OWASP Top 10 API Security Risks and How to Mitigate Them

What Is the OWASP API Security Top 10? 

The OWASP API Security Top 10 is an awareness document for developers and application security practitioners, outlining the most significant security risks to application programming interfaces (APIs) and providing guidelines for mitigating them. 

Developed by the Open Web Application Security Project (OWASP), this list serves as a guideline for enhancing the security of APIs, which are integral to modern web services and applications, and thus have become a prime target for attackers. The OWASP API Security Top 10 aims to educate and encourage the adoption of best practices in API development and maintenance, reducing vulnerabilities and protecting against exploitation.

This document was first released in 2019, updated in 2023, and is planned to be regularly updated in the future to reflect the evolving nature of web security threats. Each item in the top 10 list represents a common or critical issue identified through a combination of industry survey data, expert opinions, and documented incidents. By focusing on these top risks, organizations can prioritize their security efforts, ensuring that they address the most pressing vulnerabilities in their API ecosystems.

See the official OWASP API Security project page.

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Top 10 Risks in OWASP API Top 10

Let’s briefly review the OWASP API top 10 security risks. 

API1:2023: Broken Object Level Authorization

Broken Object Level Authorization (BOLA) vulnerabilities occur when an API fails to properly verify that a user is authorized to access or manipulate specific resources. This can lead to unauthorized access to sensitive data or functionality, allowing attackers to view, modify, or delete data they shouldn't have access to.

Mitigating BOLA requires implementing robust authorization checks consistently across all API endpoints. This includes verifying the user's permissions before performing any action on an object, ensuring that only authorized users can access or modify data. Employing a least privilege approach and regular audits of permission settings can further protect against BOLA vulnerabilities.

API2:2023: Broken Authentication

Broken Authentication vulnerabilities occur when API security mechanisms fail to properly authenticate users, allowing attackers to assume the identity of legitimate users. This can result in unauthorized access to sensitive information and functionality, leading to data breaches and system compromise. These vulnerabilities often arise from inadequate management of authentication tokens, weak password policies, and flaws in multi-factor authentication processes.

To prevent broken authentication, it's crucial to implement strong authentication mechanisms, such as OAuth or OpenID Connect, and enforce strict password policies. Utilizing multi-factor authentication (MFA) adds an additional layer of security, reducing the risk of unauthorized access even if passwords are compromised.

API3:2023: Broken Object Property Level Authorization

Broken Object Property Level Authorization vulnerabilities are similar to BOLA but occur at the property level within objects. Many API endpoints return an object’s properties. The issue arises when an API does not properly check a user's permissions before allowing them to view or modify the properties of an object. This can lead to unauthorized disclosure or alteration of sensitive data contained within an object's properties. In severe cases, it can lead to privilege escalation or account takeover.

Mitigating BOPA involves implementing fine-grained access control that includes property-level authorization checks. This ensures that users can only interact with the properties of an object that they are explicitly authorized to access, protecting sensitive data from unauthorized access or modification.

API4:2023: Unrestricted Resource Consumption

Unrestricted Resource Consumption vulnerabilities can lead to Denial of Service (DoS) attacks, where an attacker exploits an API to consume excessive resources, such as CPU, memory, or bandwidth. This can render the API or the entire application slow or unresponsive, impacting availability for legitimate users. These vulnerabilities often result from allowing uncontrolled input, such as very large request payloads or high-frequency requests.

To protect against unrestricted resource consumption, implementing rate limiting and request throttling is essential. This controls the rate at which users can make API requests, preventing excessive consumption of resources. Additionally, input validation can help ensure that requests do not contain payloads that could lead to resource exhaustion.

API5:2023: Broken Function Level Authorization

Broken Function Level Authorization (BFLA) vulnerabilities occur when an API does not adequately enforce user permissions at the function level. This can allow users to perform actions or access functionality that should be restricted, such as accessing administrative features or performing actions as another user. BFLA vulnerabilities arise from flaws in the way that permissions are checked before a function is executed.

Mitigation of BFLA requires implementing comprehensive authorization checks at the function level, ensuring that a user's permissions are validated before any sensitive function is accessed. Employing the principle of least privilege, where users are granted only the permissions necessary for their role, can also help reduce the risk of BFLA vulnerabilities.

API6:2023: Unrestricted Access to Sensitive Business Flows

Unrestricted Access to Sensitive Business Flows vulnerabilities occur when APIs fail to properly restrict access to workflows that should only be available to certain users or under specific conditions. Attackers can exploit these vulnerabilities to access or manipulate business processes, potentially leading to financial loss, data breaches, or other adverse impacts. These vulnerabilities highlight the importance of securing not just individual API endpoints but the business logic that governs how those endpoints are used.

Mitigating these vulnerabilities involves implementing strict access controls and workflow validations, ensuring that each step of a sensitive business process is protected against unauthorized access. Regularly reviewing and testing business flow implementations can also help identify and address potential vulnerabilities before they can be exploited.

Learn more in our detailed guide to business logic vulnerabilities (Coming soon).

API7:2023: Server Side Request Forgery

Server Side Request Forgery (SSRF) vulnerabilities occur when an attacker can induce the server to make requests to unintended locations or services. This can allow attackers to bypass firewall protections, access internal services, or interact with external systems in unauthorized ways. SSRF vulnerabilities exploit the way an API processes user-supplied URLs or other input used in making requests.

Preventing SSRF requires validating and sanitizing all user-supplied input, especially URLs, and restricting the API's ability to make requests to untrusted sources. Employing network segmentation and firewall rules to limit the scope of internal requests can also reduce the risk of SSRF attacks by limiting the attacker's ability to interact with internal resources.

API8:2023: Security Misconfiguration

Security Misconfiguration vulnerabilities arise from improper configuration of APIs and their supporting infrastructure. This can include misconfigured permissions, unnecessary services running, or exposed sensitive information through error messages or misconfigured headers. Such vulnerabilities provide attackers with easy access to exploit the application, leading to data breaches or unauthorized access.

Mitigating security misconfiguration involves regularly reviewing and auditing API configurations, ensuring that they are secure and align with best practices. Employing automated tools like dynamic application security testing (DAST) tools, which can detect misconfigurations and vulnerabilities in running applications, can also help identify and address issues promptly. Additionally, minimizing the attack surface by disabling unnecessary features and services reduces the risk of exploitation.

API9:2023: Improper Inventory Management

Improper Inventory Management vulnerabilities occur when organizations lack visibility into their API landscape, including outdated or undocumented APIs. This can lead to unmonitored endpoints being exploited by attackers, as these APIs might contain known vulnerabilities or be inadequately secured. Proper API inventory management is crucial for understanding the scope of potential security risks and ensuring that all APIs are accounted for and protected.

Addressing improper inventory management requires implementing processes and tools for dynamically discovering and documenting all active APIs. Automated API discovery tools play a crucial role. Once organizations discover their APIs, they must regularly audit and assess their security and ensure vulnerabilities are remediated. Maintaining an up-to-date inventory also aids in compliance efforts and risk management by providing a comprehensive view of the API ecosystem.

API10:2023: Unsafe Consumption of APIs

Unsafe Consumption of APIs vulnerabilities refer to the risks associated with consuming third-party or external APIs without adequate security measures. This can include failing to validate inputs from external APIs, not enforcing proper authentication, or relying on APIs that are insecure or compromised. Such vulnerabilities can lead to data breaches, unauthorized access, or the propagation of security issues from one application to another.

Mitigating the risks of unsafe API consumption involves thoroughly vetting external APIs before integration, ensuring they meet security standards and are from reputable sources. Implementing input validation and output encoding when consuming APIs can prevent injection attacks or other issues arising from untrusted data. Regularly monitoring and auditing the security of external APIs is also critical to maintaining the security of the consuming application.

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While OWASP recently updated their Top 10 API Security risks list, earlier this year we conducted a research that demonstrates misalignment between these vulnerabilities and real-world scenarios.

Get the full report here.

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Other OWASP Top 10 Projects 

OWASP Web Application Security Top 10

The OWASP Web Application Security Top 10 is a widely recognized document that outlines the ten most critical web application security risks. It serves as a foundational guide for developers, security professionals, and organizations to understand and mitigate common vulnerabilities that web applications face. 

The list includes risks such as injection flaws, broken authentication, and sensitive data exposure, providing practical recommendations for prevention and mitigation. Regularly updated based on evolving threats and industry feedback, the Web Application Security Top 10 emphasizes a proactive approach to web security, encouraging the integration of security practices throughout the software development lifecycle.

OWASP Mobile Top 10

The OWASP Mobile Top 10 addresses the most pressing security concerns for mobile applications. It covers vulnerabilities such as improper platform usage, insecure data storage, and insufficient cryptography, offering guidance for developers and security teams on securing mobile apps against these risks. 

The Mobile Top 10 aims to raise awareness of mobile security issues and promote the adoption of secure coding practices, helping to protect sensitive information on mobile devices and prevent unauthorized access or data loss.

OWASP Cloud-Native Application Security Top 10

The OWASP Cloud-Native Application Security Top 10 focuses on the security challenges specific to cloud-native applications, which leverage microservices, containerization, and orchestration tools. This project identifies key risks such as misconfiguration, insecure APIs, and inadequate monitoring and logging, providing insights into securing applications in a cloud-native environment. 

By addressing these vulnerabilities, organizations can ensure their cloud-native applications are resilient against attacks, safeguarding data and maintaining the integrity and availability of services in the cloud.

Mitigating OWASP API Top 10 Risks: The OWASP REST Security Cheat Sheet

To mitigate OWASP API Top 10 risks, organizations are encouraged to implement the following security measures:

• Use HTTPS: Secure your REST services by only offering HTTPS endpoints to protect data and credentials in transit, ensure data integrity, and authenticate the service.
• Implement Access Controls: Apply access control on each API endpoint to manage access based on user authentication, authorization logic, and session management. Centralize user authentication through an Identity Provider (IdP), which issues access tokens.
• Use JWTs: Adopt JSON Web Tokens (JWT) for security tokens, ensuring they are protected with a signature or MAC. JWTs carry a set of claims for access control decisions, and their integrity must be validated.
• Use API Keys: To mitigate the risk of excessive use or attack on public REST services without access control, use API keys as part of the request, ensuring they are managed securely.
• Restrict the Use of HTTP Methods: Limit allowed HTTP methods (e.g., GET, POST, PUT) and reject requests not adhering to these methods to protect against unauthorized actions.
• Validate Inputs: Ensure input validation for all incoming data to protect against malicious input, using type constraints, regexps, and validation libraries.
• Protect Management Endpoints: Keep management endpoints inaccessible via the Internet or ensure they are secured, especially when accessible, to prevent unauthorized access.
• Include Security Headers in HTTP Responses: Implement security-related HTTP headers to instruct browsers on handling responses, such as directives against caching, framing, and content type security.
• Apply the Cross-Origin Resource Sharing (CORS) Standard: Use CORS headers to control which cross-domain requests are allowed, ensuring your REST API specifies permitted origins.
• Avoid Sensitive Data in HTTP Requests: Do not include sensitive information, like passwords or API keys, in the URL to prevent exposure in web server logs.

Uncover OWASP and Pynt Top 10 API Vulnerabilities Automatically

The increasing reliance on APIs as the backbone of modern digital infrastructure has elevated their attractiveness as targets for malicious attacks.

We advocate for a proactive approach to API security, emphasizing early integration of security measures in the development lifecycle. By shifting left and prioritizing preventative measures, organizations can identify and mitigate vulnerabilities before they can be exploited.

Learn more on how Pynt unlocks OWASP top 10 API risks compliance.