What Are API Vulnerabilities?

Application programming interfaces (APIs) have become essential components in modern web applications. Yet as reliance on APIs increases, vulnerabilities within API code can create security risks. APIs are an easy target for threat actors seeking to gain unauthorized access, disrupt businesses, steal funds and data, and launch wider cyberattacks. Consequently, discovering and mitigating API vulnerabilities has become a critical priority for enterprise security teams.

APIs are sets of rules and protocols that enable one software application to communicate and share data with other apps and systems. APIs establish the methods and data formats to be used when requesting and exchanging information. By allowing an application to access and leverage the data and functionality of other software, APIs streamline software development, simplify integration, and promote innovation and automation.

In 2006, APIs enabled Amazon Web Services (AWS) to launch its first cloud services, providing a way for other applications and systems to take advantage of Amazon’s storage and computing infrastructure. Facebook and Twitter provided APIs that allowed developers to create apps that could interact with these social media platforms. A few years later, the proliferation of mobile phones and apps sent demand and usage of APIs skyrocketing. Today, APIs have become a foundational element of modern software development, cloud computing, and Internet of Things (IoT) infrastructure.

As APIs have become ubiquitous in application architecture, API security vulnerabilities have become an increasingly attractive attack vector for cybercriminals. API vulnerabilities are weaknesses or flaws in the code of APIs that can be exploited by hackers to gain unauthorized access, manipulate data, or disrupt services. These vulnerabilities often stem from improper implementation, inadequate security measures, and misconfigurations.

API vulnerabilities are the result of several factors.

• Complex environments: APIs typically operate in complex environments involving multiple systems and workflows, third-party integrations, and microservices. Modern applications often rely on numerous APIs, which can be highly interconnected. This makes it difficult to keep track of all API endpoints and their interactions. This complexity, especially in large-scale applications, increases the likelihood of security misconfigurations, coding errors, and improper asset management vulnerabilities that are easy for hackers to exploit. Additionally, APIs frequently need to handle a high number of requests, increasing the likelihood of errors and oversights in security practices.
• Real-time requirements: Because APIs are frequently asked to handle massive volumes of requests in real time, DevOps teams may have difficulty implementing security measures that introduce latency to performance.
• Rapid proliferation and versioning: APIs can change frequently as applications evolve. Keeping up with these changes and ensuring continuous security testing is challenging. In many organizations where APIs are constantly updated, DevOps teams may have difficulty managing security requirements as they release new versions. Additionally, the rapid pace of modern software development can lead to a failure to sufficiently test for and remediate potential security issues before the software is released.

Mitigating API vulnerabilities is crucial to maintaining the security and integrity of web applications. Unaddressed vulnerabilities can lead to unauthorized access, data breaches, and denial-of-service (DoS) attacks. Ensuring robust API security helps protect sensitive data, maintain user trust, and comply with regulatory requirements.

Failing to address API vulnerabilities can result in severe consequences, such as data breaches that expose sensitive information like personally identifiable information (PII) and financial data. This can lead to significant financial losses, reputational damage, and legal penalties for organizations.

When seeking to improve API security, IT teams face challenges both in discovering vulnerabilities and in mitigating them.

• Automated scanning limitations: Automated vulnerability scanners may struggle with APIs due to the need for proper authentication and handling of dynamic data. These tools might miss logical vulnerabilities specific to the business logic of the API.
• Authentication and authorization issues: Testing APIs for authentication and authorization flaws requires a thorough understanding of how access controls are implemented. These issues can be subtle and hard to detect.
• Insufficient documentation: Poor or outdated API documentation can hinder the discovery of vulnerabilities. Without clear documentation, it's challenging to understand the intended functionality and security requirements.
• Lack of visibility: In many organizations, APIs are developed quickly and by multiple teams with no centralized framework for managing security. In these environments, security teams are unlikely to be aware of all the APIs in production, making it impossible to visualize, evaluate, and secure them all. Shadow APIs (undocumented or forgotten APIs) can be particularly problematic as they may not be properly monitored or secured.
• Design flaws: Many vulnerabilities stem from design flaws that are not easily fixed by patching. Addressing these issues often requires significant changes to the application architecture.
• Security testing integration: While incorporating security testing into the continuous integration and continuous deployment (CI/CD) pipeline is essential, it can be difficult to achieve without slowing down development processes.

API vulnerabilities encompass a range of security weaknesses. Many key API vulnerabilities are outlined by the OWASP API Top 10. The list below identifies the issues that lead to those vulnerabilities in the first place.

Inadequate authentication and authorization

In API security, when an entity like a user, device, or application tries to access an API, authentication is the process of determining whether that entity is legitimate and trustworthy — or whether it’s malicious. After an entity is authenticated, authorization is the task of determining what level of access it’s permitted to have with the API. When authentication and authorization mechanisms are weak or improperly implemented, it can lead to significant API vulnerabilities. For example, a poorly secured API endpoint might allow unauthorized users to gain access to sensitive data by exploiting flaws in the authentication process.

For example, broken object level authorization occurs when IT teams improperly implement access control, allowing unauthorized users to access or manipulate sensitive data. Function level authorization is when there are inadequate authorization checks for specific functions or operations within an API. User authentication flaws are the result of weak authentication mechanisms, such as insufficient use of multi-factor authentication (MFA).

Lack of input validation

APIs that do not properly validate input can be susceptible to various types of attacks. Threat actors may use inputs to inject malicious SQL queries into API requests to manipulate databases, or they may inject malicious scripts into API responses that can be executed in the user's browser. SQL injection and cross-site scripting (XSS) are some of the most common types of injection attacks.

Misconfiguration

APIs frequently have complex configurations that make them more customizable — but also make it harder to accurately configure security controls. When administrators miss these configurations or don’t follow best practices, it opens the door for a variety of attacks.

Lack of limits

When APIs don’t set adequate limits on resource consumption, attackers may make excessive requests that consume most or all of API’s network bandwidth, memory, CPU, or storage resources. This may cause the API to stop working or slow down, denying service to legitimate users and increasing costs. APIs may also fail to limit requests from one client, potentially leading to denial-of-service (DoS) attacks or distributed denial-of-service (DDoS) attacks.

Inadequate user/URL validation

When user-provided URLs are not adequately validated before an API fetches resources from another server, malicious actors may make the API server send requests to unintended locations to bypass firewalls or access internal systems. This is called server-side request forgery (SSRF).

Exposing data, business processes, and endpoints

Excessive data exposure occurs when API responses include information that API requests didn’t ask for, potentially giving attackers information they can use to gain unauthorized access. APIs also frequently expose business processes like posting comments or purchasing items without adequately controlling how these processes might be abused. This allows attackers to misuse these functionalities to cause disruption and adverse events. Additionally, APIs may expose more endpoints than necessary, allowing attackers to exploit outdated, deprecated, or unsecured endpoints and versions of APIs that developers have lost track of.

Security teams may discover API vulnerabilities using several methods.

• API security testing: Conducting regular testing can identify vulnerabilities in API endpoints, and responses can protect the entire API lifecycle. 
• Comprehensive API discovery: The inability to see an API means the inability to protect it, so discovery is often the first step to finding vulnerable APIs. 
• Real-time traffic monitoring: By continuously monitoring API traffic, IT teams can identify unusual patterns that could indicate an attempted attack on an API vulnerability.
• Code reviews: Regular reviews of API code help IT teams to identify and fix security issues.
• Security audits: Regular audits enable IT teams to assess the overall security of an API. Audits include reviewing configurations, access controls, and compliance with security policies and standards.

Mitigating API vulnerabilities involves robust security measures, API security solutions, and API best practices:

Implement strong authentication and authorization

Properly authenticating and authorizing clients is critical to preventing exploitation of API vulnerabilities.

• Multi-factor authentication (MFA): Enforce MFA to ensure that a user’s identity is verified through multiple methods.
• OAuth and JWT: Use secure authentication frameworks like OAuth and JSON Web Tokens (JWT) to manage user sessions and permissions effectively.
• Access control: Enforce strict access control policies to limit access to sensitive data and functions.

Input validation and secure coding

• Input validation: Validate all input data to prevent injection attacks and ensure data integrity.
• Sanitization: Sanitize user inputs to remove potentially harmful data.

Deploy rate limiting and throttling technology

• Rate limiting: Limit the number of requests that can be made to an API within a certain time frame to prevent abuse and mitigate DDoS attacks.
• Throttling: Implement throttling to control the load on the server side and ensure that the API remains responsive under heavy traffic.

Secure development practices

• Secure coding practices: Follow secure coding guidelines and standards to minimize vulnerabilities.
• Proper headers configuration: Set security headers correctly to protect against common web vulnerabilities.
• DevOps integration: Incorporate security solutions, like API testing, into the DevOps pipeline to ensure that security is considered at every stage of development.
• Training: Educate API developers on API security best practices and the importance of following secure coding standards.
• OWASP Top 10: Familiarize developers with the OWASP API Security Top 10 to understand common vulnerabilities and how to address them.

Continuous monitoring and testing

• API security testing: Regularly test APIs for vulnerabilities using automated tools and manual reviews.
• Real-time traffic monitoring: Continuously monitor API usage and traffic patterns to detect and respond to unusual activity promptly.

Security configurations and encryption

• Encryption: Use Transport Layer Security (TLS) to encrypt data in transit.
• Proper configuration: Ensure that APIs are properly configured with secure settings and defaults.