Why We Do API Testing in Cyber Security Services
An incredible thing about APIs is that they are tiny but mighty, connecting your app with other systems and services. But that’s also scary. Because one flaw in these lining elements can cause a lot of damage.
Financial Impact of Weak Security Testing for APIs
Companies can be fined for data exposure. And we’re not talking about a “slap on the wrist penalty”. For example, T-Mobile was to pay nearly $16 million after tens of millions of customer accounts were exposed. Even bigger numbers can appear when laws like GDPR or HIPAA are involved.
Organizations may face lawsuits from affected customers, partners, or shareholders. Then, you’re not just losing money. You’re wasting time as well. Because legal defense can take months, if not years. For example, T-Mobile agreed to a $350 million settlement in a class-action lawsuit. The firm really should have paid more attention to its API testing services.
Expenses will continue to pile up post-breach, too. Companies often provide identity protection services or direct financial compensation to affected users. And that can last for years. To illustrate, in the aftermath of the famous Equifax breach of 2017, the firm had to pay up to $425 million to affected customers.
What’s more, after an incident occurs, you’ll have to invest in proper remedies. Security audits, infrastructure updates, and additional security testing for APIs will be the minimum. Akamai’s report shows that the average cost of an API security breach is around $600,000 in the US and over $400,000 in the EU.
We can’t forget about the indirect expenses either.
If private data is exposed, a public outcry is almost inevitable. For example, the overly permissive nature of Facebook’s Graph API led to users boycotting the app and deleting their accounts. So, lacking API security testing services might just lead to:
- Customer churn and lost revenue.
- Damaged brand reputation.
- Increased scrutiny from regulatory bodies, etc.
To sum it up, it’s better to invest in high-grade cybersecurity services now than lose thousands or millions of dollars later.
Industry-Specific Risks of Inadequate API Security Testing
You’re bound to run into a few more challenges when it comes to APIs. Depending on your sector, compliance requirements and fines for non-adherance range dramatically.
Of course, there are cases where fines just go through the roof. That depends on the severity of non-compliance or breach and company size. But just as an example, Meta was to pay €1.2 billion for transferring European users’ personal data to the US without adequate protections.
So, when it comes to security, you need to focus on adequate testing and compliance equally.
What Is API Security Testing?
It’s time to step aside from the frankly nerve-wracking opening section. Here, we begin with our API security testing guide designed to advance your defenses. If you need a quick refresher on what application programming interfaces are, check out our brief handbook—API testing introduction. For now, we continue.
API Security Testing vs Functional Testing
First, we need to remember that a working API isn’t necessarily a secure API. Imagine a spoon with a flamethrower attached to it. You can still eat soup. But you wouldn’t feel very safe doing it. That’s why functional testing isn’t enough.
Functional tests determine whether your API does what it should:
- Does the API return correct responses?
- Are response times acceptable?
- Does error handling work properly?
And security testing looks at how it does what it should in terms of data protection and resilience:
- Can unauthorized users access protected endpoints?
- Is sensitive data properly encrypted and protected?
- Are input validation controls effective against injection attacks?
So, API security testing is the process of checking your APIs to make sure they don’t expose data or function in unsafe ways.
API Security Testing Checklist: Top Risks to Address
Fortunately, you don’t have to start from scratch or reinvent the wheel with API testing. Your niche, industry, and applicable regulations already serve as a guide regarding what to focus on. You can also turn to resources that analyze the most prevalent API threats. Let’s take a look at OWASP’s version.
OWASP Top 10 API Security Risks highlights the following issues as the most common/critical:
- Broken object level authorization—an API doesn’t properly verify that a user has permission to access or modify a specific object.
- Broken authentication—the authentication mechanisms for an API are implemented incorrectly or are weak.
- Broken object property level authorization—an API allows a user to access or modify an object’s properties even if they are authorized to access the object itself.
- Unrestricted Resource Consumption—an API doesn’t limit the amount of resources (CPU, memory, bandwidth, storage) a client can consume.
- Broken function level authorization—API fails to properly enforce authorization for different functions or roles.
- Unrestricted access to sensitive business flows—APIs expose critical business logic or workflows without sufficient protection.
- Server side request forgery—an API fetches URLs or data from other servers without validation.
- Security misconfiguration—APIs have default settings, unnecessary features, or exposed error messages.
- Improper inventory management—outdated or undocumented APIs are accessible because they’re not tracked or maintained.
- Unsafe consumption of APIs—an API consuming an external service (another API) doesn’t properly validate the data received from it.
They may seem pretty straightforward. But they may not be as easy to fix. How effectively you can handle API vulnerabilities greatly depends on the maturity of your quality processes and team skills. So, before API security testing, you should focus on teaming up with experienced specialists.
How to Do API Security Testing
There are many ways to approach API security testing. In this section, we’d like to focus on what you should definitely include in your process without trying to restrict your team. Keep in mind that, here, we’re centering on in-depth, manual assessments. They offer the most detailed inspections, which are critical in the current cyber resilience space.
Discovery and Reconnaissance
First, you need to find out what the API exposes. Identify all available functions, how they’re called, and what kind of information they return. Here, it’s common to study app behavior or monitor network traffic to uncover hidden or undocumented parts of the API. This helps create a full picture of what could potentially be attacked.
Authentication and Authorization Testing
This phase checks how the API controls who can access what. You need to make sure that users have to prove who they are and that they only get access to the parts of the system they’re allowed to use. Your team should also check whether it’s possible to get around these controls or gain access to someone else’s data.
Input Validation and Injection Testing
Here, look at how the API handles the data it receives. If the system doesn’t check inputs carefully, it might be tricked into running harmful commands or revealing information. The goal is to see if someone could send unusual or risky data that the API fails to block.
Business Logic and Rate Limiting
This step focuses on how the API behaves in real-world usage. Look for ways to misuse its features, like skipping steps in a process, repeating actions too quickly, or triggering errors that create unfair advantages. Don’t forget to test whether the API can limit repeated requests to avoid being overwhelmed.
Data Protection and Privacy
Next, ensure that the API handles sensitive information responsibly. Check if data is properly secured when sent or stored. And make sure personal or confidential information can’t be accidentally exposed. Lastly, pay enough attention to how well the system protects user privacy.
App-Specific API Security Testing
Remember that different app types introduce unique API vulnerabilities. For example, in web API security testing, the goal is to check for risks like:
- Insecure API calls from the browser.
- Exposed tokens in local storage.
- Weak client-side access controls.
In mobile API security testing, you’d focus on issues such as:
- Hardcoded API keys.
- Insecure data storage on the device.
- Improper use of authentication.
Each platform brings its own security concerns that need to be tested in context. And while on the subject of context, we should mention REST API security testing. Though the process doesn’t differ much, there are some aspects to consider.
REST APIs don’t keep track of user sessions or past activity. Each request is handled on its own, with no memory of what came before. That means the client (e.g., a mobile app) must send all required information, such as authentication tokens or user IDs, with every request.
For security testing, this means checking that:
- Every request is fully self-contained and authenticated.
- The server doesn’t accidentally rely on any hidden or leftover state.
- Sensitive actions can’t be performed just because a user made a related request earlier.
Because of REST APIs’ reliance on HTTP methods, you need to make sure that actions (GET, POST, DELETE, PUT) are used correctly. For instance:
- GET requests shouldn’t change or delete any data. Only view it.
- POST, PUT, and DELETE requests should be protected so only authorized users can create, update, or delete data.
REST APIs often use predictable URLs, like /users/1 or /orders/99. This makes it easier for attackers to guess or modify URLs to access other users’ data. That’s why you should focus on checking if unauthorized access is possible.
Sometimes APIs return more data than needed. A response might include personal details or internal system info by mistake. Here, your team ought to ensure that only the right data is shared.
To sum it up, know your product and know your APIs. Follow API security testing best practices but personalize and expand them for your project to get exactly what you want.
Manual vs Automated API Security Testing
An important thing in ensuring adequate security for your APIs is knowing when to use automated or manual testing. The former offers speed and precision. The latter presents flexibility and in-depth exploration. But both need effort and investment. So, let’s review how to apply them for best results and not spend all your budget.
Automated API Security Testing
Automation in API testing is becoming a standard. Growing app complexity and the current threat landscape drive it toward becoming a best practice. With automated checks, you can:
- Quickly test many endpoints without manual effort.
- Scan a wide range of security issues across all APIs.
- Run the same tests reliably every time, reducing human error.
- Catch vulnerabilities early in development.
- Save time and effort for security and QA teams.
- Easily integrate API testing into CI/CD pipelines for ongoing checks.
- Handle growing or changing APIs with minimal extra setup.
- Reuse test scripts across versions or projects.
- Get notified about issues during runtime, shrinking the feedback loop.
Plus, with all the tools available, you can tailor your automation to your project and budget. Below are some examples of the leading API security testing solutions.
OWASP ZAP is a free and open-source tool, fantastic for finding common security flaws. It can snoop on your API traffic and scan for common problems like SQL injection and cross-site scripting. It can even bombard API endpoints with various attack payloads. ZAP works with different API types, including REST and SOAP, and you can plug it into your development process for continuous security checks.
Burp Suite Professional is a popular and highly respected platform. Its proxy feature lets you dive deep into API requests and responses, inspecting and tweaking them. Burp Suite offers advanced features like:
- Intruder for fuzzing API parameters.
- Repeater for replaying and modifying requests by hand.
- Scanner to automatically spot a wide range of vulnerabilities.
Plus, you can extend its capabilities with add-ons from the BApp Store, giving you access to community-made tools.
Postman lets you create and manage API requests, which you can then use to build basic security tests. For example, you can craft requests to check for broken access control or validate input by sending tricky data. Postman’s scripting abilities allow for more complex test scenarios, like setting up authentication before a request. It takes a bit more manual effort to do full-on security testing. But since most developers use it anyway, it’s a handy first line of defense.
Custom security test suites are often the way to go for certain cases. If you have unique API setups, specific compliance needs, or highly sensitive data, they can be used alongside or instead of off-the-shelf tools. These suites offer unmatched flexibility. They let you precisely mimic real-world attacks, connect with your internal systems, and focus on business logic flaws. They do require more development time and ongoing upkeep. Yet, they also provide the highest level of assurance for your most important APIs.
Automation’s capabilities are vast. But they shouldn’t blind to one simple truth. Even the top API security testing solutions have their limitations.
- Automated tools often struggle with business logic flaws, which are unique to how your API works. For example, an automated tool might not catch if a user can bypass a payment step by calling API endpoints in an unexpected order.
- They can sometimes flag non-issues as bugs (false positives) or miss actual vulnerabilities (false negatives). This can happen due to test flakiness, hardcoded assumptions, or a lack of context.
- Automated scanners can’t predict or identify “zero-day” exploits—brand new, unknown vulnerabilities.
- Simulating complex, multi-step attack scenarios can be difficult for automated tools. These often require the nuanced approach of a skilled penetration tester.
- As new features are added or existing ones are modified, test scripts need to be updated regularly. This maintenance can be time-consuming, especially for large and rapidly evolving API estates.
- Testing complex authorization schemes (e.g., role-based access control, fine-grained permissions) across various user types and scenarios can be tricky to automate comprehensively.
The point is that the most effective security testing often involves human intuition, creativity, and the ability to think like a blackhat. Automated tools lack this critical element. And it’s essential for uncovering subtle vulnerabilities and novel attack vectors.
Manual API Security Testing
While manual checks are superior when it comes to the depth of exploration, we all know of their two main flaws. They’re time-consuming and resource-intensive. That’s why manual testing should be used when it’s actually needed.
- Exploring how APIs handle workflows, roles, and edge cases that automation can’t predict or abuse intelligently.
- Verifying role-based access, privilege escalation, and token handling.
- Discovering shadow APIs or endpoints not listed in the documentation.
- Securing multi-step processes (e.g., order > payment > confirmation).
- Confirming actual vulnerabilities, reducing false positives, and assessing real-world exploitability.
- Locating obscure or novel flaws.
An important thing to remember is that the effectiveness of API testing depends on the skills of the person doing it. There’s a big difference between hiring an inexperienced engineer and, say, working with API security testing vendors who specialize in the field.
#1 Professionals have the expertise to find complex business logic flaws and multi-step attack scenarios. They understand the nuances of how an API is supposed to work. So, they can craft creative ways to make it do something it shouldn’t, advancing security.
#2 Experts stay up-to-date with the latest attack techniques, emerging threats, and zero-day exploits. They can anticipate how new vulnerabilities might manifest in your unique API landscape.
#3 Experienced specialists understand your business context, compliance requirements, and the sensitivity of the data handled by your APIs. This allows them to accurately assess the real-world impact of a vulnerability. They can prioritize remediation efforts based on actual business risk, not just technical severity.
#4 Professionals provide clear, detailed, and actionable reports. They include steps to reproduce them and practical recommendations for remediation. Plus, experts present info in an understandable way, bringing teams closer and allowing for better collaboration.
#5 Security specialists offer strategic advice on how to improve your API security, implement best practices, and integrate security into your development lifecycle. They can help you build more secure APIs from the ground up.
#6 Their expertise allows for more accurate vulnerability identification. You can minimize the time wasted on chasing false positives and significantly reduce the risk of missing critical vulnerabilities.
#7 Professionals are typically well-versed in various security standards. They can ensure your APIs meet necessary compliance requirements from the start.
#8 Expert API security testing can save significant costs in the long run. It prevents costly data breaches, reputational damage, and the expensive scramble to fix vulnerabilities after they’ve been exploited.
#9 An external professional team, such as a QA company, provides an unbiased perspective. This fresh set of eyes is free from internal assumptions or blind spots that might exist within your in-house teams.
#10 Working with specialists can also be a valuable learning experience for your crew. They often share insights and best practices, effectively upskilling your internal capabilities.
Briefly, if you think your in-house skills might not secure good defenses for your APIs, consider external help. That’s just not something you’d want to cut corners with. Plus, QA outsource is a quick and cost-effective solution to finding the exact talents you want on your side.
Hybrid Approach to API Security Testing
To sum up the above discussion on manual vs automated testing—you should always combine them. Think about it this way. The two approaches offer unique benefits to your API security. So, why settle for only half of them?
That doesn’t mean that you should use manual and automated QA to their maximum. You simply need to apply them in a targeted manner to get the perks that are most valuable for your project.
- Use automated tools to quickly detect common issues like injection flaws, exposed endpoints, and misconfigured headers.
- Rely on skilled experts to explore misuse cases, role-based access flaws, and multi-step workflows.
- Integrate security tools into your CI/CD pipeline to detect regressions early and monitor API traffic for unusual behavior or emerging threats.
- Schedule periodic manual reviews and automated scans to stay ahead of new vulnerabilities, maintain compliance, and ensure long-term security posture.
And if you need guidance on figuring out the best blend of automated and manual QA for your product—we’re here to help.
Defining Your API Security Testing Frequency
As you know, testing isn’t a one-time deal. It needs to go on for as long as your product is active to upkeep and advance quality. The same applies to API security. Though it’s a little bit trickier here. Because APIs have become hackers’ sweet spot, you’re not testing application programming interfaces to maintain them. With how things are now, you’re testing your APIs to outrun attackers and find a vulnerability before they do.
In such a first-past-the-post game, testing frequency matters. A lot. That doesn’t mean, however, that you should check your APIs every second. But you definitely should figure out what schedule works for you in terms of skills, budget, and security goals. Here are key aspects to consider in your strategy:
- Risk level: APIs that handle sensitive data or critical operations need more frequent checks.
- Change velocity: the faster your codebase changes, the more often tests should run.
- Compliance requirements: regulatory standards may mandate specific testing intervals (e.g., HIPAA, PCI DSS).
- Business impact: APIs tied to revenue, customer trust, or brand reputation demand higher protection.
- Threat landscape: if your sector is a known target (like finance or healthcare), test more often.
- Available resources: budget, tools, and skilled staff affect what’s realistically possible.
- Technical architecture: complex systems, third-party integrations, or microservices increase the need for regular testing.
Most organizations go for a blend of comprehensive monthly testing and daily automated scanning. This combo offers a good balance of security coverage and resource efficiency. Yet, it might not work for you. The best solution is always a personalized one. So, you need to choose testing intervals that align with your strategy and capabilities:
- Continuous/automated testing (daily)—lightweight security scans integrated into CI/CD pipelines to catch issues early.
- Sprint/release cycle testing (every two to four weeks)—manual and semi-automated tests tied to feature releases or code pushes.
- Quarterly comprehensive assessment—in-depth reviews of the API surface, focusing on business logic, authorization, and abuse cases.
- Annual security audits—formal, external assessments (often required for compliance or stakeholder assurance).
Going with only one of the above options isn’t enough. You’ll need to mix and match these API security testing examples so that they effectively cover different threats—from common risks to advanced defenses. And figuring out your strategy isn’t going to be simple.
Suggestions on Risk-Based Frequency Adjustments
But there’s some good news. Not all APIs are equal. You won’t have to scrutinize ach and every one of them. That would be inefficient. So, you’ll be going with a risk-based approach to determine testing frequency. This will allow you to focus your efforts where they matter most.
High-risk APIs, ones that are likely to get targeted, should be tested weekly or bi-weekly:
- Payment gateways and financial transactions.
- APIs handling healthcare or personal data.
- Authentication and access control endpoints.
- Admin or privileged user interfaces.
Medium-risk APIs, ones that may not be directly exploitable but still expose sensitive operations, should be tested monthly:
- Customer account management.
- Internal business logic.
- APIs that support file handling (e.g., uploads, downloads).
Low-risk APIs, ones that serve static or public data and have limited attack surface, should be tested quarterly:
- Public-facing informational APIs.
- Read-only data services.
- Static content APIs.
Prioritizing security testing for APIs is a bit more straightforward. You’ll want to work on your cross-team collaboration to combine every specialist’s perspective (tech and business-oriented). And this amalgamation of expertise will go a long way.
Industry-Specific Recommendations for API Security Testing
Another aspect that will affect how often you test your APIs is your niche. Different industries face distinct regulatory demands, attack profiles, and traffic patterns. Our team has created a brief API security testing guide for the sectors we cooperated most with. Take a look.
Financial services:
Many institutions still rely on fixed schedules: monthly scans, quarterly reviews, and annual pentests. But this approach often misses fast-moving threats. A better solution is weekly automated scanning and monthly manual testing for critical APIs.
Healthcare:
With strict compliance and high data sensitivity, healthcare APIs need continuous automated scanning backed by monthly comprehensive reviews to stay secure and compliant.
E-commerce:
Traffic surges and seasonal promotions always carry greater risk for APIs. During high-traffic periods, adopt daily automated testing and bi-weekly manual testing. For the rest of the year, monthly manual reviews typically suffice.
SaaS and tech providers:
Fast development cycles mean security must be integrated from the start. That’s why you should apply continuous integration-based scanning paired with sprint-aligned manual testing every two to four weeks.
Keep in mind the above are recommendations based on our QA team’s experience. They aren’t the golden rule. You might need a totally different combination of approaches. And that’s fine. The important thing is that you don’t let “standards” limit your API security testing potential.
To Sum Up
Cyberattacks grow more sophisticated. Regulatory pressure intensifies. And customers demand stronger data protection. It’s truly a tough world to live in. Yet, you either adapt or get left behind. There’s no third option. Apart from risk mitigation, making API security one of your priorities shows your commitment to user safety and quality. You can build trust with your customers and set your company apart.
To get there, you should start with mapping out all APIs, assessing risks, and evaluating current testing capabilities. Next, implement basic automated scanning, set up consistent testing practices, and begin team training. And for long-term success, build a mature, continuous API security program integrated into development workflows. Most importantly, don’t stop at “good enough”. Keep improving. Threats can’t get you if you’re far in front of them.
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