Path Traversal in Microsoft.OpenApi.Kiota (CVE-2026-59866)
Summary
Path traversal in Microsoft.OpenApi.Kiota (CVE-2026-59866). Risk of unauthorized operations or information disclosure. Exploitable via clientClassName. Mitigation: upgrade to 1.29.1 or later.
Original description
The description as published by the source.
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
-ooutput 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
provider-supplied clientClassName / clientNamespaceName.
Details
clientClassName reached two unsanitized sinks (observed in the generated C#; the same raw emission occurred
for Java, Go, TypeScript, Python, and PHP):
# output FILENAME (CWE-22): clientClassName flows into the file path
clientClassName: "/abs/path/PWNED" -> /abs/path/PWNED.cs (written outside -o)
# class declaration (CWE-94): clientClassName flows verbat…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-59866 has been found in Microsoft.OpenApi.Kiota.
Attackers can target a specific entry point like clientClassName over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Microsoft.OpenApi.Kiota to 1.29.1 or later.
If unsure, ask your IT team or search "Microsoft.OpenApi.Kiota CVE-2026-59866" on the vendor's site.
CVE-2026-59866 (Microsoft.OpenApi.Kiota) — CWE-22
Attack surface: clientClassName / clientNamespaceName / ApiClient / SanitizeClientNamespaceName
Patched: 1.29.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Path traversal (CWE-22) exists in Microsoft.OpenApi.Kiota. Attackers reach the vulnerable code path via clientClassName.
Check the vendor advisory for the affected versions of Microsoft.OpenApi.Kiota. Attack surface: clientClassName / clientNamespaceName / ApiClient / SanitizeClientNamespaceName.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 1.29.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Microsoft.OpenApi.Kiota' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'Microsoft.OpenApi.Kiota' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
Microsoft.OpenApi.Kiotaを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade Microsoft.OpenApi.Kiota to 1.29.1ステージング環境で 1.29.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com