| Full Fuzzer Name | UnderflowMapSizeFieldsFuzzer |
| Log Key | UMSFF |
| Description | Sends JSON objects/maps with fewer properties than the OpenAPI minProperties constraint (minProperties - 1) to verify minimum property count validation. |
| Enabled by default? | Yes (included in ci, crash, and full profiles) |
| Target field types | Object/map fields declaring minProperties > 0 |
| Expected result when fuzzed field is required | 4XX |
| Expected result when fuzzed field is optional | 4XX |
| Expected result when fuzzed value is not matching field pattern | 4XX |
| Fuzzing logic | Replaces each object/map field that declares minProperties > 0 with an object retaining only minProperties - 1 properties ({} when minProperties == 1). |
| Conditions when this fuzzer will be skipped | When a field is not a JSON object/map or does not declare minProperties > 0. |
| HTTP methods that will be skipped | None |
| Reporting | Reports error if the server accepts the underflow object with 2XX or fails with 5XX; reports success when rejected with 4XX. |