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🛡️ Sentinel: [CRITICAL] Fix XSS vulnerability in markdown rendering #1251

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🛡️ Sentinel: [CRITICAL] Fix XSS vulnerability in markdown rendering #1251

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4 changes: 4 additions & 0 deletions .jules/sentinel.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,3 +14,7 @@
**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.
## 2024-05-18 - Missing DOMPurify Sanitization in Markdown Rendering
**Vulnerability:** In `site/app.js`, the output of `marked.parse` for markdown notes was being rendered directly to `innerHTML` without sanitization. If the markdown contained embedded malicious HTML, it would be executed, leading to a Cross-Site Scripting (XSS) vulnerability.
**Learning:** Even when using a markdown parser like `marked`, the output can still contain unsanitized HTML if the input markdown includes it. `marked` does not sanitize HTML by default. We must use `DOMPurify` to sanitize the rendered markdown before injecting it into the DOM.
**Prevention:** Always sanitize the output of markdown parsers before assigning it to `innerHTML`. Use conditional sanitization like `window.DOMPurify ? window.DOMPurify.sanitize(rendered) : fallback` and make sure the fallback is secure (e.g., safe regex HTML escaping) rather than a raw, fail-open interpolation.
2 changes: 1 addition & 1 deletion site/app.js
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Expand Up @@ -2724,7 +2724,7 @@ function renderSpecsPanel() {

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