CVE-2026-59866

CRITICALPre-NVD 9.39.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This critical-severity CVE scores 9.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 1.4% (72nd percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
9.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1.4%CVSS: 9.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
9.3CRITICALmedium confidence
EG Risk
57
EG Risk 57/100

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 (value × EchelonGraph’s weight)
Severity93% × 45%
The EG Score, 9.3 of 10.
Exploitation1.4% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
1.4%
EPSS %ILE
72nd
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

July 16, 2026

Last Modified

August 17, 2026

Advisory Details (4)

Auto-updated Oct 7, 2026
Patch available. Sources: github_commit, github_pr, github_release, github.
GitHub advisoryMentions a patch (unverified)

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 pull request

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 rangeFix by version rangeDependents
Microsoft.OpenApi.Kiota0.1.0-preview ... 1.9.1 (66 versions)
  • 1.30.0 up to 1.32.5: fixed in 1.32.5
  • every version up to 1.29.1: fixed in 1.29.1
—
Microsoft.OpenApi.Kiota.Builder0.2.0-preview ... 1.9.1 (46 versions)
  • 1.30.0 up to 1.32.5: fixed in 1.32.5
  • every version up to 1.29.1: fixed in 1.29.1
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 39× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 148 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 48 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-16 16:43 UTCEPSS rescoreEPSS 1.4% · 72nd percentile
  2. 2026-10-16 07:41 UTCEG score recompute
  3. 2026-10-15 16:32 UTCEPSS rescoreEPSS 1.4% · 72nd percentile
  4. 2026-10-15 06:14 UTCEG score recompute
  5. 2026-10-14 16:33 UTCEPSS rescoreEPSS 1.4% · 72nd percentile
  6. 2026-10-14 01:51 UTCEG score recompute
  7. 2026-10-13 16:34 UTCEPSS rescoreEPSS 1.4% · 72nd percentile
  8. 2026-10-12 22:06 UTCEG score recompute
  9. 2026-10-12 16:34 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  10. 2026-10-12 15:52 UTCEG score recompute
  11. 2026-10-11 19:36 UTCEG score recompute
  12. 2026-10-11 16:51 UTCEG score recompute
  13. 2026-10-11 14:13 UTCEG score recompute
  14. 2026-10-11 13:49 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  15. 2026-10-10 20:00 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  16. 2026-10-09 20:07 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  17. 2026-10-08 17:13 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  18. 2026-10-07 23:48 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  19. 2026-10-06 15:18 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  20. 2026-10-05 17:43 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  21. 2026-10-04 23:22 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  22. 2026-10-03 14:26 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  23. 2026-10-02 17:56 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  24. 2026-10-01 19:50 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  25. 2026-10-01 11:23 UTCEG score recompute
Show 75 more
  1. 2026-09-30 15:03 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  2. 2026-09-29 15:22 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  3. 2026-09-28 13:51 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  4. 2026-09-28 08:36 UTCEG score recompute
  5. 2026-09-27 13:48 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  6. 2026-09-26 15:59 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  7. 2026-09-24 14:04 UTCEPSS rescoreEPSS 1.4% · 71st percentile
  8. 2026-09-24 08:31 UTCEG score recompute
  9. 2026-09-23 17:54 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  10. 2026-09-23 03:02 UTCEG score recompute
  11. 2026-09-20 20:16 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  12. 2026-09-18 19:28 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  13. 2026-09-18 04:39 UTCEG score recompute
  14. 2026-09-17 19:31 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  15. 2026-09-16 14:08 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  16. 2026-09-16 05:15 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  17. 2026-09-15 03:11 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  18. 2026-09-13 23:09 UTCEG score recompute
  19. 2026-09-13 16:47 UTCEPSS rescoreEPSS 1.4% · 70th percentile
  20. 2026-09-12 16:41 UTCEG score recompute
  21. 2026-09-11 21:41 UTCEG score recompute
  22. 2026-09-11 14:53 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  23. 2026-09-10 09:35 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  24. 2026-09-08 22:01 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  25. 2026-09-08 00:30 UTCEG score recompute
  26. 2026-09-07 16:01 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  27. 2026-09-06 17:41 UTCEG score recompute
  28. 2026-09-06 13:47 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  29. 2026-09-05 20:40 UTCEG score recompute
  30. 2026-09-04 05:07 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  31. 2026-09-02 14:12 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  32. 2026-09-01 13:54 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  33. 2026-09-01 04:40 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  34. 2026-08-30 19:34 UTCEG score recompute
  35. 2026-08-30 19:17 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  36. 2026-08-30 03:35 UTCEG score recompute
  37. 2026-08-30 01:22 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  38. 2026-08-28 21:42 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  39. 2026-08-27 21:27 UTCEG score recompute
  40. 2026-08-27 14:25 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  41. 2026-08-26 22:52 UTCEG score recompute
  42. 2026-08-26 14:46 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  43. 2026-08-25 18:55 UTCEG score recompute
  44. 2026-08-25 13:49 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  45. 2026-08-24 15:10 UTCEG score recompute
  46. 2026-08-24 11:33 UTCEG score recompute
  47. 2026-08-23 01:28 UTCEG score recompute
  48. 2026-08-23 00:19 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  49. 2026-08-22 03:13 UTCEG score recompute
  50. 2026-08-21 23:49 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  51. 2026-08-21 01:31 UTCEG score recompute
  52. 2026-08-20 22:55 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  53. 2026-08-19 23:55 UTCEG score recompute
  54. 2026-08-19 17:04 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  55. 2026-08-18 19:56 UTCEG score recompute
  56. 2026-08-18 13:48 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  57. 2026-08-17 13:52 UTCEG score recompute
  58. 2026-08-17 13:47 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  59. 2026-08-16 16:06 UTCEG score recompute
  60. 2026-08-16 14:56 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  61. 2026-08-16 05:13 UTCEG score recompute
  62. 2026-08-16 02:14 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  63. 2026-08-15 03:48 UTCEG score recompute
  64. 2026-08-15 01:30 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  65. 2026-08-13 22:47 UTCEG score recompute
  66. 2026-08-13 22:00 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  67. 2026-08-12 14:04 UTCEG score recompute
  68. 2026-08-12 13:51 UTCEPSS rescoreEPSS 1.4% · 69th percentile
  69. 2026-08-11 16:14 UTCEG score recompute
  70. 2026-08-11 01:44 UTCEG score recompute
  71. 2026-08-11 00:00 UTCEPSS rescoreEPSS 1.4% · 68th percentile
  72. 2026-08-09 17:02 UTCEG score recompute
  73. 2026-08-09 13:46 UTCEPSS rescoreEPSS 1.4% · 68th percentile
  74. 2026-08-08 19:16 UTCEG score recompute
  75. 2026-08-08 16:37 UTCEPSS rescoreEPSS 1.4% · 68th percentile

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-59866?
CVE-2026-59866 is a critical-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-59866 published?
The CVE record for CVE-2026-59866 was published on July 16, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of August 17, 2026; the record at its source may have been updated since.
Is CVE-2026-59866 actively exploited?
CVE-2026-59866 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.4% probability of exploitation in the next 30 days (72nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-59866?
CVE-2026-59866 has a CVSS base score of 9.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-59866?
A fix for CVE-2026-59866 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-59866 are linked in the Vendor Advisories panel on this page.

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