CVE-2026-59866

Summary

Microsoft Kiota emitted the x-ms-kiota-info extension's clientClassName or clientNamespaceName value

raw, with no identifier or path sanitization, as both the generated client's class/namespace name

and part of the generated output path. When kiota generate is run without -c/--class-name — the

zero-config workflow that x-ms-kiota-info is explicitly designed for (the API provider supplies the names in

the description so consumers don't have to) — an attacker who controls or tampers with the OpenAPI description

could therefore:

• (CWE-22) write the generated source file to a path outside the -o output directory — e.g.

  clientClassName: "/var/www/html/shell"; and

• (CWE-94) inject arbitrary text into the generated class/namespace declaration, corrupting the generated

  client.

Confirmed on Kiota 1.32.4 (the self-contained linux-x64 release binary), i.e. after the earlier

writer-sink hardening — that fix escaped property/enum/default/serialization sinks but never sanitized the

provider-supplied clientClassName / clientNamespaceName.

Details

clientClassName reached two unsanitized sinks (observed in the generated C#; the same raw emission occurred

for Java, Go, TypeScript, Python, and PHP):

## output FILENAME (CWE-22): clientClassName flows into the file path
clientClassName: "/abs/path/PWNED"   ->   /abs/path/PWNED.cs   (written outside -o)
## class declaration (CWE-94): clientClassName flows verbatim into the type declaration
clientClassName: 'Pwn { } public class INJECTED { } public partial class RealClient'
   ->  public partial class Pwn { } public class INJECTED { } public partial class RealClient : ... { }

clientNamespaceName reached the analogous namespace/path sinks.

Impact

A developer or CI host generating a client from an attacker-controlled or compromised OpenAPI description

(without -c) could create/overwrite a generated source file at an attacker-influenced path and emit

attacker-controlled text into the generated client.

This does not reach clean remote code execution: because clientClassName is reused verbatim at multiple

sites (the class name and the constructor name), injected code cannot be made to compile — it breaks the

build. So the code-injection vector is a generation/build-corruption (integrity/DoS), and the high-severity

primitive is the file write. CWE-22 / CWE-94.

Patches

Fixed in 1.29.1 and 1.32.5 (https://github.com/microsoft/kiota/pull/7884). clientClassName and

clientNamespaceName sourced from x-ms-kiota-info are now sanitized before use:

GenerationConfiguration.SanitizeClientClassName strips any character outside [A-Za-z0-9_] and any invalid

leading character (falling back to ApiClient), and SanitizeClientNamespaceName restricts to

[A-Za-z0-9._-], collapses consecutive dots, strips invalid leading characters (falling back to ApiSdk).

This removes path separators, drive/colon, .., quotes, and braces, so the values can no longer influence

the output path or inject into the declaration.

Remediation

Upgrade to Kiota 1.29.1, 1.32.5, or later and regenerate affected clients.