US telecommunications company was breached in 2024 after attackers utilised an undocumented API endpoint. The hackers breached millions of customer records, prompting a $10m regulatory fine.

REST API Security Best Practices

1. Use Strong Authentication and Authorisation

Leverage industry-standard protocols such as OAuth 2.0 or JWT for secure authentication. Always authenticate on every API endpoint, and do not trust that an API key is enough. Implement role-based access control (RBAC) to limit user entitlements. Follow the least privilege principle and never keep API secrets in insecure locations.

2. Validate Everything and Filter Input

Never trust the user; validate all incoming user input on the server side. Ensure strict formatting, type, and length of input. Sanitise your input to avoid injection attacks like SQL injection and XSS. Use parameterised queries and encode properly when possible.

3. Use Rate Limiting and Throttling

Secure your APIs from abuse, brute-force and DOS attacks by setting a rate limit. Set thresholds for requests to manage traffic. It lessens the load on servers and helps to protect against automated attacks. Block IPS that are found to be suspicious.

4. Use HTTPS Everywhere

Always use HTTPS (TLS/SSL) to protect data in transit. Sensitive data should never travel over unencrypted HTTP. Through HTTPS, the communications between client and server devices are secured, and man-in-the-middle attacks do not occur. Redirect all HTTP requests to the same URL but using HTTPS.

5. Enable Logging and Monitoring

Keep a close eye on API traffic for any irregular activities or threats. Log all API requests and responses for traceability and forensics. Leverage real-time alerting agents to monitor for anomalies. Platforms such as Akto can automate the detection and reporting of threats.

For more in-depth info, visit our blog: 10 API Security Best Practices.

REST API Security Methods

As an application security professional, you should follow a layered approach with numerous REST API security best practices:

• Authentication: Validate the identity of users with OAuth, JWT, or mutual TLS.

• Authorisation: Implement role-based access control (RBAC).

• Input Validation: Filter and validate all input data.

• Rate Limiting: Prevent abuse by defining request limits.

• Encryption: Encrypt all information in transit using HTTPS/TLS.

• Logging: Log and monitor the usage of APIs for abnormal activity.

• Testing: The APIs trust be actively tested for security weaknesses using automated testing tools.

Final Thoughts

As an application security engineer, you are responsible for securing valuable data, sensitive information and business assets. REST API security is not something that you can simply ignore, it’s a cornerstone of modern application development.

Understanding REST API security, implementing REST API security best practices, and reducing your security risk is imperative to protecting your system against breaches, ensuring compliance, and maintaining the trust of your users. Don’t wait for a breach before acting. Put some solid security in place now.

Akto helps organisations find vulnerabilities, apply security standards, and improve API security. It works smoothly with your existing systems and provides continuous protection without disrupting operations.

Schedule a demo today to see how Akto can keep your APIs safe from new threats.