From 015a1077867e36d72d9566902ef16d7b55727b05 Mon Sep 17 00:00:00 2001
From: khangnghiem <56039341+khangnghiem@users.noreply.github.com>
Date: Mon, 6 Jul 2026 20:02:02 +0000
Subject: [PATCH] =?UTF-8?q?=F0=9F=9B=A1=EF=B8=8F=20Sentinel:=20[HIGH]=20Fi?=
 =?UTF-8?q?x=20XSS=20in=20markdown=20rendering?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
---
 .jules/sentinel.md | 5 +++++
 site/app.js        | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 5e0d967e..a3b40c02 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -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.
+
+## 2026-07-06 - XSS vulnerability in Markdown rendering fallback
+**Vulnerability:** The application was vulnerable to Cross-Site Scripting (XSS) when rendering user-provided Markdown notes due to missing HTML sanitization on the `marked.parse` output. A 'fail open' state could exist if fallback mechanisms returned unsanitized raw HTML.
+**Learning:** When using external parsers like `marked.parse`, their raw output is inherently unsafe and requires sanitization. Furthermore, conditional sanitization (e.g. `window.DOMPurify ? sanitize(...) : fallback(...)`) MUST use a secure fallback mechanism such as regex-based HTML escaping rather than falling back to the raw unsanitized HTML.
+**Prevention:** Always wrap dynamically rendered content with `DOMPurify.sanitize()` using required attribute allowlists. Ensure any fallback logic provides escaped text rather than unsanitized raw data to prevent 'fail open' scenarios.
diff --git a/site/app.js b/site/app.js
index 788bd7e7..03e6993e 100644
--- a/site/app.js
+++ b/site/app.js
@@ -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>`;
       }