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performing-api-fuzzing-with-restler

Fuzz REST APIs with Microsoft RESTler using compiled OpenAPI grammars and security checkers.

4|Updated Apr 28, 2026
Search Tags:#openapi#security testing#api security#fuzzing#stateful testing#restler#api fuzzing
One-click install
npx skills add https://github.com/braydos-h/BreachPilot --skill performing-api-fuzzing-with-restler-braydos-h
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: performing-api-fuzzing-with-restler
Source: https://github.com/braydos-h/BreachPilot/tree/main/skills/performing-api-fuzzing-with-restler
Command: npx skills add https://github.com/braydos-h/BreachPilot --skill performing-api-fuzzing-with-restler-braydos-h

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes scripts (resource) and references (resource) components.

What problem does it solve? Manually testing REST APIs for security flaws misses stateful bugs that only appear through specific sequences of requests, such as use-after-free on deleted resources or cross-tenant data access. This Skill automates stateful API fuzzing with Microsoft RESTler, compiling OpenAPI specifications into fuzzing grammars and surfacing 500 errors, authentication bypasses, and information leakage. ## Core Features & Use Cases - Grammar Compilation: Convert OpenAPI/Swagger v2 or v3 specifications into RESTler fuzzing grammars with custom injection dictionaries for SQLi, XSS, path traversal, and template injection payloads. - Multi-Mode Fuzzing: Run test mode for endpoint reachability smoke tests, fuzz-lean for a single pass with all security checkers, or full fuzz mode for extended campaigns with time budgets. - Bug Analysis: Parse runSummary.json and bug_buckets output to categorize findings like UseAfterFree, NamespaceRule violations, and information leakage with severity ratings. - Use Case: A security team fuzzes 12 microservice APIs in staging before a release, discovering a critical authentication bypass where a deleted user's token still grants API access. ## Quick Start Compile my OpenAPI spec at openapi.yaml into a RESTler grammar and run a fuzz-lean scan against my staging API with a one-hour time budget.

Frequently Asked Questions about performing-api-fuzzing-with-restler

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I fuzz a REST API with RESTler?▼

Compile your OpenAPI specification with 'Restler compile --api_spec spec.yaml' to generate a fuzzing grammar, then run 'Restler fuzz-lean' with the grammar, dictionary, and target host. RESTler automatically infers producer-consumer dependencies between requests and tests stateful sequences.

What is the difference between RESTler test, fuzz-lean, and fuzz modes?▼

Test mode is a smoke test validating that all endpoints are reachable. Fuzz-lean runs one pass through all endpoints with security checkers enabled. Full fuzz mode runs extended fuzzing campaigns for a specified time budget with deeper sequence exploration.

What security bugs does RESTler detect?▼

RESTler's checkers detect use-after-free on deleted resources, cross-tenant namespace violations, resource hierarchy flaws, information leakage in error responses, and malformed dynamic object handling. It also buckets 500 Internal Server Errors indicating unhandled exceptions.

Does RESTler support authenticated API testing?▼

Yes, RESTler supports token-based authentication through a token_refresh_cmd in engine_settings.json that calls a script returning an authorization header. Configure token_refresh_interval so RESTler refreshes expired tokens during long fuzzing runs.

Can I run RESTler against a production API?▼

No, RESTler should not run against production without explicit authorization and monitoring. It aggressively creates and deletes thousands of resources per hour, so use an isolated staging environment and configure garbage collection intervals.

Why does RESTler skip some endpoints in my OpenAPI spec?▼

Endpoints are skipped when RESTler cannot infer producer-consumer dependencies needed to reach them, often due to missing resource IDs from prior responses. Check compilation warnings and the uncovered endpoints list in runSummary.json, then adjust the grammar or dictionary.

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