Affected: PyPI: json-repair

## Circular JSON Schema `$ref` causes unbounded CPU DoS in `json_repair`

### Summary

`SchemaRepairer.resolve_schema()` in `json_repair` follows JSON Schema `$ref` pointers in an unbounded `while` loop without any cycle detection. An attacker who can supply a schema containing a self-referencing `$ref` (e.g., via the demo Flask API or any application that passes untrusted input to `loads(..., schema=...)`), can cause a worker process to spin indefinitely on CPU, resulting in a complete denial of service. No authentication is required against the public demo API. The vulnerability is confirmed reproducible at CVSS 7.5 (High).

### Details

`SchemaRepairer.resolve_schema()` at `src/json_repair/schema_repair.py:184–190` resolves `$ref` chains using a plain `while` loop:

```python # src/json_repair/schema_repair.py:184-190 schema_dict = cast("dict[str, Any]", schema) while "$ref" in schema_dict: ref = schema_dict["$ref"] resolved = self._resolve_ref(ref) if isinstance(resolved, bool): return resolved schema_dict = resolved ```

`_resolve_ref()` at `src/json_repair/schema_repair.py:654–665` always resolves references relative to `self.root_schema`, which is initialised from the caller-supplied schema (`src/json_repair/schema_repair.py:130`). When the schema contains a circular reference such as:

```json {"$ref": "#/definitions/a", "definitions": {"a": {"$ref": "#/definitions/a"}}} ```

`_resolve_ref()` returns the same `dict` object on every iteration,…