diff --git a/server/routes/widgets.js b/server/routes/widgets.js
index b3f6d9d..c16751a 100644
--- a/server/routes/widgets.js
+++ b/server/routes/widgets.js
@@ -65,6 +65,21 @@ function safeUrl(url) {
   } catch { return 'about:blank'; }
 }
 
+// Security: widget render output is public and CSP-exempt, so config values that
+// get inlined into <style>/CSS must not be able to break out (a config field set
+// via the API could otherwise carry `}</style><script>...`). safeCss allows
+// colors/gradients but rejects breakout/exfil constructs; safeNumber coerces to
+// a finite number (so e.g. font_size can't smuggle markup).
+function safeCss(v, fallback) {
+  if (typeof v !== 'string') return fallback;
+  if (/[<>{}\\;]/.test(v) || /url\s*\(/i.test(v) || /@import/i.test(v) || /expression/i.test(v) || /javascript:/i.test(v)) return fallback;
+  return v.trim().slice(0, 200);
+}
+function safeNumber(v, fallback) {
+  const n = Number(v);
+  return Number.isFinite(n) ? n : fallback;
+}
+
 // List widgets accessible to the caller's current workspace, plus any
 // platform-template rows (workspace_id IS NULL) shared with all workspaces.
 // Phase 2.2d: workspace-scoped. Cross-workspace visibility comes from
@@ -186,9 +201,9 @@ router.post('/preview', (req, res) => {
 function renderClock(c) {
   return `<!DOCTYPE html><html><head><style>
   * { margin:0; padding:0; box-sizing:border-box; }
-  body { background:${c.background || 'transparent'}; display:flex; flex-direction:column; align-items:center; justify-content:center; height:100vh; font-family:-apple-system,sans-serif; overflow:hidden; }
-  #time { font-size:${c.font_size || 64}px; font-weight:700; color:${c.color || '#FFFFFF'}; }
-  #date { font-size:${Math.max(16, (c.font_size || 64) / 3)}px; color:${c.color || '#FFFFFF'}; opacity:0.7; margin-top:8px; }
+  body { background:${safeCss(c.background, 'transparent')}; display:flex; flex-direction:column; align-items:center; justify-content:center; height:100vh; font-family:-apple-system,sans-serif; overflow:hidden; }
+  #time { font-size:${safeNumber(c.font_size, 64)}px; font-weight:700; color:${safeCss(c.color, '#FFFFFF')}; }
+  #date { font-size:${Math.max(16, safeNumber(c.font_size, 64) / 3)}px; color:${safeCss(c.color, '#FFFFFF')}; opacity:0.7; margin-top:8px; }
 </style></head><body>
 <div id="time"></div>
 ${c.show_date !== false ? '<div id="date"></div>' : ''}
@@ -205,9 +220,9 @@ setInterval(update, 1000); update();
 function renderWeather(c) {
   return `<!DOCTYPE html><html><head><style>
   * { margin:0; padding:0; box-sizing:border-box; }
-  body { background:${c.background || 'transparent'}; display:flex; align-items:center; justify-content:center; height:100vh; font-family:-apple-system,sans-serif; color:${c.color || '#FFF'}; }
+  body { background:${safeCss(c.background, 'transparent')}; display:flex; align-items:center; justify-content:center; height:100vh; font-family:-apple-system,sans-serif; color:${safeCss(c.color, '#FFF')}; }
   .weather { text-align:center; }
-  .temp { font-size:${c.font_size || 48}px; font-weight:700; }
+  .temp { font-size:${safeNumber(c.font_size, 48)}px; font-weight:700; }
   .location { font-size:18px; opacity:0.7; margin-top:4px; }
   .desc { font-size:16px; opacity:0.6; margin-top:8px; }
   .icon { font-size:64px; }
@@ -240,9 +255,9 @@ load(); setInterval(load, 600000);
 function renderRSS(c) {
   return `<!DOCTYPE html><html><head><style>
   * { margin:0; padding:0; box-sizing:border-box; }
-  body { background:${c.background || '#000'}; height:100vh; overflow:hidden; font-family:-apple-system,sans-serif; }
-  .ticker { display:flex; align-items:center; height:100%; white-space:nowrap; animation:scroll ${c.scroll_speed || 30}s linear infinite; }
-  .item { display:inline-block; padding:0 40px; font-size:${c.font_size || 24}px; color:${c.color || '#FFF'}; }
+  body { background:${safeCss(c.background, '#000')}; height:100vh; overflow:hidden; font-family:-apple-system,sans-serif; }
+  .ticker { display:flex; align-items:center; height:100%; white-space:nowrap; animation:scroll ${safeNumber(c.scroll_speed, 30)}s linear infinite; }
+  .item { display:inline-block; padding:0 40px; font-size:${safeNumber(c.font_size, 24)}px; color:${safeCss(c.color, '#FFF')}; }
   .item .title { font-weight:600; }
   .item .sep { margin:0 20px; opacity:0.3; }
   @keyframes scroll { 0%{transform:translateX(100vw)} 100%{transform:translateX(-100%)} }
@@ -253,7 +268,7 @@ async function load() {
   try {
     const r = await fetch('https://api.rss2json.com/v1/api.json?rss_url=' + encodeURIComponent('${escapeHtml(c.feed_url) || ''}'));
     const d = await r.json();
-    const items = d.items?.slice(0, ${c.max_items || 10}) || [];
+    const items = d.items?.slice(0, ${safeNumber(c.max_items, 10)}) || [];
     // NOTE: RSS feed titles are external content - using textContent instead of innerHTML to prevent XSS
     document.getElementById('ticker').innerHTML = items.map(i => {
       const el = document.createElement('span'); el.textContent = i.title;
@@ -272,12 +287,21 @@ function renderText(c) {
   html = html.replace(/font-size:\s*([\d.]+)px/g, (match, px) => {
     return `font-size:${(parseFloat(px) / 108).toFixed(2)}vw`;
   });
-  return `<!DOCTYPE html><html><head><style>
+  // Security: c.html / c.css are intentionally raw user-authored content, but the
+  // render is public and same-origin with the dashboard - injected <script> could
+  // otherwise read the dashboard's localStorage JWT. Render the user content inside
+  // a sandboxed iframe with NO allow-same-origin: scripts still run (so legit
+  // widget markup works) but in a null origin that can't touch the app's storage.
+  const inner = `<!DOCTYPE html><html><head><style>
   * { margin:0; padding:0; box-sizing:border-box; }
-  body { background:${c.background || 'transparent'}; width:100vw; height:100vh; overflow:hidden; }
+  html, body { width:100vw; height:100vh; overflow:hidden; }
   ${c.css || ''}
 </style></head><body>${html}</body></html>`;
-  // NOTE: c.html is intentionally rendered as raw HTML - this is user-authored content for the text widget
+  return `<!DOCTYPE html><html><head><style>
+  * { margin:0; padding:0; }
+  html, body { width:100vw; height:100vh; overflow:hidden; background:${safeCss(c.background, 'transparent')}; }
+  iframe { width:100%; height:100%; border:0; display:block; }
+</style></head><body><iframe sandbox="allow-scripts" srcdoc="${escapeHtml(inner)}"></iframe></body></html>`;
 }
 
 function renderWebpage(c) {
@@ -294,7 +318,7 @@ ${c.refresh_interval > 0 ? `<script>setInterval(()=>document.querySelector('ifra
 
 function renderSocial(c) {
   return `<!DOCTYPE html><html><head><style>
-  body { background:${c.background || '#000'}; color:${c.color || '#FFF'}; font-family:-apple-system,sans-serif; display:flex; align-items:center; justify-content:center; height:100vh; margin:0; }
+  body { background:${safeCss(c.background, '#000')}; color:${safeCss(c.color, '#FFF')}; font-family:-apple-system,sans-serif; display:flex; align-items:center; justify-content:center; height:100vh; margin:0; }
 </style></head><body>
 <div style="text-align:center">
   <p style="font-size:24px">Social Feed</p>
diff --git a/server/test/widget-render-xss.test.js b/server/test/widget-render-xss.test.js
new file mode 100644
index 0000000..3a3d6b2
--- /dev/null
+++ b/server/test/widget-render-xss.test.js
@@ -0,0 +1,61 @@
+'use strict';
+
+// Verifies the public widget render endpoint sanitizes config that gets inlined
+// into <style>/CSS (clock/weather/rss/social) and isolates the text widget's
+// raw HTML in a sandboxed, null-origin iframe.
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const Database = require('better-sqlite3');
+
+process.env.JWT_SECRET = 'test-secret-widget-xss';
+
+const db = new Database(':memory:');
+db.exec(`CREATE TABLE widgets (id TEXT PRIMARY KEY, widget_type TEXT, config TEXT, workspace_id TEXT);`);
+const dbModulePath = require.resolve('../db/database');
+require.cache[dbModulePath] = { id: dbModulePath, filename: dbModulePath, loaded: true, exports: { db } };
+
+const express = require('express');
+const widgetsRouter = require('../routes/widgets');
+const app = express();
+app.use('/api/widgets', widgetsRouter);
+const server = app.listen(0);
+let base;
+test.before(async () => { await new Promise(r => server.listening ? r() : server.once('listening', r)); base = `http://127.0.0.1:${server.address().port}`; });
+test.after(() => { server.close(); db.close(); });
+
+const seed = (id, type, config) => db.prepare('INSERT INTO widgets (id, widget_type, config, workspace_id) VALUES (?,?,?,?)').run(id, type, JSON.stringify(config), 'ws1');
+const render = async (id) => (await fetch(`${base}/api/widgets/${id}/render`)).text();
+
+const CSS_BREAKOUT = 'red}</style><script>document.title="pwned"</script><style>{';
+
+test('clock widget: malicious background/color/font_size cannot break out of <style>', async () => {
+  seed('clock1', 'clock', { background: CSS_BREAKOUT, color: CSS_BREAKOUT, font_size: '64px}</style><script>x</script>' });
+  const html = await render('clock1');
+  assert.ok(!html.includes('</style><script>document.title'), 'CSS breakout payload must be rejected');
+  assert.ok(html.includes('background:transparent'), 'invalid background falls back to default');
+  assert.ok(/font-size:64px/.test(html), 'invalid font_size falls back to numeric default');
+});
+
+test('rss widget: scroll_speed/max_items coerced to numbers (no injection)', async () => {
+  seed('rss1', 'rss', { scroll_speed: '30s}</style><script>y</script>', max_items: '10);evil(' , background: CSS_BREAKOUT });
+  const html = await render('rss1');
+  assert.ok(!html.includes('</style><script>y'), 'scroll_speed cannot inject');
+  assert.ok(!html.includes('evil('), 'max_items cannot inject into the script');
+  assert.ok(html.includes('background:#000'), 'invalid background -> default');
+});
+
+test('text widget: raw HTML is isolated in a null-origin sandboxed iframe', async () => {
+  seed('text1', 'text', { html: '<script>parent.localStorage.token</script>', css: 'body{}' });
+  const html = await render('text1');
+  assert.ok(html.includes('<iframe sandbox="allow-scripts"'), 'user HTML wrapped in sandboxed iframe');
+  assert.ok(!/<body[^>]*>\s*<script>parent\.localStorage/.test(html), 'raw script must not sit in the top-level (same-origin) document');
+  assert.ok(html.includes('&lt;script&gt;parent.localStorage'), 'user script is escaped into srcdoc, runs only in the sandboxed frame');
+});
+
+test('valid color/gradient backgrounds are preserved', async () => {
+  seed('clock2', 'clock', { background: 'linear-gradient(45deg, #ff0000, #00ff00)', color: '#3B82F6' });
+  const html = await render('clock2');
+  assert.ok(html.includes('linear-gradient(45deg, #ff0000, #00ff00)'), 'legit gradient preserved');
+  assert.ok(html.includes('color:#3B82F6'), 'legit hex color preserved');
+});
