Code Injection in Microsoft.OpenApi.Kiota (CVE-2026-59859)
Summary
Code injection in Microsoft.OpenApi.Kiota (CVE-2026-59859). Risk of unauthorized operations or information disclosure. Exploitable via description. Mitigation: upgrade to 1.29.1 or later.
Original description
The description as published by the source.
Impact
The Kiota PHP code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI fields (e.g. description, default values, and property names) directly into PHP double-quoted string literals without properly escaping the $ character. Since PHP evaluates string interpolation expressions like "${expr}", "$var", and "{$obj->prop}" within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary PHP code into generated model and request-builder classes.
Who is impacted
Developers using Kiota to generate PHP API clients from external or untrusted OpenAPI specifications
Teams with CI/CD pipelines configured to automatically regenerate client code from remote specs
Applications that deploy generated PHP code to production servers
Vulnerability details
Affected component: StringExtensions.cs
Root cause: The shared SanitizeDoubleQuote() function in Writers/StringExtensions.cs does not escape the $ character. As a result, any schema-derived string emitted as a PHP double-quoted literal preserves $-prefixed interpolation constructs (${...}, $var, {$...}) verbatim, which PHP evaluates at runtime instead of treating as literal text. This is the same class of code-generation literal-injection flaw previously fixed for the Ruby generator (# interpolation), recurring here as a missed variant for PHP's $ interpolation in the sibling sa…
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-2026-59859 has been found in Microsoft.OpenApi.Kiota.
Attackers can target a specific entry point like description 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-2026-59859" on the vendor's site.
CVE-2026-59859 (Microsoft.OpenApi.Kiota) — CWE-94
Attack surface: description / StringExtensions.cs
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.
Arbitrary code execution (CWE-94) exists in Microsoft.OpenApi.Kiota. Attackers reach the vulnerable code path via description.
Check the vendor advisory for the affected versions of Microsoft.OpenApi.Kiota. Attack surface: description / StringExtensions.cs.
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
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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