CVE-2026-59860: Microsoft Kiota XML Doc-Comment Newline Breakout Code Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3hrf-2gc2-mx32",
  "modified" : "2026-08-17T14:52:01Z",
  "published" : "2026-07-24T15:30:47Z",
  "aliases" : [ "CVE-2026-59860" ],
  "summary" : "Microsoft Kiota: XML Doc-Comment Newline Breakout Code Injection",
  "details" : "### Summary\n\nKiota versions **prior to 1.32.3 and 1.29.1** are affected by a code-generation injection vulnerability in the C# XML documentation-comment sink (the `description`, `externalDocs` label, and `externalDocs` link fields emitted as `/// …` comments).\n\nWhen text from an OpenAPI description is written into single-line XML doc comments without stripping newline and Unicode line-terminator characters, an attacker can break out of the `///` comment line and inject additional code into generated C# clients.\n\n## Impact and Preconditions\n\nThis issue is only practically exploitable when:\n\n1.  the OpenAPI description used for generation is from an **untrusted source**, or\n2.  a normally trusted OpenAPI description has been **compromised/tampered with**.\n\nThe injected code is compiled (and may execute) when the developer or CI **builds** the generated client. If you only generate from trusted, integrity-protected API descriptions, risk is significantly reduced.\n\n## Affected Versions\n\n- **Affected:** all versions **< 1.29.1**, **>= 1.30.0, < 1.32.3**\n- **Fixed: 1.29.1, 1.32.3,** and later\n\n## Illustrative Exploit Example\n\n### Example OpenAPI fragment (malicious description)\n\n```yaml\nopenapi: 3.0.1\ninfo:\n  title: Exploit Demo\n  version: 1.0.0\n  description: |-\n    Legitimate summary text\n    public static class Pwned { static Pwned() { System.Diagnostics.Process.Start(\"calc.exe\"); } }\n```\n\nThe newline inside `description` (also exploitable via `\\r`, U+0085, U+2028, U+2029) terminates the doc-comment line.\n\n### Example generated C# snippet before fix (illustrative)\n\n```csharp\n/// Legitimate summary text\npublic static class Pwned { static Pwned() { System.Diagnostics.Process.Start(\"calc.exe\"); } }\n```\n\nThe injected payload escapes the intended `///` comment context and introduces attacker-controlled statements in generated code.\n\n> Note: this exploit is not limited to the `description` field, but may also impact the `externalDocs` label and link text and other doc-comment-derived locations.\n\n## Remediation\n\n1.  Upgrade Kiota to **1.32.3 or later**.\n2.  Regenerate/refresh existing generated clients as a precaution:\n\nRefreshing generated clients ensures previously generated vulnerable code is replaced with hardened output. The fix (PR microsoft/kiota#7831) strips `\\r`, `\\n`, `\\u0085`, `\\u2028`, `\\u2029` (and normalizes tabs) from description, label, and link text before emitting doc comments.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.30.0"
      }, {
        "fixed" : "1.32.3"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota.Builder"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.30.0"
      }, {
        "fixed" : "1.32.3"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.29.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Microsoft.OpenApi.Kiota.Builder"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.29.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/security/advisories/GHSA-3hrf-2gc2-mx32"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59860"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/pull/7831"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/commit/ebb632db90aa8e3c20949337d9faa2720d64ca44"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/microsoft/kiota"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/kiota/releases/tag/v1.32.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T15:30:47Z",
    "nvd_published_at" : "2026-07-16T15:16:35Z"
  }
}