Microsoft Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName
CVE-2026-59866GHSA-4vv7-jj25-4gh6
What to do
Vendor fix available. Upgrade each affected package to the fixed version on its release line (microsoft.openapi.kiota 1.32.5, 1.29.1; microsoft.openapi.kiota.builder 1.32.5, 1.29.1), redeploy, then verify what is actually installed.
This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.
Affected packages
NuGet microsoft.openapi.kiota
- Affected
- >= 1.30.0, < 1.32.5< 1.29.1
- Fixed in
- 1.29.1, 1.32.5
NuGet microsoft.openapi.kiota.builder
- Affected
- >= 1.30.0, < 1.32.5< 1.29.1
- Fixed in
- 1.29.1, 1.32.5
Sources
- GitHub Advisory Database and maintainer security advisories on GitHub
GitHub-reviewed advisory GHSA-4vv7-jj25-4gh6 lists affected ranges: NuGet microsoft.openapi.kiota >=1.30.0 =0 =1.30.0 =0 <1.29.1
VerifiedObserved Structured GitHub Advisory Database record (type=reviewed) from the GitHub REST API.
Severity and exploitation
- Exploitation
- No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
- CVSS 4.0
- 7.0 · 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 · score source
- EPSS
- CVE-2026-59866: 1.41% estimated exploitation activity in the next 30 days; percentile 72.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description
As published by the source; long descriptions are shortened.
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…
Dates and revisions
- Published by the source
- Last modified by the source
- Source last checked
- Revision 1 · created ·
Published from ghsa record GHSA-4vv7-jj25-4gh6
Agent brief
Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.
# Patch Next advisory brief: CVE-2026-59866 Advisory: Microsoft Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName IDs: CVE-2026-59866, GHSA-4vv7-jj25-4gh6 Record: https://patchnext.com/advisories/cve-2026-59866 (revision 1, source checked 26 Oct 2026, 17:05 UTC) Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected. Severity: High (CVSS 7.0) Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV. Vendor response: Vendor fix available; fixed versions by package: microsoft.openapi.kiota 1.32.5, 1.29.1; microsoft.openapi.kiota.builder 1.32.5, 1.29.1. A vendor fix does not mean a deployment is fixed. ## Affected components - NuGet microsoft.openapi.kiota: affected >= 1.30.0, < 1.32.5; < 1.29.1; fixed in 1.29.1, 1.32.5 - NuGet microsoft.openapi.kiota.builder: affected >= 1.30.0, < 1.32.5; < 1.29.1; fixed in 1.29.1, 1.32.5 ## Suggested inspection (read-only) - NuGet microsoft.openapi.kiota: check the installed version with your package manager. - NuGet microsoft.openapi.kiota.builder: check the installed version with your package manager. ## Supported action Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version. ## Required regression checks - Run the test suite and a production build. - Exercise the features that depend on microsoft.openapi.kiota, microsoft.openapi.kiota.builder. - Repeat the inspection and confirm that only fixed versions remain installed. ## Rollback considerations - Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward. ## Unresolved questions - Which deployments run an affected version? - Exploitation status can change. Check again before lowering the priority. - Mark the work resolved only after the fixed version is verified in production. ## Sources - Verified: https://github.com/advisories/GHSA-4vv7-jj25-4gh6 (GitHub-reviewed advisory GHSA-4vv7-jj25-4gh6 lists affected ranges: NuGet microsoft.openapi.kiota >=1.30.0 =0 =1.30.0 =0 <1.29.1) Commands are suggestions: review each one before running it.
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