Microsoft Kiota: Code Generation Literal Injection in Kiota Ruby Generator

Code Generation Literal Injection in Kiota Ruby Generator Leads to Arbitrary Code Execution

Impact

The Kiota Ruby code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI default fields and property names directly into Ruby double-quoted string literals without properly escaping the # character. Since Ruby evaluates string interpolation expressions like #{expr}, #$var, and #@var within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary Ruby code into generated model classes.

Who is impacted

Developers using Kiota to generate Ruby API clients from external or untrusted OpenAPI specifications
Teams with CI/CD pipelines configured to automatically regenerate client code from remote specs
Applications that deploy generated Ruby code to production servers

Vulnerability details

Affected component: CodeMethodWriter.cs
Root cause: The shared SanitizeForQuotedLiteral() function in Writers/StringExtensions.cs does not escape the # character

Attack vectors

OpenAPI default fields in schema properties
Property wire-name hash keys in deserializer/serializer methods
Any schema-derived string embedded in Ruby double-quoted literals
Severity: Critical when generated code reaches production; High for CI/CD environments with access to production secrets; Medium for public third-party specs; Low for developer-controlled specs.

Patches

https://github.com/microsoft/kiota/pull/7746

Workarounds

If you cannot upgrade immediately:

1. Audit and sanitize OpenAPI specifications: Review all OpenAPI specification files for any default values or property names containing the # character. Remove or replace any suspicious strings before code generation.
2. Code review of generated files: Implement mandatory code review of all generated Ruby files before merging into any branch. Look for double-quoted strings containing #{, #$, or #@ patterns.
3. Restrict specification sources: Only consume OpenAPI specifications from trusted internal sources. Avoid automatic code generation from external or third-party APIs until this patch is applied.
4. Isolate generated code from production: Do not deploy generated Ruby models to production environments unless the specification source has been verified and reviewed.
5. Manual escaping (temporary): If regeneration is not possible, manually inspect and edit generated files to escape any # characters in string literals (replace # with # in double-quoted strings).

Remediation

Upgrade Kiota to 1.32.0 or later.
Regenerate/refresh existing generated clients as a precaution:

 1kiota update

Refreshing generated clients ensures previously generated vulnerable code is replaced with hardened output.