Your REST API might be leaking more than you think
REST APIs quietly run the show behind most modern software: websites, mobile apps, desktop tools, cloud platforms, and business systems all lean on them to move data around and get things done. That’s exactly why a weakness there matters so much. An API is often the shortest path to your data, and if that path isn’t locked down properly, an attacker doesn’t need to break in anywhere else.
A REST API Security Assessment is us checking that path carefully. We look at authentication, authorisation, input validation, data protection, business logic, and configuration, then tell you what’s actually exploitable and what’s just a theoretical concern.
What this actually is
Think of it as watching how your API behaves under pressure, not just whether it technically works. We look at how it handles requests, how it checks who’s asking, how it controls what they’re allowed to see or do, and how it talks to everything else it’s connected to.
Depending on your setup, that can cover authentication, authorisation, access control, object-level permissions, input validation, endpoints, HTTP methods, tokens and sessions, rate limiting, sensitive data exposure, error handling, business logic, configuration, security headers, encryption, and any third-party integrations.
The real question we’re answering: could someone manipulate a request and get access to something, or do something, they were never supposed to?
Why this matters more than people think
APIs usually sit in the middle, between your applications and the systems behind them. That means they often have direct access to customer accounts, transactions, databases, and core business processes. A weakness in the API rarely stays contained to the API. It tends to be the door to everything else.
This kind of testing helps you find vulnerabilities before they’re found for you: broken authentication, weak authorisation, data leaking out where it shouldn’t, insecure endpoints, sloppy token handling, missing input validation, no rate limiting, business logic that can be gamed, and configuration nobody double-checked.
What we actually look at
Mapping the API. Before testing anything, we need to understand what’s there. Endpoints, HTTP methods, parameters, request and response formats, authentication flows, key workflows. This gives us a real picture of the attack surface, not a guess.
Authentication. Can the API actually confirm who’s asking? We test API keys, OAuth, JWT tokens, session tokens, MFA flows, token expiration, and whether authentication can be bypassed or is simply weak to begin with.
Authorisation. Being authenticated tells the API who you are. It doesn’t automatically mean you should see everything. We test different roles and access scenarios, looking for broken object-level or function-level authorisation, privilege escalation, role manipulation, and access to data that isn’t yours.
Broken object-level authorisation, specifically. This one deserves its own spotlight because it’s so common and so dangerous. APIs love using IDs, account numbers, order numbers, document numbers. If changing one of those numbers in a request lets you see someone else’s data, that’s a serious problem, and it can exist even when authentication itself is working perfectly.
Input validation. Every parameter, request body, and header is a potential entry point. We test whether they can be pushed into unexpected behaviour, injection, data manipulation, validation bypass, or server errors that leak more than they should.
HTTP methods. GET, POST, PUT, PATCH, DELETE, each one needs its own protection. We check whether a user who should only be able to view something can also quietly modify or delete it.
Tokens and sessions. We look at how tokens get issued, sent, stored, checked, and expired. Reuse, manipulation, weak handling, access after logout, tokens that never seem to expire, all of it gets tested.
Data exposure. APIs are notorious for returning more than the client actually needs, personal details, internal IDs, config data, even credentials or tokens buried in a response nobody thought to check.
Rate limiting. Can your API be hammered with requests? We check for protection against brute-force attempts, automated abuse, and resource exhaustion.
Business logic. Not every vulnerability is a coding mistake. Sometimes the process itself can be gamed, steps skipped, values changed mid-transaction, actions repeated that should only happen once, rules bypassed entirely.
Error handling. Error messages can accidentally hand over a map of your system, internal paths, database details, software versions, debug output, stack traces. We check what your API is quietly revealing when something goes wrong.
How we run the assessment
Scope and planning. We start by understanding your API environment, whatever documentation exists, authentication requirements, user roles, and endpoints, then agree on exactly what’s in and out of scope.
API discovery. We go through documentation and actual behaviour to map endpoints, parameters, methods, authentication flows, and key workflows.
Authentication and authorisation testing. Using the roles and permissions available, we test whether access controls actually hold.
Vulnerability testing. We test across input validation, access control, tokens, data exposure, configuration, and business logic.
Manual validation. Anything that looks like a real issue gets manually confirmed, so you’re not chasing false positives.
Risk prioritisation. We rank findings by severity, exploitability, what’s affected, and how sensitive the exposed data is.
Reporting. You get a clear breakdown of each finding, the endpoint affected, the security impact, the evidence, and how to fix it.
Retesting. Once fixes are in, we check they actually held.
What tends to show up
Broken object-level authorisation. Broken authentication. Broken function-level authorisation. Excessive data exposure. Weak access controls. Injection vulnerabilities. Weak token handling. Missing rate limiting. Security misconfiguration. Sensitive information exposure. Insecure HTTP methods. Weak input validation. Business logic vulnerabilities. Excessive permissions. Improper error handling. Unprotected endpoints. Weak session management. Insecure third-party integrations. Outdated components. Unnecessary public exposure.
Assessment or penetration test?
These two terms get used almost interchangeably, but they’re not identical. A REST API Security Assessment tends to be a structured review of your controls, architecture, configuration, authentication, authorisation, and vulnerabilities. API penetration testing leans harder into actually attacking things, simulating an attacker and validating whether weaknesses can genuinely be exploited.
Which one you need depends on your risk level and what you’re actually trying to learn.
Not the same as a vulnerability scan
Automated scanning is fast and catches known issues, but it has no idea what your business logic is supposed to look like, or which permissions actually make sense for your users. It can’t tell that a customer viewing someone else’s invoice is a problem, it just sees a 200 response.
Manual testing fills that gap: roles, object access, business logic, authentication flows, workflows, data exposure, request manipulation. Combining both gives you a genuinely complete picture.
Who this is for
SaaS platforms. E-commerce applications. Banking and fintech platforms. Healthcare applications. Mobile apps. Customer portals. Enterprise applications. Cloud platforms. Business management systems. Payment systems. Partner integrations. Microservice environments.
It matters most wherever your API is a direct line to sensitive information or important business functions, which, honestly, describes most APIs worth having.
When to test
Before launching a new API. Before a major update. After adding new endpoints or changing authentication. After adding new user roles. When integrating a third-party service. Before connecting APIs to anything sensitive. After a big architecture change. Following a security incident. As part of regular testing, or as one piece of a broader VAPT programme.
Testing right after a change matters most, since that’s usually when something new and untested slips in.
What you actually get out of it
A stronger, more secure API. Better protection for sensitive information. Authentication and authorisation that actually hold up. Fewer insecure endpoints. Reduced risk of unauthorised access. Business logic that’s been genuinely stress-tested. Cleaner configuration. Fewer surprises in production. Prioritised, actionable findings instead of a wall of noise.
Why work with us
We test your API the way an attacker actually would, staying carefully within whatever scope we’ve agreed on. That means automated techniques backed by real manual analysis across authentication, authorisation, data handling, business logic, and configuration. Every finding gets validated, ranked by risk, backed with clear evidence, and paired with fixes your team can actually act on. And once you’ve patched things, we come back and confirm it held.
Bottom line
REST APIs are central to how modern applications work, and that makes them a genuinely serious attack surface. Authentication alone doesn’t make an API secure. Access control, input validation, data protection, business logic, configuration, and monitoring all have to hold together. This assessment finds where that isn’t happening, before someone else does.
FAQs
What is a REST API Security Assessment?
A focused security assessment of your REST API, covering the controls protecting its endpoints, data, authentication, authorisation, and business logic.
How is this different from web application testing?
Web application testing looks at the whole interface and backend. This focuses specifically on API endpoints, requests, responses, authentication, authorisation, and API-specific workflows.
Can you test our authentication?
Yes. API keys, OAuth, JWT, sessions, whatever your API uses, we test it based on your actual architecture.
Can you test authorisation too?
Yes, and it’s a core part of this. We test different user roles to see whether anyone can reach resources or functions outside their permissions.
What’s broken object-level authorisation, exactly?
It’s when an API doesn’t properly check whether the person asking is actually allowed to access a specific record. Change an ID in the request, and suddenly you’re looking at someone else’s data.
Can you test API responses for data exposure?
Yes. We check whether responses are quietly handing back more than they should.
Do you test rate limiting?
Yes, where it’s relevant to your API, checking whether it can be hammered with excessive or automated requests.
Can you find business logic problems through API testing?
Yes. Manual testing is exactly how we find requests that can be manipulated to bypass rules or perform actions they shouldn’t be able to.
Do you provide a report?
Yes. Affected endpoints, vulnerability details, evidence, risk information, and remediation steps, all in one place.
Can you retest after fixes?
Yes. We confirm the issues we found have actually been resolved.
Secure your REST APIs with a Security Assessment
Talk to Sunvak Boreal about your APIs. Let’s find out what’s actually reachable before someone else does.