{"id":"CVE-2026-59860","aliases":["GHSA-3hrf-2gc2-mx32"],"url":"https://o3.security/vulnerability/CVE-2026-59860","summary":"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.","published":"2026-07-16T14:34:24.549Z","modified":"2026-10-07T07:05:29.901419171Z","cvss":null,"epss":{"score":0.01381,"percentile":0.70805,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"Microsoft.OpenApi.Kiota","fixedVersion":"1.32.3"},{"ecosystem":"NuGet","name":"Microsoft.OpenApi.Kiota.Builder","fixedVersion":"1.32.3"},{"ecosystem":"NuGet","name":"Microsoft.OpenApi.Kiota","fixedVersion":"1.29.1"},{"ecosystem":"NuGet","name":"Microsoft.OpenApi.Kiota.Builder","fixedVersion":"1.29.1"}],"fix":{"url":"https://github.com/microsoft/kiota/commit/ebb632db90aa8e3c20949337d9faa2720d64ca44","label":"microsoft/kiota@ebb632d"},"references":[{"type":"WEB","url":"https://github.com/microsoft/kiota/releases/tag/v1.32.3"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59860.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/microsoft/kiota/commit/ebb632db90aa8e3c20949337d9faa2720d64ca44"},{"type":"FIX","url":"https://github.com/microsoft/kiota/pull/7831"},{"type":"PACKAGE","url":"https://github.com/microsoft/kiota"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-07T07:05:29.901419171Z"}}