Potential fix for code scanning alert no. 3: DOM text reinterpreted as HTML

[poad]

Potential fix for https://github.com/poad/llm-ts-example/security/code-scanning/3

In general terms, the problem should be fixed by validating and constraining the user-provided string before using it as the src of the <iframe>. The validation should ensure that only well-formed URLs with allowed schemes (e.g., http: and https:) are accepted, and anything else is rejected or results in no navigation. This avoids interpreting arbitrary DOM text as a URL/HTML-like context and blocks vectors such as javascript:alert(1) or malformed URLs.

For this specific code, the least invasive fix is:

• Introduce a small helper that "sanitizes" a URL string: attempts to construct a URL object and confirms that the protocol is one of an allowlist, like http: or https:. If parsing fails or the protocol is not allowed, return undefined.
• Use this helper when setting the iframe src: instead of (src ?? url) || undefined, compute a safeSrc as either the sanitized src prop or the sanitized context url, and pass that to src. If both are invalid, the iframe will have src={undefined}, effectively loading nothing.
• Keep the existing sandbox attribute unchanged.

These changes all live in chat-app/components/ai-elements/web-preview.tsx. We will:

1. Add a sanitizeUrl helper function near the top of the file (where it’s easy to see and reuse).
2. In WebPreviewBody, compute const safeSrc = sanitizeUrl(src ?? url); and use safeSrc || undefined for the iframe src.

No external libraries are strictly required; we can safely use the built-in URL class in modern browsers/Next.js.

Suggested fixes powered by Copilot Autofix. Review carefully before merging.

[amazon-q-developer]

セキュリティ修正のレビュー結果

このPRは、DOM text reinterpretation脆弱性（Code Scanning Alert #3）に対する重要なセキュリティ修正を実装しています。

主な改善点

• sanitizeUrl関数の追加により、iframe srcでの危険なプロトコル（javascript:など）の実行を防止
• URL検証により、HTTPSとHTTPのみを許可する適切な制限を実装

修正が必要な問題

1. サーバーサイドレンダリング対応: window.location.originへの依存を削除し、絶対URLのみを受け入れるように修正
2. プロトコル検証の強化: より厳密な否定的検証ロジックの実装
3. 入力検証の一貫性: URL入力フィールドでも同様の検証を適用することを推奨

セキュリティ修正の方向性は正しいですが、上記の改善により、より堅牢な実装になります。

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[amazon-q-developer]

🛑 セキュリティ脆弱性: sanitizeUrl関数でサーバーサイドレンダリング時にベースURLが未定義になる可能性があります。window.location.originが利用できない場合、相対URLが予期しない動作を引き起こす可能性があります¹。

Suggested change

	const url = new URL(value, typeof window !== 'undefined' ? window.location.origin : undefined);
	const url = new URL(value);

Footnotes

1. CWE-20: Improper Input Validation - https://cwe.mitre.org/data/definitions/20.html ↩

[amazon-q-developer]

プロトコル検証が不完全です。`

Suggested change

	if (url.protocol === 'http:' || url.protocol === 'https:') {
	return url.toString();
	}
	if (url.protocol !== 'http:' && url.protocol !== 'https:') {
	return undefined;
	}