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🛡️ Sentinel: [HIGH] Fix XSS vulnerability in markdown rendering #1253

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🛡️ Sentinel: [HIGH] Fix XSS vulnerability in markdown rendering #1253

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5 changes: 5 additions & 0 deletions .jules/sentinel.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,3 +14,8 @@
**Vulnerability:** Several `escapeHtml` implementations used DOM manipulation (`document.createElement('div').innerHTML`) or incomplete string replacement, failing to escape single and double quotes.
**Learning:** Incomplete escaping allows XSS payloads to break out of HTML attributes (e.g., `<input value="${escapeHtml(userInput)}">`).
**Prevention:** Always use `String(text)` cast combined with a comprehensive replace chain for `&`, `<`, `>`, `"`, and `'` (e.g., `&#039;`) in custom string escaping functions.

## 2024-07-08 - XSS in Markdown Rendering
**Vulnerability:** The Markdown rendering logic in `site/app.js` passed unsanitized output from `marked.parse()` directly into `innerHTML`, creating a high-severity XSS vulnerability if a user note contained malicious markdown.
**Learning:** The fallback for DOMPurify must be securely escaped text rather than the raw `rendered` HTML. Reverting to the raw unsanitized HTML on missing dependencies is a strict "fail open" pattern that leaves the app exposed.
**Prevention:** Always implement conditional sanitization that "fails closed" by gracefully degrading to safely escaped text if a sanitization library is unavailable.
6 changes: 5 additions & 1 deletion site/app.js
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Expand Up @@ -2724,7 +2724,11 @@ function renderSpecsPanel() {

if (typeof marked !== 'undefined') {
const rendered = marked.parse(processedNote);
html += rendered;
if (window.DOMPurify) {
html += window.DOMPurify.sanitize(rendered, { ADD_ATTR: ['data-note-node', 'data-node'] });
} else {
html += `<pre>${processedNote.replace(/</g, '&lt;').replace(/>/g, '&gt;')}</pre>`;
}
} else {
html += `<pre>${processedNote.replace(/</g, '&lt;').replace(/>/g, '&gt;')}</pre>`;
}
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