{"id":"GHSA-h667-4jj2-cgv4","summary":"fastapi-code-generator: Call-time RCE via operation summary -\u003e unescaped route-handler docstring","details":"### Summary\n\nfastapi-code-generator (koxudaxi) emits an operation's `summary` as the generated route handler's docstring, using a triple-quoted string without escaping `\"\"\"`. A `\"\"\"` in the summary closes the docstring and, via concatenation, injects a live expression that becomes an expression statement in the handler body -- which runs when the route handler is CALLED (the endpoint is hit). The summary is a pure data field. Verified on fastapi-code-generator 0.8.0 / Python 3 / FastAPI.\n\n### Details\n\n```python\ndef get_thing() -\u003e None:\n (\n \"\"\"\n x\"\"\"\n + (__import__(\"os\").system('…') or \"\")\n + \"\"\"y\n \"\"\"\n )\n pass\n```\n\nThe generator post-processes with black/isort, so a syntax-breaking payload aborts generation; a valid-Python breakout (`\"\"\"+expr+\"\"\"`, kept valid with `(… or \"\")`) is written and executes at call time. info.description, tags, parameter defaults are escaped; operation description is not emitted into the function body; the summary in the handler docstring is the unescaped sink. Models come from datamodel-code-generator (repr-escaped, no RCE).\n\nNot a duplicate: distinct product from OpenAPI Generator's python-fastapi; and distinct field/sink from the route path -\u003e @app.get('…') decorator (import-time) in the same product -- this is the operation summary in the handler docstring (call-time).\n\n### PoC\n\n`reproduce.sh` (+ `make_spec.py`) attached: generates the app and calls the route handler; the injected expression runs and writes a marker. Verified on 0.8.0.\n\n### Impact\n\nCode execution on the server when the affected endpoint is invoked, in any app generated with fastapi-code-generator from an attacker-controlled or attacker-influenced spec.\n\n### Suggested fix\n\nEscape the summary for the docstring context (escape `\"\"\"`/backslashes via repr, or strip triple-quotes) before emitting it as the handler docstring; apply the same to any free-text field rendered into a docstring. [maintainer-report.txt](https://github.com/user-attachments/files/29534450/maintainer-report.txt) [make_spec.py](https://github.com/user-attachments/files/29534452/make_spec.py)\n[reproduce.sh](https://github.com/user-attachments/files/29534453/reproduce.sh)","aliases":["CVE-2026-63470"],"modified":"2026-11-09T19:15:11.515980431Z","published":"2026-11-09T18:50:00Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-11-09T18:50:00Z","nvd_published_at":"2026-11-03T20:18:15Z","cwe_ids":["CWE-116","CWE-94"],"severity":"CRITICAL"},"references":[{"type":"WEB","url":"https://github.com/koxudaxi/fastapi-code-generator/security/advisories/GHSA-h667-4jj2-cgv4"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63470"},{"type":"WEB","url":"https://github.com/koxudaxi/fastapi-code-generator/commit/49301dbdb82170d7f50877419d994b05cb1fa2bc"},{"type":"WEB","url":"https://github.com/koxudaxi/fastapi-code-generator/commit/b3b9bd66e0b0c4d8c686fda700258104615a1332"},{"type":"PACKAGE","url":"https://github.com/koxudaxi/fastapi-code-generator"},{"type":"WEB","url":"https://github.com/koxudaxi/fastapi-code-generator/releases/tag/0.8.1"}],"affected":[{"package":{"name":"fastapi-code-generator","ecosystem":"PyPI","purl":"pkg:pypi/fastapi-code-generator"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.8.1"}]}],"versions":["0.0.1","0.0.10","0.0.11","0.0.12","0.0.13","0.0.14","0.0.15","0.0.16","0.0.17","0.0.18","0.0.19","0.0.2","0.0.3","0.0.4","0.0.5","0.0.6","0.0.7","0.0.8","0.0.9","0.1.0","0.1.1","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","0.2.5","0.2.6","0.2.7","0.3.0","0.3.1","0.3.2","0.3.3","0.3.4","0.3.5","0.3.6","0.4.0","0.4.1","0.4.2","0.4.3","0.4.4","0.5.0","0.5.1","0.5.2","0.5.3","0.5.3rc0","0.5.4","0.6.0","0.7.0","0.8.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/11/GHSA-h667-4jj2-cgv4/GHSA-h667-4jj2-cgv4.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V4","score":"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"}]}