DAST API Testing with OpenAPI
How providing an OpenAPI definition to a dynamic scanner improves API coverage, test accuracy, and endpoint discovery during dynamic security testing.
Primary question: How can an OpenAPI definition improve dynamic API security testing?
Direct answer
An OpenAPI definition provides a dynamic scanner with structured knowledge of API endpoints, parameters, and expected behavior, enabling more targeted and comprehensive API security testing
An OpenAPI definition provides a dynamic scanner with structured knowledge of API endpoints, parameters, and expected behavior. This enables more targeted API security testing than spidering alone, because the scanner knows which endpoints exist, what parameters they accept, and what request formats to use.
Without an OpenAPI definition, a dynamic scanner must discover API endpoints through spidering and fuzzing, which may miss endpoints that are not easily discoverable through navigation, require specific headers, or are only accessible through programmatic calls. An OpenAPI definition can expose documented endpoints and parameters to the scanner.
An OpenAPI definition does not guarantee complete API coverage. The definition may be incomplete, outdated, or not reflect the actual deployed API. Actual coverage depends on definition accuracy, authentication, supported operations, scanner configuration, and executed tests. Undocumented endpoints require additional discovery.
Definitions
OpenAPI definition
A machine-readable specification of an API that describes its endpoints, parameters, request/response formats, and expected behavior. OpenAPI (formerly Swagger) is a widely used standard for API documentation.
Guided scanning
Dynamic analysis that uses an API specification to guide endpoint discovery, parameter testing, and request generation, providing more targeted coverage than spidering alone.
API endpoint
A specific URL path and HTTP method combination that exposes functionality through an API, such as GET /users or POST /orders.
The engineering problem
API endpoints that are not easily discoverable through spidering may be missed by dynamic scanners, leaving gaps in security coverage.
Without structured API knowledge, dynamic scanners may not generate the correct request formats, headers, or parameter combinations needed to test API endpoints effectively.
API security testing requires understanding of both the API specification and the security weaknesses specific to each endpoint type, including injection, authentication, and data validation issues.
Security controls
Each control inspects a different artifact and produces evidence for an engineering decision.
OpenAPI-based discovery
Guided API discovery- Artifact
- OpenAPI definition file.
- Risk
- Missing API endpoints that are not easily discoverable through spidering.
- Output
- DAST findings about API-specific vulnerabilities based on the OpenAPI definition.
Evidence:
Parameter testing
API parameter analysis- Artifact
- API endpoint parameters defined in the OpenAPI specification.
- Risk
- Missing parameter-specific vulnerabilities such as injection, validation, or type issues.
- Output
- DAST findings about parameter weaknesses including injection, validation, and data handling issues.
Evidence:
API security testing
DAST API testing- Artifact
- Running API with OpenAPI-guided test requests.
- Risk
- API-specific weaknesses not identified through general web application testing.
- Output
- DAST findings about API-specific vulnerabilities including injection, authentication, and data exposure issues.
Evidence:
Verification workflow
- Obtain the OpenAPI definition for the API to be tested.
- Configure DAST to use the OpenAPI definition for guided endpoint discovery and testing.
- Run the DAST scan against the running API with the OpenAPI-guided configuration.
- Review DAST findings about API-specific vulnerabilities.
- If the OpenAPI definition is incomplete, supplement with additional testing to discover undocumented endpoints.
- Correlate DAST findings with SAST findings if available.
- Remediate findings and verify through rescan.
DerScanner · Enterprise
Relationship to DerScanner
DerScanner DAST supports providing an OpenAPI definition to guide API endpoint discovery and testing during dynamic analysis.
DerScanner DAST supports targeted results based on a provided OpenAPI definition for guided API endpoint discovery and testing. [derscanner-dast-settings]
Limits of verification
- The OpenAPI definition must be accurate and up to date. An outdated or incomplete definition may lead to incomplete or inaccurate testing.
- DAST coverage still depends on what attack scenarios and input combinations are exercised during the scan, even with an OpenAPI definition.
- Correlation with SAST findings requires a supported mechanism; not all SAST and DAST tools provide correlation functionality.
Related knowledge
Combining SAST and DAST
Why organizations use both SAST and DAST together
Relationship: related-toAuthenticated DAST Testing
Why authentication is important in dynamic analysis
Relationship: related-toDAST for Single-Page Applications
How dynamic scanners explore JavaScript-heavy applications
Relationship: related-toCanonical terms used: OpenAPI-guided DAST; API security testing; Guided scanning; API endpoint discovery.
Evidence and references
- DerScanner dynamic analysis documentationDerScanner DAST is a web-application scanner that detects vulnerabilities and backdoors by providing malformed or random inputs, using the black-box method without requiring source code. When source code is available, dynamic-analysis results can be correlated with static-analysis results for better accuracy and easier prioritization.
derscanner-dast - DerScanner DAST settings documentationDerScanner DAST settings include authorization methods and credentials for authenticated scanning, standard/aggressive/active-attack scan modes, AJAX spider configuration, OpenAPI definition URL, targeted results based on OpenAPI, and scheduled automatic scanning.
derscanner-dast-settings
DAST API testing with OpenAPI