RESTler: Automatic Intelligent REST API Fuzzing

MSR-TR-2018-11 |

Published by Microsoft

Cloud services have recently exploded with the advent of powerful cloud-computing platforms such as Amazon Web Services and Microsoft Azure. Today, most cloud services are accessed through REST APIs, and Swagger is arguably the most popular interface-description language for REST APIs. A Swagger specification describes how to access a cloud service through its REST API (e.g., what requests the service can handle and what responses may be expected).

This paper introduces RESTler, the first automatic intelligent REST API security-testing tool. RESTler analyzes a Swagger specification and generates tests that exercise the corresponding cloud service through its REST API. Each test is defined as a sequence of requests and responses. RESTler generates tests intelligently by (1) inferring dependencies among request types declared in the Swagger specification (e.g., inferring that “a request B should not be executed before a request A” because B takes as an input argument a resource-id returned by A) and by (2) analyzing dynamic feedback from responses observed during prior test executions in order to generate new tests (e.g., learning that “a request C after a request sequence A;B is refused by the service” and therefore avoiding this combination in the future). We show that these two techniques are necessary to thoroughly exercise a service under test while pruning the large search space of possible request sequences. We also discuss the application of RESTler to test GitLab, a large popular open-source self-hosted Git service, and the new bugs that were found.

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November 16, 2020

RESTler is the first stateful REST API fuzzing tool for automatically testing cloud services through their REST APIs and finding security and reliability bugs in these services.

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REST API Fuzz Testing

November 16, 2020

This self-hosted service developed for Azure, including its orchestration engine and security tools (including MSR's RESTler), enables developers to embed security tooling into their CI/CD workflows.

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