# CVE-2026-59866: Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName

> Attackers can inject arbitrary code and write files outside the output directory via malicious OpenAPI descriptions in Kiota code generation.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** GHSA-4vv7-jj25-4gh6

## What is CVE-2026-59866?

CVE-2026-59866 is a critical code injection vulnerability in microsoft kiota, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Kiota is an OpenAPI based HTTP Client code generator. Prior to 1.29.1 and 1.32.5, Kiota emitted x-ms-kiota-info clientClassName and clientNamespaceName values without identifier or path sanitization as both generated client class or namespace names and generated output path components when `kiota generate` ran without -c/--class-name, allowing an attacker-controlled or compromised OpenAPI description to write generated source outside the -o output directory and inject arbitrary text into generated class or namespace declarations. This issue is fixed in version 1.29.1 and 1.32.5 by GenerationConfiguration.SanitizeClientClassName and SanitizeClientNamespaceName.

Weakness: CWE-94 (Improper Control of Generation of Code), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-59866?

8 open source packages ship an affected version, including Microsoft.OpenApi.Kiota and Microsoft.OpenApi.Kiota.Builder.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Microsoft.OpenApi.Kiota` | NuGet | All versions | 1.29.1 |
| `Microsoft.OpenApi.Kiota` | NuGet | All versions | 1.29.1 |
| `Microsoft.OpenApi.Kiota` | NuGet | From 1.30.0 | 1.32.5 |
| `Microsoft.OpenApi.Kiota` | NuGet | From 1.30.0 | 1.32.5 |
| `Microsoft.OpenApi.Kiota.Builder` | NuGet | All versions | 1.29.1 |
| `Microsoft.OpenApi.Kiota.Builder` | NuGet | All versions | 1.29.1 |
| `Microsoft.OpenApi.Kiota.Builder` | NuGet | From 1.30.0 | 1.32.5 |
| `Microsoft.OpenApi.Kiota.Builder` | NuGet | From 1.30.0 | 1.32.5 |

## How do I fix CVE-2026-59866?

Upgrade Microsoft.OpenApi.Kiota to a fixed version for your release line: 1.29.1 or 1.32.5.

## Is CVE-2026-59866 being exploited?

There is no known exploitation of CVE-2026-59866 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-59866 and fix it if it is affected.

What it is: CVE-2026-59866 is a critical code injection vulnerability in microsoft kiota, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-59866 in the wild and no public exploit code.

Affected packages and fixed versions:
- Microsoft.OpenApi.Kiota (NuGet): affected all versions; fixed in 1.29.1
- Microsoft.OpenApi.Kiota (NuGet): affected all versions; fixed in 1.29.1
- Microsoft.OpenApi.Kiota (NuGet): affected from 1.30.0; fixed in 1.32.5
- Microsoft.OpenApi.Kiota (NuGet): affected from 1.30.0; fixed in 1.32.5
- Microsoft.OpenApi.Kiota.Builder (NuGet): affected all versions; fixed in 1.29.1
- Microsoft.OpenApi.Kiota.Builder (NuGet): affected all versions; fixed in 1.29.1
- Microsoft.OpenApi.Kiota.Builder (NuGet): affected from 1.30.0; fixed in 1.32.5
- Microsoft.OpenApi.Kiota.Builder (NuGet): affected from 1.30.0; fixed in 1.32.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-59866/ (Markdown: https://insights.sbomify.com/CVE-2026-59866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59866
- OSV: https://osv.dev/vulnerability/CVE-2026-59866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59866/
Summaries are generated and may contain mistakes; the official description above is the record.