APIs enable seamless communications between different software systems. But with great flexibility comes insecurity. Here’s what you need to know about API security testing.
There’s a reason why Application Programming Interfaces (APIs) are often described as “The backbone of modern applications”: They play a crucial role in enabling different software systems to communicate with each other seamlessly.
From a software development point of view, this has been transformational: Developers can integrate functionality into their software applications without having to build complex features from scratch or understand the internal workings of the API. This simplifies the process of building feature-rich applications, even in accelerated software development lifecycles (SDLCs).
APIs: Where Flexibility Meets Vulnerability
Unfortunately, the functionality that makes APIs so useful also makes them an attractive target for cyber attackers. One software developer’s gateway to data and services is an attacker’s key to the kingdom: Their widespread use and direct access to multiple applications makes APIs an ideal attack vector. For an idea of what that means in the real world, look no further than one of the biggest data breaches of recent times.
The MOVEit data breach impacted more than 2,500 organizations and over 67 million people worldwide. Attackers exploited a SQL injection vulnerability in the MOVEit Transfer web application, enabling them to interact with MOVEit’s APIs. From there, they were able to exfiltrate sensitive data and access credential details, gaining superuser access to administrative rights within the application.
By leveraging the API, the MOVEit attackers were able to make API calls to access file information and download data without authorization. Lessons learned in the aftermath have made MOVEit both a poster child for what can go wrong, as well as a case study underscoring the importance of API security testing. So, how can you make APIs more secure?
What is API Security?
As we’ve seen, API vulnerabilities can become a significant entry point for attackers. Effective API security management is essential for mitigating the risks posed by custom and third-party APIs. It involves regular API testing and processes that help protect APIs from threats and potential vulnerabilities. The testing process includes monitoring API traffic at various API routes, enforcing security policies, and ensuring that APIs adhere to security standards.
API security and API security testing tools help ensure that APIs function securely, safeguarding the integrity, confidentiality, and availability of the data they handle. This includes user authentication, access authorization, input validation, and traffic monitoring to detect and remediate potential API threats.
Why is API Security Testing Important?
As the MOVEit breach underlined, the far-reaching risks of vulnerabilities in the software supply chain: many of the organizations affected were impacted indirectly, through third-party vendors using the MOVEit software. The sheer scale of the vulnerability risk was underscored by the fact that, on initial discovery, researchers were able to identify 1,567 breach notifications related to MOVEit. Insecure software supply chains and mass exploitation by cyber attackers are a perfect match – and no one knows this better than adversaries.
Let’s take a look at some of the most common risks attackers exploit.
What Are the Most Common API Security Risks?
Common API security risks include:
- Injection attacks: Malicious code is injected into an API, allowing attackers to manipulate operations or gain unauthorized access to data.
- Weak/broken authentication: Weak authentication mechanisms and poor access control enable adversaries to exploit the identities and credentials of legitimate users.
- Exposed data/API leaks: Unsecured APIs can unintentionally expose sensitive data through misconfiguration, weak authentication, or any of the security weaknesses described in this list.
- Insecure API keys: Hardcoded, leaked or publicly available API keys can be exploited to gain unauthorized access to sensitive systems and data
- Rate limiting issues: APIs without request limits can be exploited for mass data exfiltration, data scraping, or denial-of-service (DoS) attacks.
Because they often provide structured access to sensitive or critical data, API leaks, in particular, are an attractive attack vector for cybercriminals. High-profile examples of API leaks in recent years include:
- Facebook: A misconfigured API exposed millions of user records in 2019.
- T-Mobile: Personal data of 37 million customers was scraped by attackers exploiting an API vulnerability in 2023.
- Twitter: Account data was leaked via a public API flaw in 2022.
How does API security work, and how does it help prevent breaches?
How Does API Security Work?
The key components of API security are authentication, authorization, input validation, and continuous monitoring. A comprehensive API security strategy includes:
Authentication and authorization: These steps involve identity confirmation, and verifying the identity of users or systems interacting with the API. Authorization ensures that only authenticated users or entities have the permissions needed to access specific resources, services, or systems.
Input validation and filtering: This helps prevent injection attacks, ensuring data integrity. API inputs are validated and sanitized to prevent malicious payloads such as XSS or SQL injection.
Rate limiting and throttling: By controlling API traffic (i.e., the number of requests sent to/from an API), defenders can prevent malicious overloading such as DoS attacks, along with brute-force attacks and API scraping.
Access control and least privilege: Measures such as role-based access control (RBAC) and attribute-based access control (ABAC) ensure users can only access data they’re authorized for.
Monitoring and logging: By continuously monitoring API interactions using dedicated API security tools, security teams can detect anomalies and respond to potential security breaches quickly.
From an AppSec and software development perspective, working to eliminate vulnerabilities early in the software development lifecycle (SDLC) can go a long way to ensuring that APIs are more secure. Implementing API security testing in CI/CD (continuous integration/continuous delivery) can help to significantly reduce the risks.
What is API Security Testing?
API security testing is the process of analyzing and evaluating APIs to identify the vulnerabilities, weaknesses, and potential security risks we’ve just discussed. API security tools proactively scan for flaws, enhancing the security of API interactions across business flows. By integrating API testing into CI/CD pipelines, AppSec and developer teams can automate testing, and detect vulnerabilities early in the development process, before they become a problem. Some examples of API vulnerabilities teams can test for include: input validation and injection testing, business logic testing, rate limiting testing, security misconfiguration testing, and authentication/authorization testing.
The Benefits of API Security Testing Tools
As multiple breaches have demonstrated, APIs present an attractive attack vector to adversaries looking to access sensitive data or achieve lateral movement within software supply chains. In this context, a clear benefit of using API security testing is its capacity to enable early detection and mitigation of vulnerabilities.
What does that mean in terms of real-world benefits?
- Meet compliance requirements: Many industries have strict data protection laws requiring API security, among them GDPR, PCI-DSS, and HIPAA. Using an API security solution will help unveil misalignment with requirements.
- Prevent API-specific attacks: API calls account for a significant volume of web traffic, making them an easily available, attractive target for adversaries. Using API tools to identify these web security risks is a must.
- Prevent data breaches: APIs handle sensitive data – everything from credentials to sensitive customer information. Securing environments, the connectors (i.s., APIs), and the software itself helps mitigate the risks of a breach.
- Improve performance: By implementing measures such as rate limiting, teams can reduce downtime and performance lags caused by excessive traffic.
If a lot of this sounds very familiar in AppSec terms, that’s because there’s a lot of overlap in security goals, the need to collaborate with software development teams, and the consequences of software vulnerabilities for overall supply chain security. But there are some important differences between API security and general AppSec.
Application and API Security: How Are They Different?
Application Security is focused on protecting entire applications, whereas API security zones in on vulnerabilities specific/unique to their role as interfaces between systems.
Vulnerabilities such as broken object-level authorization (BOLA), mass assignment, server-side request forgery (SSRF), API-specific injection attacks, and unrestricted resource consumption all call for security measures specifically tailored to API vulnerabilities. To help AppSec teams understand where to focus their efforts, the Open Web Application Security Project (OWASP) provides a list of the top API security risks.
OWASP API Security Top 10
In response to the rapid growth in API use, the OWASP API Security Top 10 list was launched in 2019, and updated in 2023. Overall, the list reflects the ways in which both APIs and the threats are evolving – illustrated by the addition of SSRF, Unrestricted Access to Sensitive Business Flows, and Unsafe Consumption of APIs.
As with general AppSec vulnerabilities, we see persistent vulnerabilities in the form of BOLA and broken authentication – repeat offenders that can be seen as low-hanging fruit for remediation and attackers alike. The list also underlines the prevalence of authorization-related vulnerabilities – and the associated need for more robust access controls.
REST API Security vs SOAP Security
When it comes to building APIs, Representational State of Resource (REST) and Simple Object Access Control (SOAP) are two widely used protocols. But their different architectures mean they have different security requirements – and different strengths. For example, SOAP’s message-level encryption makes it inherently more secure than REST, which requires additional security measures. As such, SOAP is considered more suitable for high-security transactions such as banking or healthcare; REST is easier to implement, making it a preferred option for web APIs, mobile apps, and IoT.
Both SOAP and REST have been the target of significant breaches, including the Trello breach (REST) and Delinea Secret Server (SOAP) in 2024. Some of the key differences between SOAP security and REST security are:
SOAP: Provides message-level encryption, authentication, and integrity checks.
From a data protection perspective, SOAP encrypts the entire message – even if it’s intercepted, the message remains secure.
REST: Relies of HTTPS (TLS — transport layer security) for encryption, along with API, OAuth2 or JWT keys for authentication. Because it only encrypts the transport layer, data can be exposed and/or decrypted in transit.
Bottom line: SOAP is considered the best option for high-security transitions, while REST’s easier implementation and scalability make it the preferred choice for Web APIs and mobile applications.
What About GraphQL Security?
SOAP and REST aren’t the only two security testing methods in town: GraphQL is used in complex data scenarios, where its capacity to allow users to specify exactly what data they need makes it a more efficient, resource-friendly option.
Not for the first time, however, we see that flexibility comes with a security-related price tag: GraphQL’s powerful query flexibility can become an increased attack surface, not least from a rate-limiting perspective, where the scope for abuse could have serious impact. It is also important to validate user inputs to prevent injection attacks or unauthorized data access, which is a common focus in dynamic API security.
Bottom line: Because of its flexibility and use in complex data scenarios, GraphQL poses unique security challenges. GraphQL security measures include:
- Rate limiting and query depth restriction
- Authentication and authorization
- Input validation and query whitelisting
- Allowlist and batching control
Now that you’ve got an idea of the security requirements for widely used approaches — what are some of the API security testing methods and tools to consider?
API Testing Methods and Tools
Every line of code has the potential to be a security vulnerability, and APIs are no different from other software applications. When it comes to API security assessment and testing, many of the security tools we’re familiar with from AppSec also come into play: Dynamic Application Security Testing (DAST), Static Application Security Testing (SAST), and Software Composition Analysis (SCA).
Let’s take a very brief look at what each of these can do as part of your API security testing methodology:
SAST tools: Scan your code for vulnerabilities and address software security issues. Because it provides detailed insights into vulnerabilities, SAST supports developers in adopting a more security-minded approach to software development.
SCA tools: Scan open-source and third-party code and dependencies for potential security issues that can lead to breaches. Because it tracks license requirements, SCA helps mitigate compliance risks related to open-source components.
DAST tools: Take an attacker’s approach to code, simulating attacks on applications to expose vulnerabilities. DAST helps identify security gaps in code or identify unforeseen outcomes that could have a downstream effect on application security.
SAST, DAST, and SCA tools can all be automated or performed manually. In a best practice environment, it’s less about either/or and more about leveraging the tools in a complementary way to give developers and AppSec teams the insights they need to build more secure applications and APIs.
API Security Best Practices
As we’ve seen, API security testing is an essential part of AppSec, with its unique challenges and requirements. To test API security, and ensure that errors aren’t introduced during software development, incorporating API security into the SDLC helps to ensure best practice and strengthen overall security.
Some API security best practices — and what they can look like as part of a secure SDLC include:
- Adopt a secure SDLC approach: Incorporate security into every phase of the software development process, from design to deployment.
- Automate API security testing at each API endpoint: Automate tools such as SAST and DAST in CI/CD pipelines to catch insecure code and identify runtime vulnerabilities. Use SCA to detect third-party library risks that could lead to API abuse.
- Minimize false positives: Fine-tune and adjust SAST/DAST and other automated tools to align with real-world API behavior – use human expertise and verification to complement automated processes and ensure accuracy.
- Apply the Principle of Least Privilege (PoLP): APIs and applications generally should grant only the minimum permissions needed to perform a task. Third-party integrations should be restricted to essential permissions.
- Secure third-party API integrations: Perform API security assessments on vendors before integrating them.
- Continuous monitoring: Continuously monitor APT traffic for anomalies, and apply security patches and updates as required. Rotate API keys and credentials periodically, as part of ongoing maintenance.
By embedding a security-first approach into every phase of the API SDLC, organizations can maintain a proactive approach to AppSec.
OX Security: A Comprehensive Approach to API Security
Maintaining a secure API environment can be a daunting task. OX Security takes a comprehensive approach, integrating advanced security measures throughout the SDLC to ensure all APIs (including shadow APIs) are visible and accounted for.
For API discovery, our comprehensive inventory and monitoring capability gives defenders detailed insight into API usage, dependencies, and potential vulnerabilities, providing complete visibility over your API landscape. Integrated SAST and SCA tools ensure you’re covered for both proprietary and open-source elements, while attack path reachability analysis gives you the risk rating insights you need to focus on the 5% of threats that really matter.
See for yourself: Sign up for a free trial and learn how you can mitigate the risks associated with APIs, while protecting sensitive data and ensuring a more resilient security posture.
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