Microsoft Kiota: XML Doc-Comment Newline Breakout Code Injection

### Summary Kiota 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). When 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. ## Impact and Preconditions This issue is only practically exploitable when: 1. the OpenAPI description used for generation is from an **untrusted source**, or 2. a normally trusted OpenAPI description has been **compromised/tampered with**. The 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. ## Affected Versions - **Affected:** all versions **< 1.29.1**, **>= 1.30.0, < 1.32.3** - **Fixed: 1.29.1, 1.32.3,** and later ## Illustrative Exploit Example ### Example OpenAPI fragment (malicious description) ```yaml openapi: 3.0.1 info: title: Exploit Demo version: 1.0.0 description: |- Legitimate summary text public static class Pwned { static Pwned() { System.Diagnostics.Process.Start("calc.exe"); } } ``` The newline inside `description` (also exploitable via `\r`, U+0085, U+2028, U+2029) terminates the doc-comment line. ### Example generated C# snippet before fix (illustrative) ```csharp /// Legitimate summary text public static class Pwned { static Pwned() { System.Diagnostics.Process.Start("calc.exe"); } } ``` The injected payload escapes the intended `///` comment context and introduces attacker-controlled statements in generated code. > 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. ## Remediation 1. Upgrade Kiota to **1.32.3 or later**. 2. Regenerate/refresh existing generated clients as a precaution: Refreshing 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.

Source published

24 Jul 2026 15:30:47 UTC

Source modified

17 Aug 2026 15:00:08 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · 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

Publisher rating · HIGH