CVE-2026-59860: Kiota: Malicious Code Injection through XML Comments

### 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.