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CVE-2026-59866 microsoft CVE debrief

CVE-2026-59866 is a critical vulnerability in Kiota, an OpenAPI based HTTP Client code generator. Prior to version 1.32.5, Kiota emitted unsanitized clientClassName and clientNamespaceName values, allowing an attacker to write generated source outside the output directory and inject arbitrary text into class or namespace declarations. This issue can lead to arbitrary code injection and execution if an attacker controls or compromises the OpenAPI description used with Kiota. The vulnerability has a CVSS score of 9.3 and is considered critical. The issue is fixed in version 1.32.5 with the introduction of GenerationConfiguration.SanitizeClientClassName and SanitizeClientNamespaceName. Developers and users of Kiota should be aware of this vulnerability and take immediate action to update to the patched version.

Vendor
microsoft
Product
kiota
CVSS
CRITICAL 9.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-16
Original CVE updated
2026-08-17
Advisory published
2026-07-16
Advisory updated
2026-08-17

Who should care

Developers and users of Kiota, especially those using versions prior to 1.32.5, should be aware of this vulnerability and take immediate action to update to the patched version. This includes reviewing and sanitizing OpenAPI descriptions used with Kiota, implementing additional security measures such as code reviews and monitoring, and ensuring that generated code is properly validated and verified.

Technical summary

The vulnerability exists due to Kiota's failure to sanitize clientClassName and clientNamespaceName values generated from OpenAPI descriptions. This allows an attacker to manipulate these values, potentially leading to arbitrary code injection and execution. The issue is fixed in version 1.32.5 with the introduction of GenerationConfiguration.SanitizeClientClassName and SanitizeClientNamespaceName. The vulnerability has a CVSS score of 9.3 and is considered critical.

Defensive priority

High

Recommended defensive actions

  • Update Kiota to version 1.32.5 or later
  • Review and sanitize OpenAPI descriptions used with Kiota
  • Implement additional security measures, such as code reviews and monitoring
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-16T16:19:15.493Z and has not been modified since then. The NVD entry is currently Deferred. There is limited information available about the vulnerability, and defenders should verify the affected scope and severity with the vendor. The Kiota team has fixed the issue in version 1.32.5, but details about the vulnerability and its impact are not extensively documented.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-59866 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-59866

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-59866 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-59866

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.