CREST-Certified API Penetration Testing Services in the UK
Independent API penetration testing delivered by CREST-certified ethical hackers. Our UK-based testing team identifies exploitable vulnerabilities across REST, GraphQL, and SOAP APIs before attackers can find them.
- CREST-certified API penetration testers
- OWASP API Security Top 10 aligned testing
- Clear reporting and remediation guidance
Trusted by organisations across regulated industries including finance, healthcare, enterprise software, and critical infrastructure.
API Penetration Testing Services From OmniCyber
Our API penetration testing services help organisations identify security weaknesses in their application programming interfaces before attackers exploit them.
Using a structured testing methodology aligned with OWASP API Security standards, our testers simulate real-world attack techniques to assess how well your APIs withstand compromise. The unique challenge with APIs is that vulnerabilities often lurk beneath the user interface, making them invisible to traditional security checks.
We provide API testing services across the UK, supporting organisations that need security assurance, compliance validation, or an independent assessment of their API security posture.
When Do You Need API Penetration Testing?
Most organisations rely on APIs to power web applications, mobile apps, microservices, and third-party integrations. A professional API penetration test provides independent validation that these critical entry points can withstand real-world attack techniques.
You may need API testing services if you:
- Have launched new APIs or made significant changes to existing ones
- Are preparing for a compliance audit such as PCI DSS, ISO 27001, or SOC 2
- Process sensitive customer, financial, or health data through APIs
- Operate public-facing or third-party integrated APIs
- Have moved to a microservices architecture
- Need an independent security assessment of your API infrastructure
Our API Penetration Testing Services
OmniCyber provides a full range of API security testing services in the UK, covering modern API architectures and protocols. Our CREST-certified testers perform manual testing designed to simulate how real attackers identify and exploit API weaknesses.
REST API Testing
Comprehensive testing of RESTful APIs including authentication, authorisation, input validation, and data exposure issues across HTTP methods.
GraphQL API Testing
Specialised testing for GraphQL endpoints covering query complexity attacks, introspection abuse, and authorisation flaws unique to graph-based APIs.
SOAP API Testing
Testing of SOAP-based web services including XML injection, WSDL analysis, and authentication weaknesses in legacy and enterprise APIs.
White-Box API Testing
Full documentation provided to testers for deep, comprehensive coverage of every endpoint, parameter, and function within your API.
Grey-Box API Testing
Limited information provided to testers, simulating an authenticated user attempting to escalate privileges or access unauthorised data.
Black-Box API Testing
No prior knowledge given, simulating an external attacker discovering and exploiting your API vulnerabilities from scratch.
Mobile App API Testing
Testing the APIs that power mobile applications, including authentication tokens, session management, and data transmission security.
Microservices API Testing
Assessment of internal API communication, service-to-service authentication, and lateral movement risks across distributed architectures.
Third-Party Integration Testing
Review of how your systems consume and expose APIs to external partners, providers, and integrations.
Our API Penetration Testing Methodology
As an experienced API security testing provider, OmniCyber follows a structured and transparent methodology aligned with the OWASP API Security Top 10 and recognised application security testing standards. Our CREST-certified penetration testers combine automated analysis with expert manual testing to simulate how real attackers identify and exploit API vulnerabilities.
- Scoping and Documentation Review: We work with your team to understand the API architecture, authentication mechanisms, and business logic, reviewing API documentation such as Swagger, OpenAPI, and Postman collections to ensure comprehensive coverage.
- White-Box Testing Approach: Our testers receive full documentation and sample requests, allowing them to thoroughly assess every endpoint, parameter, and authentication flow within your APIs.
- Manual Exploitation: Beyond automated scanning, our certified ethical hackers manually test authentication, authorisation, business logic, and data handling to uncover vulnerabilities that automated tools miss.
- Risk-Based Reporting: All findings are prioritised according to likelihood of exploitation and potential business impact, helping your team focus remediation efforts effectively.
- Remediation Support: Clear remediation guidance is provided for every vulnerability, with optional retesting available to confirm fixes have closed the gap.
What You Receive From An API Penetration Test
A professional API penetration test should provide clear insight into how attackers could compromise your APIs and what actions should be taken to reduce risk.
This includes:
- Clear evidence of exploitable API vulnerabilities
- How attackers could gain unauthorised access or escalate privileges
- What sensitive data or systems would be exposed
- Which API controls fail under pressure
- What to fix first, prioritised by risk
- Clear reporting for technical and non-technical stakeholders
- OWASP API Top 10 mapping for compliance evidence
These insights are delivered in a structured report that places vulnerabilities in context, allowing your organisation to prioritise remediation and make informed security decisions.
API Testing for Compliance frameworks
Many organisations require API security testing to meet regulatory and security framework requirements. OmniCyber supports organisations preparing for or maintaining compliance with recognised standards.
This includes:
Our CREST-certified API testing helps organisations validate that API security controls are working effectively and provides the evidence required for compliance and assurance.
Common API Vulnerabilities We Identify
API vulnerabilities often go undetected because they are not visible through user interfaces. Our testing aligns with the OWASP API Security Top 10, helping organisations identify and remediate the most common and damaging API weaknesses.
Our CREST-certified testers manually verify every finding to ensure accurate, actionable results without false positives. Each vulnerability is documented with clear evidence, business impact, and remediation guidance.
This includes:
- Broken Object Level Authorisation (BOLA)
- Broken Authentication
- Broken Object Property Level Authorisation
- Unrestricted Resource Consumption
- Broken Function Level Authorisation
- Unrestricted Access to Sensitive Business Flows
- Server-Side Request Forgery (SSRF)
- Security Misconfiguration
- Improper Inventory Management
- Unsafe Consumption of APIs
What is CREST API Penetration Testing?
CREST is a recognised accreditation body for cyber security professionals and penetration testing providers. A CREST API penetration test ensures testing is carried out by qualified ethical hackers using recognised industry methodologies.
Working with a CREST-certified API testing provider gives organisations confidence that testing is performed to professional standards and is suitable for regulated or high-risk environments.
Why CREST certification matters:
- Independently assessed penetration testers
- Recognised industry testing standards
- Trusted for compliance and regulated sectors
- Professional security testing and reporting
A CREST-Certified API Testing Company You Can Trust
API penetration testing only delivers value when it is performed responsibly, consistently, and to recognised professional standards.
OmniCyber provides CREST-certified API penetration testing services delivered by experienced ethical hackers holding industry-recognised certifications including CREST, OSCP, and other offensive security qualifications.
These standards help ensure testing is accurate, ethical, and suitable for organisations operating in regulated or high-risk environments.
What Our Clients Say About Our Services
Organisations across multiple industries trust OmniCyber to deliver professional penetration testing and clear security insights.
“What stands out most is the feedback I hear after introducing others to OmniCyber. They consistently say the team are the best penetration testers they have worked with because they work with you, not just against your systems.”
Global Travel Company
Head of Security
“Your report is the most detailed and practical we have reviewed. The level of clarity and prioritisation made it easy to understand what needed attention.”
Healthcare Industry
DevOps Manager
“The work and interactions (with Louie Augarde in particular) were so impressive we wouldn’t even consider tendering elsewhere at this point.”
UK Registered Charity
IT Infrastructure Manager
Frequently Asked Questions
What is API penetration testing?
API penetration testing is a security assessment that simulates real-world attacks against your application programming interfaces. Our CREST-certified ethical hackers test authentication, authorisation, business logic, and data handling to identify exploitable vulnerabilities before attackers do. Testing is aligned with the OWASP API Security Top 10 to ensure comprehensive coverage of the most damaging API weaknesses.
How long does an API penetration test take?
Most API penetration tests take between 5 and 15 working days depending on the number of endpoints, complexity of authentication flows, and testing approach. We confirm timelines during the scoping phase so you have a clear delivery schedule before testing begins.
What is the difference between API testing and web application testing?
Web application testing focuses on the user-facing interface, while API testing examines the backend services that power applications, mobile apps, and integrations. APIs often have unique vulnerabilities such as broken object level authorisation and excessive data exposure that web app testing alone may miss.
Do you test REST, GraphQL, and SOAP APIs?
Yes. Our team has experience testing all major API architectures including REST, GraphQL, SOAP, and gRPC. Each architecture has its own attack surface, and our testers tailor their approach to the specific protocols and frameworks in use.
What is white-box API testing?
White-box API testing is our recommended approach, where testers receive full documentation, sample requests, and authentication credentials. This provides the most thorough coverage and best value, allowing testers to assess every endpoint comprehensively rather than spending time on reconnaissance.
How often should I conduct API penetration testing?
Most organisations test their APIs annually as a minimum, with additional testing after significant changes such as new endpoints, authentication updates, or architectural shifts. Compliance frameworks such as PCI DSS may require more frequent testing depending on your risk profile.
Do you provide retesting after remediation?
Yes. Optional retesting is available to confirm that remediation has been successful and vulnerabilities have been closed. This gives you and your stakeholders confidence that fixes have been implemented effectively.
Is API testing required for PCI DSS compliance?
If your APIs handle, transmit, or store cardholder data, they fall within PCI DSS scope and require regular penetration testing. Our CREST-certified API testing provides the evidence and assurance required to support PCI DSS compliance audits.