Refitter: C# source injection through OpenAPI content-type map keys

Summary

Refitter is a tool for generating a C# REST API client using the Refit library. Prior to 2.1.2, content-type keys in the content maps of `requestBody/responses` are emitted verbatim into a Refit `[Headers("Accept: <ct>", "Content-Type: <ct>")]` attribute string without escaping quotation marks. A crafted content-type key in an attacker-influenced OpenAPI description survives default validation without `--skip-validation`, breaks out of the attribute string and enclosing interface and namespace, and can introduce a top-level file class while leaving valid generated C#. A `[ModuleInitializer]` method in that class executes attacker code when the generated assembly is loaded at application startup, without requiring a call to the client. The behavior was verified with Refitter 2.0.0 and .NET 8. This issue is fixed in version 2.1.2.

Remediation

1. Inventory every christianhelle refitter deployment, including staging.
2. No fixed version appears in the public sources yet. Check the references below and the vendor directly.

References

• Referencehttps://github.com/christianhelle/refitter/security/advisories/GHSA-p32v-8v8j-j534
• Referencehttps://github.com/christianhelle/refitter/pull/1178
• Referencehttps://github.com/christianhelle/refitter/commit/ab4d8e439d6f0ee82ad49ee15323978d70fe5a67
• Referencehttps://github.com/christianhelle/refitter/releases/tag/2.1.2
• Referencehttps://github.com/user-attachments/files/29394848/reproduce.sh
• Referencehttps://github.com/user-attachments/files/29394851/maintainer-report.txt
• Referencehttps://github.com/user-attachments/files/29394853/make_spec.py