Black-box fuzzer that fuzzes APIs based on OpenAPI specification. All you need to do is to supply URL of the API and its specification. Find bugs for free!
The fuzzer has been used to find bugs in numerous software. Some of the well-known fuzzed software include[^1]:
The category of bugs differ, but some of the common are parsing bugs, invalid format bugs and querying non-existent entities. If you have found bugs with this fuzzer, please reach out to me. I would love to hear from you. Feel free to submit a PR and add your finding to the list above.
To build the fuzzer, you will need to have rust installed.
```sh
cargo install openapi-fuzzer
git clone git@github.com:matusf/openapi-fuzzer.git cd openapi-fuzzer
cargo install --path .
cargo build ```
After installation you will have two binaries, openapi-fuzzer and openapi-fuzzer-resender. The openapi-fuzzer will fuzz the API according to the specification and report any findings. All findings will be located in a results directory in a JSON format. After you are done with fuzzing, you can use openapi-fuzzer-resender to resend payloads that triggered a bugs and examine the cause in depth.
-i flag. It is adviced to fuzz it two stages. Firstly, run the fuzzer without -i flag for a minute. Then check results folder for the reported findings. If there are reports from status codes you do not care about, add them via -i flag and rerun the fuzzer./v1 or /api, however, the specifications are sometimes writen without it. Do not forget to include the path prefix in the url.-H flag. It may be useful when you would like to increase coverage by providing some sort of authorization.```txt
$ openapi-fuzzer --help
Usage: openapi-fuzzer -s
OpenAPI fuzzer
Options: -s, --spec path to OpenAPI specification -u, --url url of api to fuzz -i, --ignore-status-code status codes that will not be considered as finding -H, --header additional header to send --help display usage information
$ openapi-fuzzer -s spec.yaml -u http://127.0.0.1:8200/v1/ -i 404 ```
When you are done fuzzing you can replay the findings. All findings are stored in the results folder in path according to finding's endpoint and method. To resend the same payload to API, you simply run openapi-fuzzer-resender with path to the finding file as an argument. You can overwrite the headers with -H flag as well, which is useful for example, when the authorization token expired.
```txt $ tree -L 3 results/ results/ ├── sys-leases-renew │ └── POST │ └── 500 └── sys-seal └── POST └── 500
$ openapi-fuzzer-resender --help
Usage: openapi-fuzzer-resender
Resender of openapi-fuzzer results
Options: -H, --header extra header --help display usage information
$ openapi-fuzzer-resender results/sys-seal/POST/500/1b4e8a77.json Response[status: 500, status_text: Internal Server Error, url: http://127.0.0.1:8200/v1/sys/seal] {"errors":["1 error occurred: * missing client token"]} ```