CVE-2026-59866

CRITICALPre-NVD 9.39.3—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 1.4%, top 30% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
9.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 9.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
9.3
EG Score
9.3(medium)
EG Risk
57(Track)
EG Risk 57/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity93% × 45%
Exploitation1% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
70%
KEV
Not listed

Published

July 16, 2026

Last Modified

August 17, 2026

Advisory Details (4)

Auto-updated Sep 14, 2026
Patch available. Sources: github_commit, github_pr, github_release, github.
github Patch Available

Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName (Microsoft Kiota) · Advisory · microsoft/kiota · GitHub

https://github.com/microsoft/kiota/security/advisories/GHSA-4vv7-jj25-4gh6
github_release Patch Available

v1.32.5

Patch available: microsoft/kiota v1.32.5

https://github.com/microsoft/kiota/releases/tag/v1.32.5
github_pr

fix: sanitizes the client class and namespace names to avoid code injection

Fix merged in microsoft/kiota PR #7884 on 2026-07-01 — awaiting tagged release

https://github.com/microsoft/kiota/pull/7884
github_commit

commit dc812dbbf88e (microsoft/kiota)

Fix landed in microsoft/kiota commit dc812dbbf88e — awaiting tagged release

https://github.com/microsoft/kiota/commit/dc812dbbf88ef7edf53a890d36b2f9d1460e947d

Vendor Advisories for CVE-2026-59866(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(2 across 1 ecosystem)
NuGet(2)
PackageVulnerable rangeFixed inDependents
Microsoft.OpenApi.Kiota0.1.0-preview ... 1.9.1 (66 versions)1.29.1—
Microsoft.OpenApi.Kiota.Builder0.2.0-preview ... 1.9.1 (46 versions)1.29.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 41× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 112 total refreshes for this CVE.

  1. 2026-09-18 19:28 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2026-59866?
CVE-2026-59866 is a critical vulnerability published on July 16, 2026. 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…
When was CVE-2026-59866 disclosed?
CVE-2026-59866 was first published in the National Vulnerability Database on July 16, 2026, with the most recent update on August 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-59866 actively exploited?
CVE-2026-59866 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 29.6% of all scored CVEs.
What is the CVSS score of CVE-2026-59866?
CVE-2026-59866 has a CVSS v3 base score of 9.3 (NVD).
How do I remediate CVE-2026-59866?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-59866, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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