What is API Vulnerabilities?

API vulnerabilities mention to the possible flaws or breaks in an API’s security that might be utilized by a hateful actor. These vulnerabilities can be present in any portion of the API, from the project stage to the deployment phase. They can consequence in severe penalties, such as unauthorized access, data breaches and even system smashes.

In spite of the important part that APIs play in software submissions, they are frequently gone undefended due to absence of security methods, misconfigurations or just unfamiliarity of the possible threats. This absence of defense can deliver an open door for hackers to utilize these vulnerabilities and advance illegal contact to personal information or systems.

Recognizing these API vulnerabilities is the first step toward mitigating the risks they introduce. By understanding the possible threats and applying the suitable security methods, designers can confirm the security and honesty of their APIs.

Top 10 API Security Vulnerabilities (OWASP API Security Top 10)

1.  Broken Object Level Authorization

Broken Object Level Authorization happens when APIs fail to confirm that a user has permission to access a specific object, even though the user is authenticated. APIs often expose object IDs (like user or order IDs) in request paths or parameters.

If the backend does not check whether the user is authorized to access the requested object, attackers can manipulate the ID to access other users’ resources. For instance, a user changing /api/order/123 to /api/order/124 might gain access to another person’s order details. This is a classic example of Insecure Direct Object Reference (IDOR).

APIs must enforce ownership checks at every endpoint to ensure that only the rightful owner of a resource can access or modify it. Without such validation, sensitive data leaks, account takeovers, or unauthorized actions can easily occur.

Characteristics of Broken Object Level Authorization

Characteristic	Description
Risk Level	High
Exploited By	Modifying object IDs in API requests
Common Scenario	Accessing another user’s data (e.g., user profiles, order details)
Root Cause	Missing or weak access controls at the object level
Prevention	Implement strict object ownership checks in every relevant endpoint

2.      Broken Authentication

Broken Authentication vulnerabilities occur when APIs do not securely authenticate users, allowing attackers to compromise accounts or impersonate users. Issues may arise from poorly protected login endpoints, weak session management, token exposure in logs or URLs, or the absence of multifactor authentication.

Attackers exploit this by brute-forcing credentials, replaying stolen tokens, or hijacking active sessions. APIs are especially vulnerable when they do not enforce secure authentication standards. This can lead to account compromise, privilege escalation, and data breaches.

To prevent this, enforce MFA, set strict password policies, securely manage and rotate tokens, and invalidate sessions after logout or inactivity.

Characteristics of Broken Authentication

Characteristic	Description
Risk Level	Critical
Exploited By	Brute force, session hijacking, token reuse
Common Scenario	Logging in as another user or maintaining access after logout
Root Cause	Weak or improperly implemented authentication mechanisms
Prevention	Use MFA, secure token storage, and session timeouts

3. Broken Object Property Level Authorization

Broken Object Property Level Authorization occurs when an API allows users to view or modify sensitive properties within an object they shouldn’t have access to. Unlike object-level authorization, this focuses on object fields or properties, such as a user changing their role from “user” to “admin” via a JSON payload.

If the backend does not validate whether a user is authorized to change certain fields, attackers can escalate privileges, unlock hidden features, or access protected information. Fine-grained access control and server-side property validation are essential to prevent this type of abuse.

Characteristics of Broken Object Property Level Authorization

Characteristic	Description
Risk Level	High
Exploited By	Injecting unauthorized object properties in request payloads
Common Scenario	Changing roles, status flags, or permissions in user profiles
Root Cause	Lack of fine-grained access control over object fields
Prevention	Validate all fields server-side, allow updates only on authorized properties

4  Unrestricted Resource Consumption

Unrestricted Resource Consumption is a denial-of-service (DoS) risk that occurs when APIs allow clients to consume excessive system resources—CPU, memory, storage, or bandwidth—without any limitations. Attackers may abuse APIs by sending large payloads, looping requests, uploading oversized files, or bypassing pagination.

This overwhelms the server, slows down response times, or crashes services, denying access to legitimate users. APIs should always enforce strict limits on request size, response volume, file uploads, and the rate at which requests can be sent.

Characteristics of Unrestricted Resource Consumption

Characteristic	Description
Risk Level	High
Exploited By	Flooding APIs with large or frequent requests
Common Scenario	DoS attacks using high-frequency API calls or file uploads
Root Cause	Lack of throttling, rate limiting, or request size controls
Prevention	Implement quotas, rate limits, and payload restrictions

5. Broken Function Level Authorization

Broken Function Level Authorization arises when APIs expose functionality (like admin features) without checking if the requesting user is allowed to access that function. This is especially problematic in APIs using role-based access control. For example, if an API has an endpoint like /api/delete-user meant only for admins, and there’s no role verification, any logged-in user could potentially delete accounts.

Attackers explore available functions via tools like Postman or API documentation and test them to find unauthorized access. Each endpoint must verify the user’s role before processing requests.

Characteristics of Broken Function Level Authorization

Characteristic	Description
Risk Level	High
Exploited By	Calling privileged API endpoints without permission
Common Scenario	Non-admin user accessing admin functionalities
Root Cause	Missing role checks on function-level endpoints
Prevention	Validate user roles for each function/API route

6. Unrestricted Access to Sensitive Business Flows

Unrestricted Access to Sensitive Business Flows is a vulnerability where critical business functions are exposed via APIs without sufficient access control or abuse protection. These flows can include high-value transactions such as checkout processes, loyalty point redemptions, or password resets. Attackers can use bots or scripts to rapidly exploit these flows for fraud, resource hoarding, or manipulating business logic.

For instance, an attacker might abuse an API to perform 1,000 automated purchases in seconds or rapidly reset user passwords without rate limits. The absence of safeguards such as CAPTCHA, behavior-based detection, or session validation makes APIs a prime target for business logic abuse.

Organizations must protect sensitive workflows with authentication, authorization, throttling, bot detection, and contextual access control to prevent misuse and financial loss.

Characteristics of Unrestricted Access to Sensitive Business Flows

Characteristic	Description
Risk Level	High
Exploited By	Automating abuse of business logic via scripts or bots
Common Scenario	Mass coupon redemption, checkout manipulation, automated password resets
Root Cause	Missing control over business-critical operations
Prevention	Implement bot detection, rate limiting, and behavioural monitoring

7. Server-Side Request Forgery (SSRF)

Server-Side Request Forgery (SSRF) happens when an API allows attackers to force the server to make requests to internal or external resources on their behalf. This is especially dangerous when the API processes URLs provided in user input without proper validation.

Attackers can craft malicious URLs to access internal systems, metadata endpoints (like AWS’s 169.254.169.254), or conduct port scanning within the internal network. APIs accepting URL parameters—such as webhooks, image fetchers, or file downloaders—are common targets.

If the server blindly fetches the resource, attackers can use it to gain unauthorized internal access, expose sensitive information, or pivot deeper into the infrastructure. The best defense is strict input validation, whitelisting domains, and disabling unnecessary URL fetch functionality.

 Characteristics of Server-Side Request Forgery (SSRF)

Characteristic	Description
Risk Level	Critical
Exploited By	Sending malicious URLs to API endpoints that trigger server-side HTTP calls
Common Scenario	Accessing internal services, metadata, or performing port scans
Root Cause	Invalidated input passed to backend HTTP clients
Prevention	URL whitelisting, avoid direct use of user-controlled URLs, network egress filtering

8. Security Misconfiguration

Security Misconfiguration is one of the most widespread API vulnerabilities and occurs when APIs are deployed with insecure settings, open ports, verbose error messages, outdated components, or default credentials.

APIs running in production with debugging enabled or exposing unnecessary endpoints can leak sensitive information or become targets for automated scanners. Poorly configured CORS policies, lack of HTTPS enforcement, and improper error handling also fall into this category, these weaknesses often arise from rushing deployments, lack of testing or inconsistent DevSecOps practices.

A secure-by-default approach should be implemented, including regular configuration reviews, automated testing, minimal privilege principles, and strict security headers.

Characteristics of Security Misconfiguration

Characteristic	Description
Risk Level	Medium to Critical
Exploited By	Scanning for open endpoints, misconfigurations, or default credentials
Common Scenario	Debug info in error messages, CORS misconfig, open admin APIs
Root Cause	Insecure default settings, poor deployment practices
Prevention	Harden configurations, limit privileges, automate security checks

9. Improper Inventory Management

Improper Inventory Management refers to an organization’s failure to keep track of all deployed APIs, including deprecated versions, hidden endpoints, or third-party services. When APIs are exposed publicly without being catalogued or secured, they become attack vectors.

Many organizations deploy new API versions without retiring old ones, leaving them unmonitored and vulnerable. Attackers scan for forgotten endpoints, legacy APIs, or hidden features that may lack modern security controls. Without a full API inventory, security teams cannot protect what they don’t know exists.

To mitigate this, organizations must maintain a comprehensive API inventory, enforce lifecycle management, and routinely scan for undocumented or shadow APIs.

Characteristics of Improper Inventory Management

Characteristic	Description
Risk Level	Medium to High
Exploited By	Discovering and attacking forgotten or outdated API versions
Common Scenario	Accessing legacy endpoints not monitored or protected
Root Cause	Lack of visibility and control over API versions and assets
Prevention	Maintain an API inventory, deprecate old APIs, automate discovery

10. Unsafe Consumption of APIs

Unsafe Consumption of APIs happens when developers blindly trust external or third-party APIs without validating responses or handling errors securely. This includes assumptions that data from another API is always safe, complete, or in the expected format.

If an external API is compromised, misbehaves, or provides malicious content, it can cascade into vulnerabilities within your own system. For example, if your system processes HTML or scripts returned by another API without sanitizing input, you may inadvertently introduce XSS, command injection, or data leakage.

API consumers must enforce data validation, limit trust boundaries, implement error handling, and sanitize all external data.

Characteristics of Unsafe Consumption of APIs

Characteristic	Description
Risk Level	Medium to High
Exploited By	Malicious or malformed data returned from third-party APIs
Common Scenario	XSS or injection attacks via trusted API responses
Root Cause	Overtrusting external APIs, lack of validation or error handling
Prevention	Validate responses, limit accepted formats, sanitize and escape user input

6 Essential Ways to Secure Your API

Here are the simple methods you can stop assailants from utilizing mutual API security vulnerabilities.

1. Input Validation and Sanitization

Input validation and sanitization is the main line of defend alongside API vulnerabilities. This procedure includes confirmed the honesty and legality of information before it is handled by the API. This can stop an extensive variety of spasms, counting remote code execution, cross-site scripting (XSS), and SQL injection. To implement input authentication effectively, start by establishing a well-defined and strict schema for every API endpoint. This schema must require the type, format, and variety of suitable standards for each input. It must also discard any input that does not imitate to this schema.

Afterward authenticating the contribution, you should clean it by eliminating any possibly harmful gratified. This can contain distinctive atmospheres, HTML tags and scripts. This procedure can stop injection spasms, where an assailant effort to inset spiteful code into your request over the API.

2. Strong Authentication and Authorization

Robust verification and approval are vital to confirming that only official users can contact your API. This cans stopover unlawful interaction and data breaches, which are midst the utmost related kinds of API vulnerabilities.

Verification to the procedure of confirming the individuality of a user or a system, this can be attained over numerous approaches, such as biometric data, tokens or passwords. To fortify your verification procedure, you should reflect applying multifactor verification, which needs users to deliver two or more pieces of evidence to confirm their identity.

Approval, on the other hand, denotes to the procedure of decisive what activities a user or a system is permissible to achieve. This can be founded on parts, authorizations, or access control lists. To support your support procedure, you should appliance the standard of smallest privilege, which means giving every user or system the smallest approvals they necessity to achieve their responsibilities.

3. Rate Limiting and Throttling

Rate limiting and throttling are actual methods to defend your API from rejection-of-service (DoS) bouts, brute force bouts, and other methods of misuse. These methods limit the amount of requirements that an operator or a system can make to your API within a definite period.

Rate regulating sets a cap on the amount of requirements, while regulating decelerates down the handling of requirements once the boundary is touched. These events can be applied on a per-user foundation, a per-IP foundation, or a per-endpoint foundation.

Still, it’s significant to raid a balance amongst security and usability when applying rate restrictive and regulating. Setting the restrictions too low can delay the functionality of your request and annoy your users. On the other hand, set the limits too great can vacant your API vulnerable to outbreaks.

4. Implement an API Gateway

An API doorway helps as a single entrance point for all API traffic, if a layer of concept amongst your request and the fundamental facilities. This can abridge the organization of your API, recover its presentation, and improve its security.

The API entry can apply security rules, accomplish input authentication and cleansing, implement rate controlling and regulating, and deliver other security types. It can also display API traffic, identify rare patterns, and reply to possible threats.

5. Using API Vulnerability Scanning Tools

API vulnerability scanning utensils are software utensils intended to mechanically discover security susceptibilities in your API. They can examine your API for mutual vulnerabilities, such as insecure data transmission, weak authentication, cross-site scripting and SQL injection.

These utensils can deliver a complete report of the vulnerabilities they discover, beside with references for remediation. This can protect you a lot of time and work in classifying and protective susceptibilities, particularly in huge and multifaceted APIs.

6. Test your APIs using Dynamic Application Security Testing (DAST) to identify vulnerabilities during runtime.

Optimistic Security is a DAST tool constructed from the milled up to test APIs and web applications. With provision for an extensive variety of API buildings, test your inheritance and modern applications, counting GraphQL, SOAP and REST API.

Explore More: API Penetration Testing

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