Security Testing for APIs

API-Pentest

APIs are essential for communication between applications. An API pentest helps you to find security gaps and protect your customers' data.

API penetration tests are a specialized form of web pentests. APIs are often well documented, specifications are available (OpenApi, Swagger, WSDL, etc.), the attack surface is thus precisely defined and certain process steps of a penetration test can be skipped.

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& GraphQL
OAuth
& JWT
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& gRPC
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Damian Strobel - CEO DSecured

Damian Strobel

CEO

My Recommendation

API security from design to deployment

APIs are your digital backbone - and often the most attractive target. We analyze auth flows, rate limits, business logic and document how your team can sustainably prevent exploits.

API Penetration Testing

Your API handles business logic, payment flows, or customer data. An API penetration test reveals from an attacker's perspective how endpoints can be exploited - and delivers prioritized hardening measures to your team.

We combine manual testing with targeted automation: session handling, authentication and authorization models, idempotency, rate limits, and input validation are rigorously tested for vulnerabilities. You gain clarity on how robust your hardening is against realistic abuse scenarios such as account takeover, data exfiltration, or manipulation of business processes.

Scope tailored to your needs

We align test depth and roles with your use cases - including partner, mobile, or machine-to-machine access. The scope is individually defined.

Real attack scenarios

From BOLA to IDOR to business logic abuse - we document every exploit in a fully traceable manner.

Concrete recommendations

Each finding includes impact, risk, proof-of-concept, and technical fix suggestions for your engineering team.

Isn't an API pentest basically a web pentest?

Methodologically, we apply the same quality standards as in a web pentest - but the focus shifts. For you, this means: we analyze not the frontend but exclusively the interface, its authentication, and its business logic. Vulnerabilities directly impact integrations, mobile apps, or internal services; therefore, we simulate both authenticated users and external attackers without a UI.

Customers often combine web and API testing in one engagement. We help you define scope and priorities so your team can focus on the riskiest endpoints while staying within budget and timeline.

Starting point of an API pentest

We begin with your technical documentation - typically OpenAPI/Swagger, GraphQL schemas, or WSDL/SOAP descriptions. Based on this, we validate authentication paths (e.g., OAuth2, API keys, mTLS), map out the most important use cases, and agree on test data and rate-limit assumptions.

Kick-off & access: You designate contacts, provide specifications, and set up test tenants with tokens or certificates.

Analysis & exploitation: We navigate staging or production-like environments, manipulate requests and execution paths, and document every deviation with screenshots, traffic logs, and payloads.

Reporting & retest: You receive a report with CVSS ratings, management summary, and technical action plan. After fixes, we reverify individual findings - at no additional cost.

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Your data will be treated confidentially and will not be passed on to third parties.

How much does a penetration test cost?

It's difficult to tell how much a test will cost because every test is individual - but we always find a solution that fits every budget.

Go to "Costs"

How often should you have a penetration test carried out?

The frequency of a pentest depends on various factors - here is an overview.

Go to "Frequency"

What types of penetration testing are there?

The word "penetration testing" is a very general word and can describe various types of testing. An overview is available here.

Go to "Types"

How does a penetration test usually work?

The process of a pentest is usually always the same - but the steps differ depending on the type of test.

Go to "Process"
Pentest Costs: Duration Factor
Budget & Scope

Savings Potential with API Penetration Tests

We align test depth with your risk landscape. This keeps APIs with many endpoints manageable, and you invest where attacks would cause real damage.

  • Prioritize critical flows We start with endpoints handling personal data, payments, or process data and allocate manual testing budget precisely for these routes.
  • Use automation strategically Routine checks for auth bypasses, rate limits, or schema deviations run automatically - results are then manually verified.
  • Bundle retests Fix validations, short spot checks, or additional roles are conducted in bundled time windows, reducing daily rates.

We're happy to evaluate your documentation in advance and propose a mix of manual and automated checks - transparent including effort estimates. For further guidance, see our article "How much does a penetration test cost?".

Methodology for API Pentests
Approach & Transparency

Methodology for API Pentests

Our methodology combines industry standards with practical attack scenarios. You always know which steps are running and which results are already available.

  • Kick-off & threat modeling We validate scope, roles, and documentation (OpenAPI, GraphQL, WSDL) and agree on no-gos, test data, and communication channels.
  • Manual analysis & exploitation Based on the OWASP API Top 10, BOLA, business logic tests, and authorization abuse, we combine requests, tokens, and parameters.
  • Reporting & retest You receive prioritization via CVSS, PoCs with request/response, and concrete fix recommendations. Retests and alignment meetings are included.

Details on the general process can also be found in our pentest methodology.

Typical API Security Vulnerabilities

There are various types of security vulnerabilities that can be found in APIs. The examples here are real examples from past penetration tests. Here are the most common:

Insufficient Access Rights

Time and again, an endpoint is found in such tests where the access authorization check has been completely forgotten. Such errors can be easily found automatically and then analyzed manually.

IDOR

Often a simple change of a user ID in the HTTP request is enough to access other users' data. This is an IDOR vulnerability (Insecure Direct Object Reference).

Cross Site Scripting (XSS)

XSS is also found in API pentests. The special feature here is often that these are output in the context of a JS framework and identification is sometimes somewhat more complex.

Server Side Request Forgery

The attacker can make the server send requests to other servers. This can lead to the server disclosing internal information or even sending requests to internal services. Such functions should be strictly isolated if they are required.

SQL Injections

The classic - some parameter is not fully validated by the ORM and an attacker can access the database. Depending on the database system, this can quickly lead to complete takeover of the web server. Particular caution is required here.

Undocumented Routes

This is also something we often find. Developers have created a route but have not listed it in the documentation. That's a goldmine for attackers who may be able to access functions not actually intended for them.

Outdated Components

Here too there are parallels to web pentests. Outdated components are a gateway for attackers. The classic example is old software that internally exports data to PDF or crawls URLs internally.

Unexpected Behavior Leads to XXE

The majority of APIs use JSON for communication. This can lead to unexpected behavior if, for example, the application is forced to accept XML instead.

File Processing Without Validation

Upload/download/processing of files is almost always seen in web applications. The data is sent to the API and not properly validated there. The result can be manifold - in a negative sense.

How much does an API penetration test cost?

Pricing depends on number of endpoints, API types (REST, GraphQL, gRPC), authentication complexity, role matrix, and desired test depth. OpenAPI/Swagger documentation significantly reduces effort.

Quick Scan

API Security Quick Check

Automated + manual verification

$2,200 - $5,500
2-4 test days
  • OWASP API Top 10 assessment
  • Automated API fuzzing (Burp/custom scanner)
  • OpenAPI/Swagger schema validation
  • Basic authentication & authorization testing
  • Rate limiting & input validation
  • BOLA (IDOR) detection (automated)
  • Manual verification of critical findings (20%)
  • Scope: Up to 30 endpoints, 1-2 roles
Ideal for: MVP APIs, small microservices, compliance baseline, budget projects
Recommended

Comprehensive Manual API Pentest

In-depth manual API security analysis

$6,600 - $22,000
5-15 test days
  • Fully manual analysis (70-85% manual)
  • OWASP API Top 10 + business logic testing
  • BOLA/BFLA (IDOR + function-level authorization)
  • Mass assignment & parameter pollution tests
  • Advanced authentication (JWT, OAuth 2.0, API keys)
  • Authorization matrix testing (all role combinations)
  • Rate limiting bypasses & API abuse scenarios
  • SSRF, XXE, injection attacks (SQL, NoSQL, command)
  • File upload/download security
  • Undocumented endpoint discovery
  • Retest + management summary + technical report
  • Scope: 30-200 endpoints, multiple roles
Ideal for: Production APIs, SaaS backends, mobile backends, enterprise microservices
GraphQL-focused

GraphQL Security Analysis

Specialized for GraphQL APIs

$5,500 - $16,500
4-10 test days
  • GraphQL introspection & schema discovery
  • Query depth & complexity limit bypasses
  • Batch query exploits & N+1 query attacks
  • Field-level authorization testing
  • Mutation abuse & subscription security
  • Directive injection & alias abuse
  • BOLA/IDOR in GraphQL queries
  • Rate limiting & cost analysis bypasses
  • Scope: GraphQL schema with multiple resolvers
Ideal for: GraphQL-first APIs, headless CMS (Strapi, Contentful), Apollo Server, Hasura
Multi-Protocol

Multi-Protocol API Test

REST + GraphQL + gRPC + WebSocket

$8,800 - $33,000
7-20 test days
  • REST API: Full OWASP API Top 10 coverage
  • GraphQL: Schema discovery, batching, depth limits
  • gRPC: Protobuf parsing, reflection API abuse
  • WebSocket: Connection hijacking, message injection
  • Cross-protocol attacks & API gateway bypasses
  • Microservices communication testing
  • Service mesh security (Istio, Linkerd)
  • API gateway configuration review (Kong, Apigee)
  • Scope: Complex microservices architectures
Ideal for: Enterprise microservices, cloud-native platforms, multi-protocol backends

Scope factors: Pricing depends on number of endpoints, API types (REST, GraphQL, gRPC, SOAP), authentication complexity (Basic, JWT, OAuth 2.0, SAML), number of user roles, documentation quality (OpenAPI/Swagger reduces effort by 20-30%), third-party integrations, and microservices complexity. For very large API gateways (500+ endpoints, multi-region), we create individual proposals.

Endpoint-based Pricing

1-30 Endpoints

Small API: Focused scope, perfect for MVPs, single-service APIs, or prototypes. Fast turnaround possible.

$2,200 - $6,600
30-100 Endpoints

Medium API: Typical production scope with multiple resources, CRUD operations, and different roles. Balanced approach.

$6,600 - $16,500
100+ Endpoints

Large API: Enterprise microservices, complex API gateways, or multi-protocol setups. Requires extended planning.

$16,500 - $33,000

Tip: OpenAPI/Swagger documentation reduces effort by 20-30%, as we don't have to manually discover endpoints. GraphQL introspection enables faster schema analysis. Postman collections or HAR files also accelerate testing.

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We find vulnerabilities in every API - the only question is how severe they are.

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Trust through experience

Some companies we have been able to help

We've had the privilege of working with some of the world's leading companies and strengthening their IT security.

Pentest: Services

Web Application Penetration Testing

A large part of the internet is based on websites and web applications.

Vulnerability Scanning

Fully automated vulnerability scanning for your IT infrastructure or application.

Further questions and answers on the topic
"API Penetration Testing"

How should my team prepare before we start the API penetration test?

From a tester's perspective, we want to know as much as possible about your API. Documentation, especially items like the SwaggerAPI JSON, WSDL, or similar, help us better understand the API. Information about the technologies and frameworks used is also helpful for increasing test effectiveness.

What are typical security vulnerabilities uncovered in an API penetration test?

API penetration tests focus on classic web security vulnerabilities. We repeatedly see SQL injections, IDOR, and code injections. But basically anything is possible - depending on the purpose and functionality of the API.

How long does an average API penetration test take?

The duration of an API test depends on the number of endpoints, parameters, and overall complexity of the API. Most tests can be completed within 1 week. However, 2-3 weeks would not be unusual.

Can an API penetration test disrupt my running services?

Normally not, as we mostly work in an isolated test environment or during predetermined time windows with low load to avoid interruptions. We communicate closely with your IT team to prevent downtimes, etc. However, preparation for such an API pentest is always advisable.

What tools and techniques are commonly used in API security assessments?

In the case of API pentests, the tooling is primarily Burp Suite in combination with custom software packages, which, for example, aim to facilitate the import of definition files. In general, an API pentest is always a manual pentest in which a person examines every route and all parameters.

Do we receive a report after completion of the API security check?

Of course - a final report is the conclusion of a pentest project. It contains all found vulnerabilities, their risk assessment, and recommendations for remediation. We are also available to answer questions after the test.

How often should a security test for APIs be conducted?

Clear recommendation: As often as it makes sense - for example, at launch, relaunch, significant code changes, server migrations, or changes in the API structure. Most customers test their API once a year. We recommend something like Pentest as a Service to be able to intervene selectively.

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