CVE-2026-63471: fastapi-code-generator: Import-time RCE via route path -> unescaped @app.get('...') decorator

### Summary fastapi-code-generator (koxudaxi) emits the OpenAPI path into the generated main.py route decorator as a single-quoted string literal (`@app.get('/u/<path>/x')`) without escaping the `'`. A `'` in the path closes the decorator string and, via concatenation, injects a live expression that the decorator argument evaluates when main.py is imported (the ASGI server imports it at startup) -- code execution, no request needed. The path is a pure data field. Verified on fastapi-code-generator 0.8.0 / Python 3 / FastAPI. ### Details ```python @app.get('/u/'+(__import__("os").system('…') or "")+'/x', response_model=None) def get_thing() -> None: pass ``` The generator post-processes output with black/isort, so a syntax-breaking payload aborts generation (DoS); a valid-Python concat (`'+expr+'`, kept valid with `(… or "")`) is written and runs at import. info.description (`description='…'`), tags, and parameter defaults are `'`-escaped; the path in @app.get('…') is the unescaped sink. Models come from datamodel-code-generator (repr-escaped, no RCE). Not a duplicate: distinct product from OpenAPI Generator's python-fastapi backend (different codebase/template/decorator); and distinct from the operation-summary docstring sink in the same product. ### PoC `reproduce.sh` (+ `make_spec.py`) attached: generates the app and merely imports main.py; the injected expression runs at decorator evaluation and writes a marker. Verified on 0.8.0. ### Impact Code execution at import/startup in any application/CI that generates a FastAPI app with fastapi-code-generator from an attacker-controlled or attacker-influenced spec and imports/serves it. Estimated Critical, e.g. `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`. ### Suggested fix Escape the path for the Python string literal (escape ', \, newlines via repr) before emitting @app.get('…'), and validate path characters. [maintainer-report.txt](https://github.com/user-attachments/files/29534357/maintainer-report.txt) [make_spec.py](https://github.com/user-attachments/files/29534358/make_spec.py) [reproduce.sh](https://github.com/user-attachments/files/29534359/reproduce.sh)