CVE-2026-63345 in Refitter
Summary
by MITRE • 10/31/2026
Refitter is a tool for generating a C# REST API client using the Refit library. Prior to 2.1.2, OpenAPI `paths`-object keys are emitted verbatim into Refit route attributes such as `[Get("<path>")]` without escaping quotation marks or restricting characters. An attacker-influenced single-line, slash-prefixed path survives default validation without `--skip-validation` and can close the attribute string, interface, and namespace while introducing a top-level file class and reopening the generated structure to keep valid C#. A `[ModuleInitializer]` method executes attacker code when an application compiles and loads the generated assembly at startup, even without calling the generated client. The enum and default value sinks are escaped and are not the vulnerable path-emission sink. The behavior was verified on Refitter 2.0.0 with .NET 8. This issue is fixed in version 2.1.2.
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Analysis
by VulDB Data Team • 10/31/2026
The vulnerability identified in versions of Refitter prior to 2.1.2 represents a critical code injection flaw rooted in the improper handling of user-supplied input within OpenAPI specification files. Refitter serves as an automated tool for generating C# REST API client libraries using the Refit library, a process that translates declarative service definitions into executable source code. The core technical failure lies in how the generator processes keys from the paths object within an OpenAPI document. Specifically, these path strings are emitted verbatim into Refit route attributes without any sanitization or escaping of special characters such as quotation marks. This lack of input validation allows a malicious actor to craft a single-line, slash-prefixed path that bypasses default validation mechanisms unless the --skip-validation flag is explicitly used during generation.
The operational impact of this flaw is severe because it enables arbitrary code execution through source code injection rather than runtime exploitation alone. By carefully constructing a path string containing escaped quotation marks and structural C# syntax elements, an attacker can close the current attribute string, terminate the interface definition, and even break out of the namespace block entirely. This allows the insertion of top-level file classes that are syntactically valid within the generated C# project structure. The injected code is not merely dormant; it leverages the [ModuleInitializer] attribute to ensure execution upon assembly load. Consequently, when an application compiles against or loads the maliciously generated client library at startup, the attacker's code executes automatically without any need for specific API calls being made by the end user.
This vulnerability aligns with CWE-94 Improper Control of Generation of Code (Code Injection) and maps to MITRE ATT&CK techniques related to Supply Chain Compromise and Pre-Attack activities such as Artifact Creation. The distinction that enum and default value sinks are properly escaped highlights that this is a specific logic error in path handling rather than a systemic failure across all input types. To mitigate this risk, organizations must immediately upgrade Refitter to version 2.1.2 or later where the issue has been resolved. Additionally, developers should enforce strict validation of OpenAPI specifications before feeding them into code generation tools and consider implementing static analysis checks on generated source files in CI/CD pipelines to detect unexpected structural changes or unauthorized method injections prior to deployment.