CVE-2026-59861 — Vulnerability in Microsoft.OpenAPI.Kiota.Builder...

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}, #$var, and #@var within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary Ruby code into generated model classes. # Who is impacted Developers using Kiota to generate Ruby API clients from external or untrusted OpenAPI specifications Teams with CI/CD pipelines configured to automatically regenerate client code from remote specs Applications that deploy generated Ruby code to production servers # Vulnerability details Affected component: CodeMethodWriter.cs Root cause: The shared SanitizeForQuotedLiteral() function in Writers/StringExtensions.cs does not escape the # character # Attack vectors OpenAPI default fields in schema properties Property wire-name hash keys in deserializer/serializer methods Any schema-derived string embedded in Ruby double-quoted literals Severity: Critical when generated code reaches production; High for CI/CD environments with access to production secrets; Medium for public third-party specs; Low for developer-controlled specs. # Patches https://github.com/microsoft/kiota/pull/7746 # Workarounds If you cannot upgrade immediately: 1. Audit and sanitize OpenAPI specifications: Review all OpenAPI specification files for any default values or property names containing the # character. Remove or replace any suspicious strings before code generation. 1. Code review of generated files: Implement mandatory code review of all generated Ruby files before merging into any branch. Look for double-quoted strings containing #{, #$, or #@ patterns. 1. 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. 1. Isolate generated code from production: Do not deploy generated Ruby models to production environments unless the specification source has been verified and reviewed. 1. 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 1.29.1, 1.32.0, or later. Regenerate/refresh existing generated clients as a precaution: ```shell kiota update ``` Refreshing generated clients ensures previously generated vulnerable code is replaced with hardened output.