API security is the practice of keeping APIs safe from attacks, data leaks, and misuse. An application programming interface API lets different software systems talk to each other. Every time you use a mobile app, check a map, or pay online, API calls run behind the scenes. These API endpoints handle sensitive data like login tokens, payment records, and personal details. Without strong API security, hackers can gain access to this data, disrupt services, or take over accounts. In this guide, you will learn how API security works, what the top security risks are, and how to protect APIs with rate limits, auth, and monitoring at every layer. Web applications, mobile apps, cloud services, and web applications all depend on secure API endpoints to keep users and data safe.
What Is an API and Why Does API Security Matter
An application programming interface API is a set of rules that lets one piece of software send requests to another. Web applications use APIs to fetch data, process orders, and connect to third-party tools. For example, when a travel site shows hotel prices, it sends API calls to each hotel’s booking system. The data flows through API endpoints — the URLs where the API listens for requests. Each endpoint handles sensitive information, from user profiles to payment tokens.
API security matters because APIs are now the main way software connects. The average large firm manages over 600 API endpoints, and API traffic makes up more than 70% of all web traffic. This makes APIs a prime target. In fact, 57% of firms had at least one API-related data breach in a two-year span (Traceable, 2025 State of API Security Report). Hackers love APIs because a single flaw can expose millions of records. A weak API endpoint is like an unlocked back door — it gives attackers a direct path to sensitive data and core systems.
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Types of APIs and Their Security Risks
Not all APIs face the same security risks. REST APIs are the most common type in web applications today. They use HTTP methods like GET, POST, PUT, and DELETE to manage data through API endpoints. Their stateless nature means each API call must carry its own auth token — if that token leaks, the attacker can replay it. SOAP APIs use XML and built-in message-level security, but they are heavier and mostly found in legacy systems. GraphQL APIs let clients ask for exactly the data they want, but they also let attackers craft complex queries that can overwhelm the server or expose excess sensitive data.
Each API type has its own set of security risks. REST APIs are prone to broken access controls and missing rate limits. GraphQL APIs face deep-query denial of service DOS attacks and schema introspection leaks. SOAP APIs can suffer from XML injection and oversized payload attacks. No matter the type, every API must enforce auth, validate input, set rate limits, and encrypt data with transport layer security TLS. Understanding your API types helps you pick the right controls for each.
Top API Security Risks and Threats
API security risks fall into clear groups. The Open Web Application Security Project (OWASP) tracks the worst flaws in its OWASP API Security Top 10 list. This list is the main guide for teams that build and guard APIs. Knowing these security risks helps you focus your defenses where they matter most.
Broken Access Controls
Broken access controls are the top risk on the OWASP API list. They occur when an API fails to check if a user has the right to view or change a given resource. An attacker can tweak an object ID in an API call — changing /users/123/orders to /users/456/orders — and gain access to another user’s sensitive data. BOLA (Broken Object Level Authorization) alone makes up about 40% of all API attacks. This flaw is easy to exploit and hard to catch because the API call looks like normal traffic from legitimate users.
Broken Auth and Session Flaws
If an API does not authenticate and authorize each request well, attackers can steal tokens, hijack sessions, or brute-force logins. Weak auth lets hackers pose as legitimate users and gain access to private data. Transport layer security TLS must protect every API call in transit. Without TLS, tokens and passwords travel in plain text, and anyone on the network can grab them. Every API should enforce HTTPS, use short-lived tokens, and reject unsigned or expired JSON Web Tokens.
Injection Attacks — SQL Injections and More
SQL injections remain a real threat to API endpoints. An attacker sends crafted input through an API call that the backend runs as a database command. This can expose, alter, or delete sensitive data in bulk. Beyond SQL injections, APIs can also face command injection, LDAP injection, and server-side request forgery (SSRF). Input validation on every API endpoint is the first line of defense. Never trust data that comes from outside your system — always check it, strip it, and limit it before the backend processes it.
Denial of Service DOS and Rate Limit Gaps
A denial of service DOS attack floods API endpoints with traffic to crash or slow them. A distributed denial of service DDOS attack uses many sources at once for the same goal. Without rate limits, a single client can send millions of API calls per minute. Rate limits cap how many requests a client can make in a given window. They protect APIs from both brute-force attacks and denial of service DOS floods. Setting rate limits per user, per IP, and per API key is a basic but vital step in API security.
APIs without rate limits are sitting targets. In the Dell breach, hackers sent over 5,000 requests per minute for three weeks straight, scraping 49 million records. The API had no rate limits, no alerts, and no blocks. Always set rate limits on every API endpoint.
OWASP API Security Top 10 at a Glance
The OWASP API Security Top 10 (updated in 2023) gives teams a clear list of the worst API security risks. Each item maps to a real attack pattern that hackers use to gain access to sensitive data, disrupt services, or take over accounts. Here is a quick view of all ten.
| # | Risk | What Goes Wrong | Key Fix |
|---|---|---|---|
| API1 | Broken Object Level Auth (BOLA) | No check on who owns the object | Enforce per-object access checks |
| API2 | Broken Auth | Weak login, token theft | Use OAuth 2.0, short-lived tokens |
| API3 | Broken Object Property Auth | Excess data in API responses | Return only needed fields |
| API4 | Unrestricted Resource Use | No rate limits on API calls | Set per-user rate limits |
| API5 | Broken Function Level Auth | Users reach admin functions | Enforce role-based access |
| API6 | Unrestricted Business Flows | Bots abuse business logic | Add anti-automation controls |
| API7 | Server-Side Request Forgery | API fetches malicious URLs | Whitelist allowed destinations |
| API8 | Security Misconfiguration | Debug on, verbose errors, weak TLS | Harden defaults, audit configs |
| API9 | Improper Inventory Management | Shadow or stale API endpoints | Track all APIs, retire old ones |
| API10 | Unsafe Consumption of APIs | Trust in third-party API data | Validate all external input |
The open web application security project updates this list based on real breach data and input from the global security community. Teams that map their defenses to these ten risks cover the bulk of known API attack patterns.
How to Protect APIs — Core Best Practices
Strong API security rests on a few core pillars: auth, encryption, input checks, rate limits, and monitoring. These controls work together to cut security risks and protect APIs from the threats listed above. Each one covers a different part of the API call lifecycle.
Authenticate and Authorize Every API Call
Every API call must prove who is making it and what they are allowed to do. Auth has two parts. First, the API must authenticate and authorize the caller — confirm their identity and check their access rights. Use OAuth 2.0 or OpenID Connect for token-based auth. Issue short-lived tokens and rotate them often. Second, enforce least-privilege access. Each token should only grant the minimum scope the caller needs. Never give a read-only client write access.
API keys are a common auth method, but they are not enough on their own. An API key proves which app is calling, not which user. Pair API keys with user-level tokens so the API can check both the app and the person behind the request. This dual-layer auth stops stolen keys from giving full access to all data.
Encrypt All Data with Transport Layer Security TLS
Transport layer security TLS encrypts data in transit between the client and the API. Without TLS, API calls travel in plain text — anyone on the network can read tokens, passwords, and sensitive data. Enforce HTTPS on every API endpoint. Reject any request that comes over plain HTTP. Use TLS 1.2 or higher and disable older, weaker versions. Encrypt sensitive data at rest too, so a breach of the database does not expose raw records.
Validate Input to Block SQL Injections
Input validation is the most direct way to stop SQL injections and other injection attacks. Every field in every API call must be checked against a strict set of rules: data type, length, range, and allowed characters. Reject anything that does not match. Use parameterized queries or prepared statements for all database access — never build SQL strings from user input. Also validate output: strip internal IDs, stack traces, and debug data from API responses so attackers cannot map your backend.
Set Rate Limits on Every API Endpoint
Rate limits cap how many API calls a client can make in a given time window. They block brute-force login attempts, credential stuffing, and denial of service DOS floods. Set rate limits per user, per IP, and per API key. Use sliding-window or token-bucket algorithms for smooth enforcement. Return clear 429 Too Many Requests responses so legitimate users know to slow down. Monitor rate limit hits — a sudden spike often signals an attack in progress.
Login endpoints: 5-10 tries per minute per user. Data fetch endpoints: 100-500 calls per minute per token. Batch/export endpoints: 1-5 calls per hour. Adjust based on your traffic patterns, but always start with limits in place — you can loosen them later, but you cannot undo a breach.
API Gateway and Web Application Firewall WAF
An API gateway sits between clients and your backend APIs. It handles auth, rate limits, request routing, and protocol translation in one place. By putting these checks at the gateway, you enforce a single set of rules for all API calls. The gateway also gives you a central log of all API traffic, which makes it easier to spot odd patterns and audit access.
A web application firewall WAF adds another layer. It inspects each API call for known attack patterns — SQL injections, cross-site scripting, and malformed payloads. A WAF can block bad requests before they reach your API endpoints. For the best results, use a WAF that is built for API traffic, not just web pages. Legacy WAFs struggle with JSON payloads, GraphQL queries, and the stateless nature of REST API calls. Modern API-aware WAFs parse API schemas and flag requests that break the contract.
Together, an API gateway and a web application firewall WAF form the outer wall of your API security setup. They catch known threats at the edge so your backend code can focus on business logic. But they are not enough on their own — you still need strong auth, input validation, and monitoring deeper in the stack.
Protect APIs from Shadow and Zombie Endpoints
Shadow APIs are endpoints that exist but are not tracked in your API inventory. They may have been built for a test, a demo, or a quick fix, then forgotten. Zombie APIs are old versions that should have been retired but still respond to API calls. Both create major security risks because they often lack the latest patches, auth rules, and rate limits. If hackers find these stale API endpoints, they can gain access to sensitive data through doors your team forgot to lock.
To protect APIs from shadow and zombie threats, build a full API inventory. Use automated API discovery tools that scan your network, cloud, and code repos for active endpoints. Tag each one with its owner, purpose, and data classification. Retire or block any endpoint that is no longer needed. Make API inventory part of your CI/CD pipeline so new endpoints are logged the moment they are deployed. The OWASP API Top 10 lists improper inventory management as a top risk for a reason — you cannot protect APIs you do not know about.
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API Security in the Age of AI and GenAI
AI tools and GenAI apps have made API security even more complex. These tools rely on dense webs of API calls to fetch data, run models, and return results. Each new AI integration adds more API endpoints to your attack surface. According to the 2025 State of API Security Report, 65% of firms see GenAI as a serious to extreme risk for their APIs. Key concerns include data leaks through API calls to AI models, unauthorized access to sensitive data in training sets, and new attack vectors from model-serving endpoints.
AI also helps the attackers. Bots powered by AI can scan and probe API endpoints at machine speed, testing thousands of input combos per second. They can craft requests that look like normal traffic from legitimate users, making them harder to catch with simple rules. To protect APIs in this new landscape, teams must monitor API traffic patterns in real time, flag odd bursts, and use behavior-based detection that goes beyond static rules. API security is now a race between smart defenses and smart attacks.
65% of firms see GenAI as a serious risk to their APIs. Key threats include: data leaks through API calls to AI models, prompt injection attacks that manipulate API responses, and shadow API endpoints created by AI toolchains that bypass standard security checks. Monitor all AI-related API traffic the same way you monitor user-facing API endpoints — with auth, rate limits, and logging.
How to Build an API Security Program
A strong API security program is not a single tool — it is a process that spans the full API lifecycle. From design to deploy to retire, every stage needs built-in security checks. The timeline below maps out the key phases.
API security is not a one-time task. It is a lifecycle process — design, build, deploy, run, and retire. Every phase needs its own set of checks. Miss one, and you leave a gap that attackers will find.
Third-Party APIs and the Supply Chain Risk
Firms now use an average of 131 third-party APIs (Traceable, 2025). Each one brings its own security risks into your stack. Third-party APIs bring their own security risks. If one has weak auth, missing rate limits, or exposes sensitive data, your app inherits that risk. The OWASP API Top 10 calls this “unsafe consumption of APIs.” Attackers know that firms often trust data from external APIs more than user input. They exploit this by targeting the third-party API first, then using it as a bridge to gain access to your systems.
To protect APIs in your supply chain, vet every third-party API before you integrate it. Check its auth model, TLS setup, rate limits, and data handling. Validate all incoming data from external API calls — never pass it raw to your backend. Monitor third-party API traffic for changes in volume or payload structure that could signal a breach. If a vendor cannot show you their API security posture, that is a red flag. Treat every external API endpoint as an untrusted source, no matter how well-known the vendor.
API Security Testing and Tools
Testing is how you find flaws in web applications and APIs before attackers do. API security testing should run at every stage — in development, in staging, and in production. Automated scanners can check for the OWASP API Top 10 risks, missing auth, open API endpoints, and weak rate limits. Manual penetration tests add depth by probing business logic flaws that tools miss.
Key tools in the API security stack include dynamic application security testing (DAST) scanners that probe live API endpoints, static analysis tools that scan code for flaws before deploy, and API-specific platforms like Salt Security, Traceable, and Wallarm that monitor runtime traffic. A web application firewall WAF and an API gateway round out the toolset by enforcing rules at the edge. The goal is full coverage: test every API endpoint, every auth flow, and every data path. Any gap is a door for attackers to gain access and a source of new security risks.
Monitoring API Security Risks in Real Time
Testing catches flaws before deploy, but monitoring catches attacks in production. Real-time API monitoring tracks every API call across all API endpoints — logging who called, what data was sent, and how the system responded. This data feeds into your SIEM, where it is matched with network and identity signals to spot threats fast. For web applications with high traffic, even a small spike in failed auth attempts or unusual query patterns can signal an attack.
Behavior-based detection goes beyond static rules. Instead of just blocking known bad patterns, it learns what normal API traffic looks like and flags anything that deviates. This is key for catching BOLA attacks, where the API calls look like normal requests from legitimate users but target the wrong objects. It also helps catch low-and-slow attacks — where hackers send a few bad API calls per hour to stay under rate limits. A good monitoring setup covers all security risks: auth failures, injection attempts, bulk data exports, and denial of service DOS patterns. Teams should set up dashboards that show API health, security risks, and error rates for all web applications and services in one view.
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Common API Security Mistakes to Avoid
Even teams with good intent make mistakes that leave APIs exposed. Here are the most frequent errors and how to fix them.
Most of these mistakes are not hard to fix. They persist because teams move fast and skip security reviews. Building API security checks into your CI/CD pipeline catches these errors before they reach production.
API Security for Web Applications and Microservices
Web applications rely on APIs for almost every function — user login, data display, search, payment, and more. Each of these functions runs through one or more API endpoints. In a microservices setup, a single page load may trigger dozens of API calls across different services. This means the attack surface grows with every new microservice you add. Security risks multiply because each service has its own auth logic, its own data store, and its own set of API endpoints.
To protect APIs in web applications and microservices, adopt a zero-trust model. No service should trust another by default. Every API call between services must carry a valid token and be checked against access rules. Use mutual TLS (mTLS) for service-to-service traffic so both sides prove their identity. Set rate limits on internal API endpoints too — a compromised service can be used to flood others with requests. Centralize your API security policy at the gateway level so all web applications and services follow the same rules. This cuts the risk of one team’s shortcut becoming the whole firm’s breach.
API security in microservices also means tracking API endpoints across a fast-moving landscape. Dev teams spin up new services weekly. Without a central API registry, shadow API endpoints appear and grow stale. Use service mesh tools that auto-discover and tag every API endpoint. Feed this data into your security dashboard so your team has full sight of all API calls, all auth flows, and all security risks in real time.
API Security and Data Loss Prevention
APIs are now the main path through which sensitive data moves in and out of systems. That makes API security a key part of any data loss prevention plan. If an API endpoint leaks sensitive information — user records, payment tokens, health data — the breach can affect millions of people. Protecting APIs means classifying the data each endpoint handles, applying access rules based on that classification, and monitoring API calls for bulk data exports that could signal theft.
Encrypt sensitive data both in transit (with transport layer security TLS) and at rest. Mask or tokenize high-value fields like credit card numbers so they never leave your system in raw form. Set up alerts for API calls that return unusually large data sets — this pattern often signals an attacker extracting bulk records. API security and data loss prevention are two sides of the same coin: both aim to keep sensitive data where it belongs. For web applications and cloud services that handle payment or health data, this is not optional — it is a core compliance need.
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API Security Compliance and Governance
API security is not just a tech issue — it is a governance need. Firms that handle payment data must meet PCI DSS rules, which require strong auth, encryption, and logging for all API endpoints that touch card data. Health care firms must comply with HIPAA, which demands strict access controls and audit trails for API calls that carry patient records. Financial firms face SOX and GLBA rules that extend to every API endpoint handling sensitive data.
Good API security governance starts with a clear policy. Define who owns each API, what security risks it carries, and what controls must be in place before it goes live. Build API security reviews into your change management process so no new API endpoint ships without an auth check, rate limits, and input validation. Track compliance status in a central dashboard and run periodic audits against the OWASP API Top 10. Web applications and their APIs should be tested at least quarterly, with results logged for auditors.
Governance also means holding third-party APIs to the same standards. Your contracts should require vendors to maintain transport layer security TLS, enforce rate limits, and notify you of any breach within a set time frame. If a vendor’s API cannot meet your security risks policy, do not integrate it. The security risks of a breach caused by a weak third-party API always outweighs the effort of finding a more secure option.
Frequently Asked Questions About API Security
References
- Traceable, “2025 Global State of API Security Report” — https://www.traceable.ai/2025-state-of-api-security
- Salt Security, “State of API Security Report” — https://salt.security/api-security-trends
- Wallarm, “2025 API ThreatStats Report” — https://www.wallarm.com
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