Microsoft Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName

### 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.

Source published

24 Jul 2026 16:12:14 UTC

Source modified

17 Aug 2026 15:00:08 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

Publisher rating · HIGH