Summary
Microsoft Kiota: Code Generation Literal Injection in Kiota Ruby Generator
Code Generation Literal Injection in Kiota Ruby Generator Leads to Arbitrary Code Execution
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.
Workarounds
If you cannot upgrade immediately:
- 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.
- 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 #{, #$, or #@ patterns.
- Restrict specification sources: Only consume OpenAPI specifications from trusted internal sources. Avoid automatic code generation from external or third-party APIs until this patch is applied.
- Isolate generated code from production: Do not deploy generated Ruby models to production environments unless the specification source has been verified and reviewed.
- Manual escaping (temporary): If regeneration is not possible, manually inspect and edit generated files to escape any # characters in string literals (replace # with # in double-quoted strings).
Remediation
Upgrade Kiota to 1.32.0 or later.
Regenerate/refresh existing generated clients as a precaution:
kiota update
Refreshing generated clients ensures previously generated vulnerable code is replaced with hardened output.
Impact
The Kiota Ruby code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI default fields and property names directly into Ruby double-quoted string literals without properly escaping the # character. Since Ruby evaluates string interpolation expressions like #{expr}, #$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.
Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.
CVE-2026-59861 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.32.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-59861? CVE-2026-59861 is a high-severity code injection vulnerability in Microsoft.OpenAPI.Kiota (nuget), affecting versions < 1.32.0. It is fixed in 1.32.0. Untrusted input is evaluated as executable code within the application's runtime environment.
- How severe is CVE-2026-59861? CVE-2026-59861 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-59861?
Microsoft.OpenAPI.Kiota(nuget) (versions < 1.32.0)Microsoft.OpenAPI.Kiota.Builder(nuget) (versions < 1.32.0)
- Is there a fix for CVE-2026-59861? Yes. CVE-2026-59861 is fixed in 1.32.0. Upgrade to this version or later.
- Is CVE-2026-59861 exploitable, and should I be worried? Whether CVE-2026-59861 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59861 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59861?
- Upgrade
Microsoft.OpenAPI.Kiotato 1.32.0 or later - Upgrade
Microsoft.OpenAPI.Kiota.Builderto 1.32.0 or later
- Upgrade