Fixing Functional Fuzzer Query Parameters With Request Bodies

by Alex Johnson 62 views

Are you encountering issues with functional fuzzer query parameters when using methods with request bodies like PUT, POST, and PATCH? You're not alone! This article dives deep into a bug report concerning this very problem within the Endava/cats project and explores potential solutions and workarounds. We'll break down the issue, discuss reproduction steps, and analyze the observed behavior to provide a comprehensive understanding and guide you toward resolving this challenge.

Understanding the Functional Fuzzer Query Parameter Issue

The core of the problem lies in the way functional fuzzers handle query parameters for HTTP methods that include a request body. Typically, query parameters are appended to the URL, allowing you to pass additional data to the server. However, a bug has been identified where these parameters don't function correctly when the method involves a body, such as in PUT, POST, or PATCH requests. Methods without a body, like GET and DELETE, seem to work as expected, as do path parameters.

This issue might be related to a previously reported problem, highlighting the complexity of functional fuzzer interactions with various HTTP methods. To fully grasp the impact, let's examine a concrete example and the steps to reproduce it.

Reproducing the Bug: A Step-by-Step Guide

To illustrate the bug, consider the following API definition using the OpenAPI specification (formerly Swagger):

paths:
 run:
 parameters:
 - in: query
 name: myparam
 required: true
 type: string
 get:
 responses:
 '200':
 description: Successful response.
 schema:
 $ref: '#/definitions/RunResult'
 post:
 responses:
 '200':
 description: Successful response.
 schema:
 $ref: '#/definitions/RunResult'
 put:
 responses:
 '200':
 description: Successful response.
 schema:
 $ref: '#/definitions/RunResult'
 patch:
 responses:
 '200':
 description: Successful response.
 schema:
 $ref: '#/definitions/RunResult'
 delete:
 responses:
 '200':
 description: Successful response.
 schema:
 $ref: '#/definitions/RunResult'

This API defines a run path that supports various HTTP methods (GET, POST, PUT, PATCH, DELETE). Each method is expected to return a RunResult. Importantly, there's a query parameter myparam defined as required.

Next, we define a functional fuzzer configuration:

run:
 postRun:
 httpMethod: POST
 description: POST
 schemaPath: myValue
 expectedResponseCode:
 - '200'
 putRun:
 httpMethod: PUT
 description: PUT
 schemaPath: myValue
 expectedResponseCode:
 - '200'
 patchRun:
 httpMethod: PATCH
 description: PATCH
 schemaPath: myValue
 expectedResponseCode:
 - '200'
 delRun:
 httpMethod: DELETE
 description: DELETE
 schemaPath: myValue
 expectedResponseCode:
 - '200'
 getRun:
 httpMethod: GET
 description: GET
 schemaPath: myValue
 expectedResponseCode:
 - '200'

This configuration specifies how the functional fuzzer should interact with the run path for each HTTP method. Now, let's run the fuzzer using the following command:

./bin/cats run ./funcFuzzer.yml -c=./swagger.yml -s=http://localhost:3000

This command instructs the cats tool to run the fuzzer with the specified configuration file (funcFuzzer.yml), OpenAPI specification (swagger.yml), and server URL (http://localhost:3000).

By observing the server's logs (e.g., using console.log(req.method, req.url); in your server-side code), you'll notice the following outcome:

DELETE /run?schemaPath=myValue
GET /run?schemaPath=myValue
PATCH /run
POST /run
PUT /run

The logs reveal that the query parameter schemaPath is correctly appended for the GET and DELETE methods. However, for PATCH, POST, and PUT, the query parameter is missing. This confirms the bug: query parameters are not being included in requests with a body.

Workaround: Forcing Query Parameters

A workaround involves using the --queryParams option. This allows you to explicitly specify query parameters. Let's create a query_params.yaml file with the following content:

all:
 schemaPath: allValue
run:
 schemaPath: runPathValue

This file defines query parameters for all paths and specifically for the run path. Now, run the fuzzer with the --queryParams option:

./bin/cats run ./funcFuzzer.yml -c=./swagger.yml -s=http://localhost:3000 --queryParams=./query_params.yaml

Observing the server logs again, we get:

DELETE /run?schemaPath=myValue&schemaPath=runPathValue
GET /run?schemaPath=myValue&schemaPath=runPathValue
PATCH /run?schemaPath=runPathValue
POST /run?schemaPath=runPathValue
PUT /run?schemaPath=runPathValue

This shows that the --queryParams option does add parameters. However, it also introduces a new issue: duplicate parameters for GET and DELETE methods. The schemaPath parameter appears twice, once with the original value (myValue) and once with the value from the query_params.yaml file (runPathValue).

Analyzing the Observed Behavior

The observed behavior highlights several key points:

  • The functional fuzzer has a bug where query parameters are not automatically included in requests for methods with a body (PUT, POST, PATCH).
  • The --queryParams workaround successfully adds query parameters but introduces duplication for methods without a body (GET, DELETE).
  • This makes it challenging to reliably test APIs with query parameters and methods with bodies using the functional fuzzer.

Proposed Solutions and Suggestions

Based on the analysis, here are some suggested solutions:

  1. Support Query Parameters in the Functional Fuzzer: The most direct solution is to fix the bug in the functional fuzzer so that it correctly includes query parameters for all HTTP methods, regardless of whether they have a body.
  2. Improve --queryParams Behavior: The --queryParams option should be refined to avoid duplicating parameters. Instead of adding an additional value, it should set a default value, overriding any existing values if necessary. This would provide a more consistent and predictable way to specify query parameters.

Additional Context and Version Information

This issue has been observed in versions 13.2.0 and 13.4.3 of the cats tool, indicating that it is a persistent bug. Further investigation and a proper fix are needed to ensure the functional fuzzer works as expected.

Conclusion: Addressing the Functional Fuzzer Query Parameter Bug

In conclusion, the bug affecting functional fuzzer query parameters in methods with request bodies presents a significant challenge for API testing. While a workaround exists using the --queryParams option, it introduces its own set of problems with parameter duplication. The ideal solution involves directly addressing the bug within the functional fuzzer and refining the behavior of the --queryParams option. By implementing these improvements, we can ensure more reliable and comprehensive API testing.

For further reading on API testing and fuzzing techniques, consider exploring resources on websites like the OWASP (Open Web Application Security Project), which offers valuable information and best practices in web application security.