Enterprises use APIs to connect applications and platforms, connecting to the database that stores sensitive user information. A compromised API can quickly lead to attacks on connected applications and, worse, the loss or theft of user data. API security breaches at major companies cost billions annually, with 91% of organizations experiencing an API security incident in the past year. These five essential security tests can help you avoid becoming another statistic.
1. Authentication & Authorization Testing: The First Line of Defense
Strong authentication and authorization mechanisms form the backbone of API security, preventing unauthorized access to sensitive endpoints and data.
Major vulnerabilities arise from weak authentication schemes, improper implementation of role-based access control (RBAC), and flawed token validation.
To properly test authentication and authorization:
- Test JWT validation thoroughly, including token expiration, signature verification, and claims validation
- Verify OAuth flows by checking token exchange, scope validation, and proper refresh mechanisms
- Test RBAC by attempting to access resources with different user roles and permissions
- Ensure API keys are properly validated and cannot be bypassed with header manipulation
- Tools like OWASP ZAP, Burp Suite, and Postman help automate these security tests with predefined security scans and custom test scripts.
2. Input Validation & SQL Injection Testing: Preventing Data Manipulation
SQL injection remains one of the most common attack vectors for APIs, allowing attackers to execute unauthorized database queries or commands.
The root cause typically stems from direct concatenation of user input into SQL queries and inadequate input sanitization.
To test for SQL injection vulnerabilities:
- Send payloads with SQL syntax like ' OR '1'='1, UNION SELECT, and DROP TABLE users;
- Test all input parameters, including query parameters, headers, and request bodies
- Verify handling of special characters, extreme input lengths, and unexpected data types
- Check responses for SQL errors that might reveal database structure
3. Limit Data Sharing
One way of minimizing API vulnerabilities is by minimizing exposure. For a product to work, data is shared between APIs, APIs and applications, and APIs and users. This could be access data like tokens, user data, JSON code, etc.
As the amount of data being shared between nodes increases, the risk exposure also increases. A mechanism like OAuth works well against security threats – it reduces the data being shared between platforms to an authorization key rather than the user’s credentials, so in case of an attack, the attacker does not get any useful information.
Track the data being shared between apps, APIs, and users to identify points of vulnerability and then secure them by limiting the shared data.
4. Always use HTTPS
An HTTP connection does not protect data and can be highjacked to steal information.
An HTTPS connection, on the other hand, encrypts most of the data and helps secure the connection. An HTTPS connection guarantees three things:
- Authenticity – The connection has been made with the real API or application and not an imposter
- Confidentiality – All data (metadata, cookies, and so on) is encrypted and secure
- Integrity – The data being transferred can be trusted and has not been modified or tampered with.
5. Store Passwords Securely with One-Way Password Hashing
Ensuring APIs have a strong strategy for password storage is vital to minimizing security breaches.
APIs that use basic authentication (username and password) have to store this data within a database. If the database is hacked by an external threat or accessed internally by a bad actor, user credentials can be stolen and used to access personal accounts.
One way of protecting credentials is by hashing passwords before committing them to the database.
Hashing uses a hash function (like SHA-1) to convert an input string of any size to a hashed string of a fixed size. For example:
Input data of different characters and lengths are converted to fixed-size hash keys.
Unlike encryption which has a decryption key that can extract the original data from the encrypted output, the output of a hashing function cannot be reversed to obtain the original data.
When a user tries to log in, the API will hash the entered password and match it against the stored hash. The hash will be the same only if the entered password is the same, and this is how users are authenticated.
If the database is compromised, all the attacker gets are hashed strings that cannot be reversed to get the original data.
6. Enforce a Zero-Trust Policy
When it comes on API security Tips, we can exclude the zero-trust policy. It assumes that every user, device, and server is untrusted until proven trustworthy.
The conventional verification model is to trust some connections based on predefined protocols, for example, a connection made from a device within the company network or by a user who has accessed the API before. Any connection from outside this predefined perimeter is asked to authenticate and verify itself before it can access data.
In the zero-trust model, all connections (with absolutely no exceptions) are asked to authenticate before they can access resources. This greatly reduces security risks.
7. Encrypt Data Using TLS
It’s prudent to encrypt all data handled by the API, whether it is Personally Identifiable Information (PII) or connection data being transmitted. Encrypted data cannot be misused, even if attackers somehow steal it. One way of encrypting data in transit is by using TLS with REST/API.
8. Implement Data Logging
Next on our list of API security tips is data logging. Logs are incredibly useful in troubleshooting issues and finding solutions, enabling server and application-level logging.
Define a retention period for these logs, so there is enough historical data to identify breaches much after they have occurred while also ensuring storage space isn’t exceeded.
Logs help with manual inspection and monitoring and give admins a ton of information that can be used to improve API security.
9. Set API Rate-limiting
API limiting, or API rate limiting, is enforcing a limit on clients’ quantity or size of data being requested (or consumed).
The number of connections being made, and the size of requests affects the API’s performance. Allowing unrestricted access can result in excessive connections, which will cause the API server to lag and eventually crash, which happens in the case of a Denial of Service (DoS) attack. In a DoS attack, attackers continuously send large volumes of requests to overload and crash the server, denying service to actual users.
Applying API rate limits helps mitigate the risk of API crashes. Admins can limit the number of requests and transactions per request to maintain balance and optimum performance.
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