Fix DOM-based XSS in upload.js by sanitizing file.name

This commit resolves a DOM-based Cross-Site Scripting (XSS) vulnerability in `frontend/static/js/upload.js`. Previously, the user-controlled `file.name` was directly interpolated into the DOM using `innerHTML` without any HTML entity escaping. A maliciously crafted filename could lead to script execution.

A local `_escapeHtml` function has been introduced to safely escape characters like `<`, `>`, `&`, `"`, and `'` before rendering.

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.
+## 2026-05-29 - DOM-based XSS in Upload UI
+**Vulnerability:** In `frontend/static/js/upload.js`, user-controlled file names (`file.name`) were directly injected into the DOM via `innerHTML` without sanitization, leading to a potential DOM-based Cross-Site Scripting (XSS) vulnerability.
+**Learning:** Any user-controlled input, including file names, that is dynamically inserted into HTML (specifically via `innerHTML` or similar sinks) must be treated as untrusted and sanitized.
+**Prevention:** Always define and use a local `_escapeHtml` function to sanitize user-controlled strings (replacing `&`, `<`, `>`, `"`, `'`) before interpolating them into HTML strings that will be rendered via `innerHTML`.

frontend/static/js/upload.js

@@ -293,13 +293,24 @@ function processFiles(files, progressContainer, statusMessage) {
     updateStatus();
   }
 
+  function _escapeHtml(str) {
+    if (!str) return '';
+    return String(str)
+      .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 escapedName = _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="${escapedName}">${escapedName}</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">