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

Status: published. Published: 2026-10-30. Updated: 2026-11-02.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- christianhelle / refitter: < 2.1.2 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 8.6 (high); 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; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: 0.35% as of 2026-11-02; percentile 28.69%

- SSVC: exploitation poc; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-94, CWE-116

## Exploit evidence

- exploit: https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8 (ADP: CISA-ADP)

## References

- https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/christianhelle/refitter/pull/1178 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/christianhelle/refitter/commit/63a19b03699a9c267d6fab5f758ec26484db83a1 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/christianhelle/refitter/releases/tag/2.1.2 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/user-attachments/files/29395048/maintainer-report.txt (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/user-attachments/files/29395050/make_spec.py (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/user-attachments/files/29395051/reproduce.sh (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/christianhelle/refitter/security/advisories/GHSA-58x9-vjvp-6mx8 (ADP: CISA-ADP; exploit)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-63346; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-63346; retrieved 2026-11-02; source updated Not reported

Revision: b7f02f4632a569a3153ebea727f0f39690cd30a4a2e61c95a6155dfc8c7c8fee

Canonical: https://y2.dev/cve/CVE-2026-63346

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