API Security Checklist: Expert Tips And Practices

APIs power today’s web applications, bridging the critical gap between customers and service delivery. However, the rapid proliferation of APIs has also made them a prime target for attackers. Several studies confirm the risk is real. Akamai’s State of the Internet report highlights a 49% increase in API-related web attacks in 2024.

This blog provides a comprehensive API security checklist, expert tips,  and best practices to safeguard your APIs.

What is API Security? 

APIs, or Application Programming Interfaces, enable different software systems to share data and functionality. Because they often handle sensitive information, APIs are a common target for hackers.

API security ensures that only authorized users or systems can access these connections. Additionally, API endpoints or nodes must be fully secured to prevent cyberattacks.

This raises the question: How can APIs be secured? Effective measures include authentication, encryption, and regular monitoring to ensure data remains safe during transmission.

API Security: Real World Scenarios

Scenario# 1: Weak credentials and hardcoded mechanism 

< Add Code Snippet #1>

Attackers can exploit weak security measures using brute-force and credential-stuffing attacks. Such security risks increase when systems lack secure authentication practices, such as failing to hash passwords or not implementing token-based authentication.

These risks can be mitigated by enforcing user access control, validating permissions, using hashed passwords (e.g., bcrypt) stored in databases, and implementing rate limiting.

Scenario #2: Encryption

Let’s consider the Python code snippet (PyCryptodome) shown below. It demonstrates the risks of storing sensitive data in plaintext (unencrypted form). It highlights how using encryption can safeguard the data-at-rest.

<Add Code Snippet # 2> 

Attack Scenario #3 Input query with malicious code 

Let’s consider the code snippet as shown below for SQL Injection (Python with Flask):

<Add Code Snippet# 3>

It contains a malicious payload. As a result, the query should not execute due to proper input validation (if fixed). To plug this vulnerability, you can use parameterized queries.

The API Security Checklist

Here is a comprehensive checklist to strengthen API security: 

1. Authentication And Authorization

Authentication and authorization are critical components of API security mechanisms. Authentication verifies user identity, while authorization determines user access levels once the user’s identity is confirmed.

You can use the following checklist to enhance authentication and authorization:  

Avoid Basic Authentication

While basic authentication is easy to use, it’s not recommended due to its security weaknesses. Use stronger alternatives, such as API keys, OAuth, or OpenID. To ensure robust API authentication, use a combination of OAuth 2.0 and JWT authentication mechanisms.  Read more about API Authentication methods here.

Additionally, implementing role-based access control (RBAC) strengthens authorization mechanism. It allows users to access only those resources they have been explicitly permitted by the administrator. 

Implement Two-factor or MFA Authentication

Adding a second layer of authentication makes it harder for hackers to infiltrate the system. For example, if a login triggers a one-time verification code on the user’s device, the hacker will need both the password and physical device access to succeed.

Check Login API Access From HTTPS

Always access login APIs using “https://” to enforce encrypted communication and verify server authenticity. This protects sensitive data, such as login credentials and tokens, from eavesdropping and man-in-the-middle attacks.

Enforce Transport Layer Security (TLS)

Web services without TLS are inherently insecure and can expose sensitive data, such as passwords or credit card details. Transport Layer Security (TLS) mechanism helps encrypt data, which travels between the client and server. It prevents unauthorized parties from intercepting or altering it.

Use a Key Management System (KMS)

A robust Key Management System ensures strong encryption for sensitive data. It integrates authentication protocols and provides audit logs for monitoring, reducing the risk of key misuse, unauthorized access, and data breaches.

Use Server-side Validation

Server-side validation ensures that tokens presented by clients are legitimate and have not been tampered with. For example, when a client sends an access token to access a protected resource, the server validates the token against its issuer by verifying its signature and expiration. 

This prevents unauthorized access and ensures that only authenticated users can perform actions based on their permissions.

2. Encryption

Encryption is essential for securing APIs, ensuring that unintended third parties cannot intercept or access sensitive data. Here is the essential encryption checklist: 

Maintain Robust Storage Encryption for Data-at-Rest 

• Confirm that sensitive data stored in databases and files is encrypted. 
• Ensure AES-256 or stronger encryption is applied to data-at-rest. 
• Validate that API tokens, passwords, and sensitive configuration files are encrypted. 
• Check that disk encryption tools like BitLocker or LUKS are enabled for storage devices containing sensitive data.
• Verify that encryption keys are not hardcoded in source code or configuration files. 

Encrypt Data-at-Rest For Network Encryption 

• Ensure TLS 1.2 or higher is enforced for all network communications.
• Verify the validity of SSL/TLS certificate and ensure it’s not expired. 
• Check for weak cipher suites, such as RC4, MD5, and SHA-1, and disable them. 
• Enable HSTS (HTTP Strict Transport Security). 

Secure Key Management

A robust key management system (KMS) ensures that encryption keys are securely stored and managed. Here is a KMS checklist: 

• Validate that encryption keys are stored securely (e.g., AWS KMS, HashiCorp Vault).
• Rotate API keys periodically and securely destroy old keys.
• Use different encryption keys for different environments (dev, test, prod).
• Ensure unauthorized access to key storage is appropriately prevented.
• Verify that keys are restricted using the principle of least privilege access.

Password And Credential Encryption

• Make sure passwords are hashed using bcrypt, Argon2, or PBKDF2.
• Implement salted hashing to prevent rainbow table attacks.
• Ensure API credentials and secrets are not exposed in logs.
• Test for improper storage of authentication tokens, such as cookies without HttpOnly & Secure flags.

3. Input Validation 

Input validation ensures that only trusted and properly structured data enters the system environment. All data from untrusted sources, such as web clients, backend feeds, partners, or vendors—should be appropriately validated, as it may contain malicious content.

While input validation is not the primary defense against attacks like XSS or SQL injection, it can significantly mitigate the risk. Below is a detailed checklist for input validation:

• Define allowed patterns or exact values to ensure only valid data is accepted. 
• Use native validators (e.g., Django, Apache Commons) or schemas (JSON, XML) to enforce correct data types and formats. For instance, ensure integers are parsed correctly and strings match expected patterns.
• Set minimum and maximum lengths for strings and value ranges for numbers or dates. For example, restrict usernames to 3–20 characters or ensure age values are between 0 and 120.
• Normalize Unicode text to a canonical form and allowlist specific character categories. For example, allow apostrophes in names but block other special characters unless explicitly required.

To learn more about Input Validation checklist, read the OWASP Input Validation Cheat Sheet.

4. Rate limiting 

Authentication And Account Management

• Store API keys securely and restrict their scope to prevent API leakage.
• Ensure access tokens have a short lifespan; refresh tokens should be used securely.
• Limit API access based on user roles and attributes.

 API And User Actions Security

• Enforce HTTPS/TLS 1.2+ for all API requests.
• Validate input and output data to prevent SQL Injection, XSS, and SSRF attacks.
• Restrict file types, scan for malware, and use Content Security Policy (CSP).
• Allow only trusted origins to access your API.
• Ensure API endpoints do not accept unrestricted input for object creation or updates.

Security And Abuse Prevention

• Use API scanners or other tools to proactively detect patterns of abuse and bot activities.
• Be especially cautious of common OWASP API threats.
• Use strong encryption standards like AES-256 to encrypt data-at-rest and transit. 

Logging And Monitoring

• Enable detailed API logging to detect unauthorized log authentication attempts, failed requests, and other suspicious activities.
• Use centralized log management to integrate with SIEM tools for threat detection.
• Set up alerts for repeated failed logins or suspicious API calls.
• Always mask API keys, tokens, and PII in logs to avoid leaking sensitive data.

5. Security Headers

Content Security Policy (CSP) Testing

• Test for missing CSP headers to determine if the application is vulnerable to XSS.
• Verify whether CSP allows unsafe directives that can be exploited.
• Check if CSP restricts script execution only to trusted sources (e.g., ‘self’ or approved domains).
• Test for CSP bypass techniques, such as JSONP endpoints or improperly configured wildcards.

X-Content-Type-Options Testing

• Ensure X-Content-Type-Options: nosniff is set to prevent MIME-type sniffing attacks.
• Test whether the browser is allowed to interpret files as different content types (e.g., forcing an image to execute as JavaScript).

 X-Frame-options Testing for Clickjacking Protection

• Check if X-Frame-Options is missing or set to ALLOWALL, making the site vulnerable to clickjacking.
• Test iframe embedding by loading the site in an <iframe> tag on another domain and attempting to interact with it.

Strict Transport Security (HSTS) Testing

• Check if strict transport security is missing. 
• Ensure HSTS is set with max-age=31536000 (one year) and includes Subdomains and preload.

Cross-origin Resource Sharing (CORS) Testing

• Check if Access-Control-Allow-Origin is appropriately set.
• Verify whether the application allows wildcard origins with sensitive authentication cookies.

Secure Cookies Testing

• Ensure cookies have Secure; HttpOnly; SameSite=Strict attributes to prevent XSS and CSRF attacks.
• Validate if session cookies are transmitted over non-secure HTTP connections.

6.  API Gateway

• Ensure data between clients and the API gateway is encrypted. 
• Verify and sanitize user inputs to block malicious data (e.g., SQL injection, XSS) that could exploit vulnerabilities in the API or backend systems.
• Track and log all API requests to detect suspicious activity, troubleshoot issues, and maintain visibility into API usage and performance.
• Secure APIs with unique keys and manage their lifecycle (e.g., renew, revoke).
• Ensure only authorized users or applications can access the API.
• Limit the number of API requests per user or IP to prevent abuse, ensure fair usage, and protect the API from being overloaded or exploited.

Best Practices for Minimizing API Security Risks 

Here are some best practices to strengthen API security:

Enforce Strong Authentication And Authorization Methods

• Use strong authentication methods, such as OAuth 2.0 and OpenID Connect.
• Implement multi-factor authentication (MFA) to further enhance security. 

Always Use HTTPS for Communications

Using HTTPS protocol validates that data transmitted between clients and APIs is encrypted. It safeguards data from interception or tampering during transmission and against man-in-the-middle attacks. 

Regularly Update And Patch APIs

Keeping APIs updated with the latest security patches is vital for addressing known vulnerabilities. 

• Establish a routine audit schedule to monitor updates from API providers. 
• Always apply patches promptly to mitigate the risk of exploitation by attackers.

Conduct Regular Penetration Testing

Regular penetration testing helps identify potential vulnerabilities within APIs before they can be exploited. Engaging third-party security experts to perform these tests can help detect weaknesses. It allows organizations to strengthen their defenses proactively against emerging threats.

Final thoughts 

On a final note, while a detailed checklist helps address many API vulnerabilities, it’s not enough to fully protect against evolving hacker tactics or the complexity of API systems. It is essential to understand that each component of an API can be exploited, making every API user a potential threat.

BugDazz API Scanner tackles API security risks by offering advanced, automated scanning that continuously monitors for vulnerabilities. Get in touch with us for a free demo.