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Fencer Intel
critical 9.3

CVE-2026-59866 json

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

published 4mo ago modified 18d ago also EUVD-2026-44936 , GHSA-4vv7-jj25-4gh6

cvss
9.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.4%
EPSS 1.4% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

Summary

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.

Patch / fix

  • nuget Microsoft.OpenApi.Kiota 1.29.1, 1.32.5
  • nuget Microsoft.OpenApi.Kiota.Builder 1.29.1, 1.32.5
  • microsoft kiota 1.29.1, 1.32.5
  • microsoft microsoft.openapi.kiota 1.29.1, 1.32.5
  • microsoft microsoft.openapi.kiota.builder 1.29.1, 1.32.5

Is CVE-2026-59866 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
3mo ago

Exploit prediction

1.41% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 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
CNA 4.0 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
nuget Microsoft.OpenApi.Kiota
>=1.30.0, <1.32.5
<1.29.1
1.32.5
1.29.1
nuget Microsoft.OpenApi.Kiota.Builder
>=1.30.0, <1.32.5
<1.29.1
1.32.5
1.29.1

Affected products

  • microsoft kiota

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory
  • CWE-94 Improper Control of Generation of Code

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of microsoft/kiota published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.