🛡️ Sentinel: [HIGH] Fix XSS in upload.js

Added an `_escapeHtml` function to properly sanitize `file.name` before it is dynamically rendered into the DOM using `row.innerHTML`. This mitigates a DOM-based Cross-Site Scripting (XSS) vulnerability.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

.jules/sentinel.md

@@ -28,3 +28,7 @@
 **Vulnerability:** The `/process-url` endpoint used `httpx.AsyncClient(follow_redirects=True)` after validating the initial user-provided URL against SSRF protections. However, it did not validate the target URLs of any subsequent HTTP redirects, allowing an attacker to provide a safe URL that redirects to an internal/private IP, bypassing the security check.
 **Learning:** Initial URL validation is insufficient when the HTTP client is configured to follow redirects automatically. The client must be explicitly configured to validate every redirect target.
 **Prevention:** When using `httpx.AsyncClient(follow_redirects=True)` for user-provided URLs, always implement a redirect validator hook function (e.g., using `event_hooks={'response': [validate_redirect]}`) that resolves the `Location` header and passes it through the same SSRF validation logic before the redirect is followed.
+## 2026-05-27 - DOM-based XSS in upload.js
+**Vulnerability:** The `upload.js` frontend file directly injected the user-controlled `file.name` into a string literal passed to `row.innerHTML`. This allowed a malicious filename (e.g., `<script>alert(1)</script>`) to execute arbitrary JavaScript in the victim's browser context (DOM-based XSS).
+**Learning:** Even internal or local files uploaded by a user can contain malicious filenames. Any data dynamically interpolated into an HTML string that is subsequently rendered via `innerHTML` must be strictly sanitized.
+**Prevention:** Implement and apply an HTML escaping function (e.g., `_escapeHtml`) to replace dangerous characters (`&`, `<`, `>`, `"`, `'`) with their corresponding HTML entities before injecting user-controlled data into the DOM.

frontend/static/js/upload.js

@@ -293,13 +293,25 @@ function processFiles(files, progressContainer, statusMessage) {
     updateStatus();
   }
 
+  function _escapeHtml(unsafe) {
+    if (!unsafe) return '';
+    return String(unsafe)
+      .replace(/&/g, "&")
+      .replace(/</g, "&lt;")
+      .replace(/>/g, "&gt;")
+      .replace(/"/g, "&quot;")
+      .replace(/'/g, "&#039;");
+  }
+
   // Pre-create one progress row per file.
   const queueItems = fileArray.map((file) => {
     const row = document.createElement('div');
     row.className = 'flex flex-col mb-2';
+    const safeFileName = _escapeHtml(file.name);
+
     row.innerHTML = `
       <div class="flex justify-between">
-        <span class="text-sm truncate" title="${file.name}">${file.name}</span>
+        <span class="text-sm truncate" title="${safeFileName}">${safeFileName}</span>
         <span class="text-xs text-gray-500">${formatFileSize(file.size)}</span>
       </div>
       <div class="w-full bg-gray-200 h-2 rounded-full mt-1">