Web Service and API Security Testing Service

What Is API Security Testing?

An API (Application Programming Interface) is the software component that lets applications, mobile devices, web services and third-party systems exchange data securely. Today the majority of banking, e-commerce, healthcare, public sector, defence and cloud-based applications run on API services.

API security testing (API penetration testing) is a comprehensive penetration testing service that assesses the security posture of REST APIs, SOAP web services, GraphQL APIs, gRPC services and other web services.

The assessment covers far more than the endpoints: authentication mechanisms, authorisation controls, input validation, business logic, session management, rate limiting, cryptographic implementation and server-side security controls are all analysed using genuine attacker techniques.

The objective is to identify and verify the vulnerabilities that would allow an attacker to gain unauthorised access through the API, reach sensitive data, manipulate systems or interrupt services.

SecureSys API security tests are conducted in line with the OWASP API Security Top 10, the OWASP Web Security Testing Guide (WSTG), NIST, PTES and other international security standards.

Why Should You Run an API Security Test?

In modern software architecture, APIs form the most critical communication layer between client applications and back-end systems. Mobile apps, web applications, microservices, IoT devices and third-party integrations all depend directly on API services.

A single vulnerability in an API service can lead to:

• Unauthorised data access
• Authentication mechanisms being bypassed
• Privilege escalation attacks
• Customer data being exposed
• Financial loss
• Loss of business continuity
• KVKK and GDPR breaches
• Damage to brand reputation

API security testing is therefore an indispensable part of modern application security.

Scope of Web Service and API Security Testing

SecureSys API security testing is not limited to checking a set of endpoints. The engagement is planned to cover every security component across the API lifecycle.

The principal areas within scope:

• REST API security testing
• SOAP web service security testing
• GraphQL API security testing
• gRPC service security testing
• JSON-RPC services
• XML web services
• OpenAPI (Swagger) analysis
• API gateway security
• Microservice security
• Webhook security
• Third-party API integrations
• Mobile application API security
• Cloud API services

API Technologies Tested

SecureSys specialists carry out security assessments across web service and API platforms of differing architectures.

REST API

• JSON-based REST services
• HTTP GET / POST / PUT / PATCH / DELETE
• JWT authentication
• OAuth 2.0
• OpenID Connect

SOAP web services

• SOAP XML
• WSDL
• XML schema
• WS-Security
• XML signature
• XML encryption

GraphQL API

• Query
• Mutation
• Subscription
• Resolver security
• Query complexity
• Depth limiting

gRPC

• Protocol Buffers
• HTTP/2
• Service authentication
• Mutual TLS
• Streaming services

API Gateway

• Kong
• NGINX
• Apigee
• Azure API Management
• AWS API Gateway
• Traefik
• Spring Gateway

API Vulnerabilities (OWASP API Security Top 10)

API services are among the most critical components of a modern application. Most mobile apps, web applications, microservice architectures and third-party integrations run through APIs, which is why API vulnerabilities are among the weaknesses attackers target most.

SecureSys API security testing performs comprehensive analysis across authentication, authorisation, input validation, business logic and server security — with the OWASP API Security Top 10 as the primary reference.

API1:2023 — Broken Object Level Authorization (BOLA)

Broken Object Level Authorization is one of the most critical and most widespread weaknesses in API security. It occurs when a user who should only be able to reach their own data is able to access objects belonging to other users.

For example, if a request sends /api/orders/1255 instead of the user's own /api/orders/1254 and the system fails to perform the necessary authorisation check, the attacker can read another customer's order details.

Controls tested

• Object authorisation
• IDOR (Insecure Direct Object Reference)
• Authorisation controls
• User isolation
• Role validation
• API access policy

API2:2023 — Broken Authentication

Broken authentication covers the critical weaknesses that arise when authentication mechanisms are implemented inadequately in an API service.

Weak authentication leads to account takeover, session abuse and unauthorised access.

Principal areas tested

• JWT security
• OAuth 2.0 configuration
• OpenID Connect
• Session management
• MFA controls
• Token lifetime
• Refresh token security
• Brute force protection

API3:2023 — Broken Object Property Level Authorization (BOPLA)

Here the user may legitimately have access to an object, but should not be able to reach every field within it.

If a user can view their own profile but the API response also returns salary, role or security settings that only administrators should see, sensitive data is disclosed.

Controls analysed

• Sensitive data filtering
• Response validation
• JSON response analysis
• Role-based data access
• Property-level authorisation

API4:2023 — Unrestricted Resource Consumption

This category covers design flaws that allow an API to consume processor, memory, database or network resources without limit.

For example:

• Unlimited pagination
• Large file uploads
• Unbounded queries
• Heavy filtering operations

can all exhaust system resources.

Controls tested

• Rate limiting
• Throttling
• Pagination
• Upload limits
• Timeouts
• Query limits

API5:2023 — Broken Function Level Authorization (BFLA)

BFLA arises when access controls are not correctly applied per user role.

If ordinary users can call API functions intended only for administrators, the risk is severe.

For example:

POST /api/admin/createUser

If a standard user can execute this, a critical authorisation flaw exists.

Controls analysed

• Role-Based Access Control (RBAC)
• Privilege escalation
• Function-level authorisation
• Admin endpoint security

API6:2023 — Unrestricted Access to Sensitive Business Flows

Some API operations act directly on business processes.

For example:

• Creating coupons
• Placing orders
• Transferring money
• Resetting passwords
• Sending SMS messages

If these can be invoked without limit, attackers will abuse them.

Scenarios tested

• Business logic controls
• Abuse case analysis
• Rate limiting
• CAPTCHA
• Fraud controls

API7:2023 — Server Side Request Forgery (SSRF)

In an SSRF attack, the API server itself is used by the attacker to send requests to other systems.

That can put critical systems at risk, including:

• Cloud metadata
• Internal network systems
• Docker services
• Kubernetes API
• AWS metadata

Controls tested

• URL validation
• Internal network access
• Metadata protection
• Outbound filtering

API8:2023 — Security Misconfiguration

A misconfigured API service hands the attacker a significant advantage.

We analyse conditions such as:

• Debug mode left enabled
• Swagger exposed
• Test endpoints
• Default credentials
• Incorrect CORS
• Incorrect HTTP headers

API9:2023 — Improper Inventory Management

Older API versions built up over the years are frequently forgotten.

APIs no longer in use may still be exposed to the internet.

SecureSys testing identifies:

• Shadow APIs
• Deprecated APIs
• Legacy versions
• Test services
• Development endpoints

API10:2023 — Unsafe Consumption of APIs

The third-party API services an organisation consumes create risk of their own.

Integrations such as:

• Payment services
• Shipping services
• SMS services
• Identity services
• Mapping services

must be consumed securely.

Controls tested

• Input validation
• Response validation
• SSL/TLS
• Timeouts
• Error handling
• Secure integration

Vulnerabilities Tested Beyond the OWASP API Security Top 10

SecureSys API security testing is not limited to the OWASP API Top 10. Advanced techniques used by real attackers and sector-specific risks are assessed just as thoroughly.

Authentication and authorisation

• Broken authentication
• JWT manipulation
• OAuth 2.0 weaknesses
• OpenID Connect flaws
• Session hijacking
• Token replay
• MFA bypass
• Privilege escalation

Data Security

• Sensitive data exposure
• JSON manipulation
• XML injection
• Mass assignment
• Parameter pollution
• Insecure deserialisation

Injection Flaws

• SQL injection
• NoSQL injection
• LDAP injection
• XPath injection
• Command injection
• CRLF injection
• Template injection

API Business Logic Flaws

• Race conditions
• Business logic bypass
• Coupon abuse
• Payment manipulation
• Workflow manipulation
• Price manipulation
• Quantity manipulation

Service Security

• CORS misconfiguration
• HTTP header security
• Missing rate limiting
• API gateway security
• Cache poisoning
• Webhook security
• File upload security
• Gaps in logging and monitoring

REST API, SOAP, GraphQL and Web Service Security Testing

SecureSys API security testing is not tied to a single API architecture. Every web service technology, communication protocol and API architecture the organisation uses is assessed against international security standards.

Because each technology carries different risks, test scenarios are planned around the architecture in use and supported by manual verification.

REST API Security Testing

REST APIs are the most common communication method in web applications, mobile applications and microservice architectures today.

SecureSys REST API security testing performs the following checks:

• Endpoint security
• JWT security
• OAuth 2.0 and OpenID Connect controls
• Authentication and authorisation testing
• BOLA and BFLA analysis
• Input validation
• Rate limiting
• Business logic testing
• HTTP header security
• CORS configuration
• Error handling
• Secure data transport (TLS)

SOAP Web Service Security Testing

SOAP web services remain widely used in enterprise applications, and their XML-based structure carries a distinct set of risks.

Testing covers:

• XML injection
• XXE (XML External Entity)
• WSDL security
• WS-Security configuration
• XML signature validation
• XML encryption controls
• Authentication and authorisation
• Secure communication
• Error message analysis

GraphQL API Security Testing

GraphQL offers flexible querying, but misconfiguration can introduce serious vulnerabilities.

SecureSys specialists assess:

• Query depth analysis
• Query complexity testing
• Resolver security
• Introspection controls
• Authorisation testing
• Data leakage analysis
• Rate limiting
• DoS and DDoS resilience
• Business logic security

gRPC Security Testing

gRPC services deliver high performance in microservice architectures, but secure configuration is critical.

The principal areas tested:

• Protobuf message security
• Mutual TLS (mTLS)
• Authentication
• Authorisation
• Service isolation
• Rate limiting
• Error handling
• Secure service communication

Webhook Security Testing

Webhooks are important integration components that move data automatically between systems.

Webhook security testing analyses:

• Signature verification
• Unauthorised requests
• Replay attack scenarios
• Token security
• Source validation
• Data integrity checks

What You Receive at the End of an API Security Test

Once testing is complete we prepare detailed reports the technical team can act on directly, together with a summary assessment for senior management.

The deliverables:

• Executive summary
• Technical API security test report
• Mapping to the OWASP API Security Top 10
• CVSS risk scores
• Verified findings with proof of concept
• Affected API endpoints
• Authentication and authorisation analysis
• Business logic security findings
• API architecture risk assessment
• Prioritised remediation recommendations
• Retest results

Continuous API Security Analysis with the Kalkan Platform

API infrastructures evolve constantly and new versions go live regularly. API security should therefore not be limited to a single test at the end of a project.

The Kalkan Cyber Security Platform, developed by SecureSys, is a central security management platform that analyses API services at regular intervals, monitors newly published endpoints and assesses security risk on an ongoing basis.

Through the platform you can track API security continuously with:

• Periodic API security analysis
• Discovery of new API endpoints
• Shadow API detection
• Swagger / OpenAPI analysis
• OWASP API Security Top 10 checks
• Risk trend analysis
• Management dashboards
• Technical reporting
• Central security management

Which Organisations Need API Security Testing?

Web service and API security testing is critical for any organisation exchanging data over the internet.

It matters particularly for:

• Banks and financial institutions
• FinTech companies
• E-commerce platforms
• Insurance companies
• Public sector institutions
• Healthcare providers
• Defence industry
• Telecom operators
• SaaS and cloud service providers
• Software development firms
• Mobile application developers
• Organisations using microservice architecture
• IoT and smart device manufacturers

For all of these, API security testing is a critical control for data security, service continuity and regulatory compliance.

Why SecureSys?

API security cannot be assessed with automated vulnerability scanners alone. Critical risks such as business logic flaws, Broken Object Level Authorization (BOLA), Broken Function Level Authorization (BFLA), mass assignment and authentication weaknesses all require hands-on expertise.

At SecureSys we do not limit API security testing to technical checks. We also evaluate the application's business processes, user roles, data flows and third-party integrations, producing comprehensive analysis from a genuine attacker's perspective.

Across REST APIs, SOAP web services, GraphQL, gRPC and webhook architectures, we work to international security standards — the OWASP API Security Top 10 foremost among them — and deliver verified findings with remediation guidance you can act on.

The SecureSys Difference

• Expert penetration testing under TSE TS 13638
• Testing aligned with the OWASP API Security Top 10 and OWASP WSTG methodologies
• REST API, SOAP, GraphQL, gRPC and webhook security testing
• Manually verified business logic and authorisation flaws
• Comprehensive analysis focused on authentication, authorisation and data security
• Findings verified using genuine attacker techniques
• Detailed reporting at both technical and executive level
• Risk prioritisation with actionable remediation guidance
• Post-remediation retest support