CVE-2026-73851: Microsoft Kiota Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-p5rm-jg5c-8c77",
  "modified" : "2026-08-17T15:11:54Z",
  "published" : "2026-07-24T16:14:56Z",
  "aliases" : [ "CVE-2026-73851" ],
  "summary" : "Microsoft Kiota: Path traversal in generated plugin manifest static_template.file reference (percent-encoding bypass)",
  "details" : "### Impact\n\nKiota generates AI plugin manifests from an OpenAPI description. When the description contains an `x-ai-capabilities` response semantics `static_template` (or the adaptive-card extension `x-ai-adaptive-card`), the `file` reference is written into the generated manifest's `response_semantics.static_template.file` and is later resolved by the AI host **relative to the plugin package**.\n\nAn attacker who controls or tampers with the OpenAPI description consumed by Kiota can supply a `file` reference that resolves **outside** the manifest package (e.g. `../../../../etc/passwd`, an absolute path, or a `file://` / `http(s)://` URI). When the generated manifest is deployed and consumed by an AI host, this can lead to inclusion or disclosure of files outside the intended package boundary (CWE-22 Path Traversal, CWE-829 Inclusion of Functionality from an Untrusted Control Sphere).\n\nA mitigation shipped in v1.32.5 (`ExtensionResponseSemanticsStaticTemplate.IsSafeFileReference`) rejected literal traversal, rooted paths, drive-qualified paths, and absolute URIs. However, that check inspected the **raw** reference string, so **percent-encoded** payloads bypassed every check and were still emitted verbatim. Examples that were incorrectly accepted as safe:\n\n| Input | Decodes to |\n|-------|-----------|\n| `%2e%2e/card.json` | `../card.json` |\n| `..%2f..%2f..%2f..%2f..%2f..%2fetc%2fpasswd` | `../../../../../../etc/passwd` |\n| `file%3A%2F%2F%2Fetc%2Fpasswd` | `file:///etc/passwd` |\n| `%2e%2e%2f%2e%2e%2f%2e%2e%2fetc%2fpasswd` | `../../../etc/passwd` |\n\nMulti-level (double) encoding such as `%252e%252e%252fcard.json` was also affected. A follow-up review found additional residual bypasses of the same validator: an embedded NUL byte (`%00`) that truncated the path and defeated the parent-directory segment check, encoding nested deeper than the decode budget (which failed open), and Unicode full-width homoglyphs (e.g. `%EF%BC%8E%EF%BC%8E` → `．．`).\n\n### Patches\n\n- The percent-encoding bypass is fixed by decoding the reference (bounded multi-pass) before validation: https://github.com/microsoft/kiota/pull/7910\n- Residual bypasses (NUL / control characters, decode-budget fail-open, Unicode homoglyphs) are fixed by failing closed on residual encoding, rejecting control characters, and NFKC-folding before validation: https://github.com/microsoft/kiota/pull/7913 (tracking issue https://github.com/microsoft/kiota/issues/7912)\n\nUsers should upgrade to the first released `Microsoft.OpenApi.Kiota` version that includes these fixes (the release following 1.33.0).\n\n### Workarounds\n\n- Only generate clients/plugins from trusted OpenAPI descriptions.\n- Review generated plugin manifests before deployment and reject any `response_semantics.static_template.file` value that is not a simple relative path within the `adaptiveCards/` package folder (no `..`, no rooted/absolute paths, no URIs, no percent-encoded separators).\n\n### References\n\n- CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')\n- CWE-829: Inclusion of Functionality from an Untrusted Control Sphere\n- Affected code: `src/Kiota.Builder/OpenApiExtensions/OpenApiAiCapabilitiesExtension.cs` (`IsSafeFileReference`) and enforcement in `src/Kiota.Builder/Plugins/PluginsGenerationService.cs`.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.30.0"
      }, {
        "fixed" : "1.34.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.29.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/security/advisories/GHSA-p5rm-jg5c-8c77"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/issues/7912"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/pull/7910"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/pull/7913"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/commit/430008e9d700b3fe80f206c672415cfbd8e830e7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/commit/de3d18d9fe31ced4ac749728d3a2f94811f59268"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/microsoft/kiota"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/releases/tag/v1.34.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-829" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T16:14:56Z",
    "nvd_published_at" : null
  }
}