6 Common API Security Risks and How to Protect Your Servers

APIs are the backbone of modern applications, powering data exchange between platforms, devices, and services. But with this reliance comes a growing set of security risks. If left unchecked, vulnerabilities in APIs can expose sensitive data, disrupt services, and put users at risk.

In this post, we’ll walk through six of the most common API security issues and explore practical steps to safeguard your servers.

1. Cross-Origin Resource Sharing (CORS)

CORS is a browser mechanism that controls which domains are allowed to send requests to your server. When configured poorly, it can open the door for unauthorized access.

• The risk: Allowing every domain (*) to access your API means malicious sites can freely interact with it.
• The fix: Set strict rules so only trusted domains can make requests. This keeps harmful websites from embedding or misusing your API.

CORS doesn’t stop every kind of attack, but it’s an essential line of defense in protecting browser-based interactions.

2. Error Disclosure

Detailed error messages are a goldmine for attackers. Exposing internal details such as frameworks, database queries, or stack traces can guide malicious users straight to weak points.

• The risk: Revealing technical details makes it easier for hackers to exploit vulnerabilities.
• The fix: Keep user-facing error messages simple and generic, while logging detailed information privately for developers. This ensures troubleshooting can still happen without leaking sensitive system data.

3. Information Leaks

Sometimes, servers unintentionally reveal too much information through headers or other metadata. For example, a response header might disclose the exact server software and version, which attackers can cross-reference against known vulnerabilities.

• The risk: Giving away system details helps attackers map your infrastructure.
• The fix: Strip unnecessary headers such as Server or X-Powered-By. Use tools or configurations (like helmet in Express.js or server_tokens off in Nginx) to reduce what’s exposed.

4. Insecure Cookies

Cookies often store session data, but if not configured correctly, they can be intercepted or manipulated. Attackers might forge cookies to gain unauthorized access or steal sensitive data.

• The risk: Cookies without proper restrictions can be stolen or altered, leading to account takeovers.
• The fix: Always use Secure and HttpOnly flags, and avoid storing sensitive information directly in cookies. Treat all cookie data as untrusted and validate it on the server side.

5. Path Traversal

Path traversal flaws occur when attackers manipulate input to access files or directories outside of the intended scope. For instance, they may craft requests that retrieve configuration files or sensitive logs.

• The risk: Unauthorized access to private files can expose critical data or even compromise the server.
• The fix: Validate all user input, enforce whitelists of allowed files, and escape characters like ../ or \. Strong server configurations and restricted file system permissions add another layer of protection.

6. Lack of Rate Limiting

Without limits on how many requests can be made in a given timeframe, APIs are vulnerable to abuse. Attackers can launch denial-of-service (DoS) attacks or brute-force login attempts simply by flooding your system with traffic.

• The risk: Overloaded servers, service outages, and higher infrastructure costs.
• The fix: Implement rate limiting through middleware or third-party services. Define thresholds that align with your traffic patterns, and decide whether to block requests or return controlled error responses when limits are exceeded.

Final Thoughts

APIs open the door to innovation, but they also attract threats. By recognizing vulnerabilities like misconfigured CORS, error disclosures, and insecure cookies, you can design defenses that make your systems more resilient.

Security is never a one-time fix—it’s an ongoing process of monitoring, testing, and improving. With a thoughtful, layered approach, you can keep your APIs reliable, secure, and ready to support your users with confidence.