diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..c26da33
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,6 @@
+# Sentinel's Journal
+
+## 2026-01-06 - Improper DOM Manipulation XSS
+**Vulnerability:** Found multiple instances of `innerHTML` being used with unsanitized user inputs (Node titles, widget values) in `UIManager.ts`.
+**Learning:** This project uses direct DOM manipulation without a framework, making XSS a primary risk. Developers were manually building HTML strings.
+**Prevention:** Introduced `escapeHtml` utility. Any new code using `innerHTML` MUST sanitize inputs. Prefer `textContent` where possible, or use the `escapeHtml` helper.
diff --git a/src/info-panel/UIManager.ts b/src/info-panel/UIManager.ts
index 46c67a4..dbe0af2 100644
--- a/src/info-panel/UIManager.ts
+++ b/src/info-panel/UIManager.ts
@@ -8,6 +8,7 @@
 import { StateManager } from './StateManager';
 import { Icons } from '../shared/icons';
 import { Logger } from '../shared/logger';
+import { escapeHtml } from '../shared/utils';
 import { formatValue, getValueClass, getValueAttributes, formatWidgetValue } from './ValueFormatter';
 import {
     getCheckpointInfo,
@@ -872,11 +873,11 @@ export class UIManager {
         }
 
         this.elements.content.innerHTML = sections.map(section => `
-            <div class="info-section" data-section="${section.id}">
-                <div class="section-header" data-section="${section.id}">
+            <div class="info-section" data-section="${escapeHtml(section.id)}">
+                <div class="section-header" data-section="${escapeHtml(section.id)}">
                     <span class="section-icon">${section.icon}</span>
-                    <span class="section-title">${section.title}</span>
-                    ${section.badge ? `<span class="section-badge">${section.badge}</span>` : ''}
+                    <span class="section-title">${escapeHtml(section.title)}</span>
+                    ${section.badge ? `<span class="section-badge">${escapeHtml(section.badge)}</span>` : ''}
                     ${section.id !== 'node' ? `<span class="expand-icon">${Icons.chevronRight}</span>` : ''}
                 </div>
                 <div class="section-content">
@@ -894,7 +895,7 @@ export class UIManager {
             const rawValue = String(item.value || '');
             const showCopyBtn = !item.clickable && rawValue.length > 3 && typeof item.value === 'string';
             const copyBtnHtml = showCopyBtn ? `
-                <button class="copy-btn" data-copy-value="${rawValue.replace(/"/g, '&quot;')}" title="Copy to clipboard">
+                <button class="copy-btn" data-copy-value="${escapeHtml(rawValue)}" title="Copy to clipboard">
                     <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
                         <rect x="9" y="9" width="13" height="13" rx="2" ry="2"></rect>
                         <path d="M5 15H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h9a2 2 0 0 1 2 2v1"></path>
@@ -902,7 +903,7 @@ export class UIManager {
                 </button>` : '';
             return `
                             <div class="info-row ${clickableClass}" ${clickableAttr} ${nodeIdAttr} style="${item.clickable ? 'cursor: pointer;' : ''}">
-                                <span class="info-label">${item.label}</span>
+                                <span class="info-label">${escapeHtml(item.label)}</span>
                                 <span class="info-value ${valueClass}" ${valueAttributes}>${value}${dropdownIcon}</span>
                                 ${copyBtnHtml}
                             </div>`;
@@ -1126,13 +1127,13 @@ export class UIManager {
                 const execNode = node as NodeExecOrderEntry;
                 item.innerHTML = `
                     <span style="color: var(--info-panel-accent-color, #4ecdc4); font-weight: 600; min-width: 24px;">#${execNode.order}</span>
-                    <span style="flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;">${execNode.title} (#${execNode.id})</span>
-                    <span style="color: #888; font-size: 11px;">${execNode.type}</span>
+                    <span style="flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;">${escapeHtml(execNode.title)} (#${execNode.id})</span>
+                    <span style="color: #888; font-size: 11px;">${escapeHtml(execNode.type)}</span>
                 `;
             } else {
                 item.innerHTML = `
-                    <span style="flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;">${node.title} (#${node.id})</span>
-                    <span style="color: #888; font-size: 11px;">${node.type}</span>
+                    <span style="flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;">${escapeHtml(node.title)} (#${node.id})</span>
+                    <span style="color: #888; font-size: 11px;">${escapeHtml(node.type)}</span>
                 `;
             }
 
diff --git a/src/info-panel/ValueFormatter.ts b/src/info-panel/ValueFormatter.ts
index fde7e11..a74e97e 100644
--- a/src/info-panel/ValueFormatter.ts
+++ b/src/info-panel/ValueFormatter.ts
@@ -5,6 +5,8 @@
  * Extracted from UIManager.ts for better modularity.
  */
 
+import { escapeHtml } from '../shared/utils';
+
 /**
  * Format a value for display in the info panel.
  * @param value - The value to format
@@ -26,11 +28,11 @@ export function formatValue(value: unknown, label?: string): string {
         label.toLowerCase().includes('positive') ||
         label.toLowerCase().includes('negative')
     )) {
-        return str;
+        return escapeHtml(str);
     }
 
     // Show full text for very long values (no truncation)
-    return str;
+    return escapeHtml(str);
 }
 
 /**
@@ -64,7 +66,7 @@ export function getValueAttributes(value: unknown): string {
 
     const str = String(value);
     if (str.length > 500) { // Only for extremely long text
-        return `title="${str.replace(/"/g, '&quot;')}"`;
+        return `title="${escapeHtml(str)}"`;
     }
 
     return '';
diff --git a/src/shared/utils.ts b/src/shared/utils.ts
index 30c1ed7..6c33ede 100644
--- a/src/shared/utils.ts
+++ b/src/shared/utils.ts
@@ -159,3 +159,18 @@ export function createDebugLogger(
         }
     };
 }
+
+/**
+ * Escapes HTML special characters in a string to prevent XSS.
+ * @param str - The string to escape
+ * @returns Escaped string
+ */
+export function escapeHtml(str: string): string {
+    if (!str) return str;
+    return str
+        .replace(/&/g, "&amp;")
+        .replace(/</g, "&lt;")
+        .replace(/>/g, "&gt;")
+        .replace(/"/g, "&quot;")
+        .replace(/'/g, "&#039;");
+}
diff --git a/tests/unit/Security.test.ts b/tests/unit/Security.test.ts
new file mode 100644
index 0000000..ad3f258
--- /dev/null
+++ b/tests/unit/Security.test.ts
@@ -0,0 +1,25 @@
+import { describe, it, expect } from 'vitest';
+import { formatValue } from '../../src/info-panel/ValueFormatter';
+
+describe('Security', () => {
+    describe('formatValue', () => {
+        it('should escape HTML in values to prevent XSS', () => {
+            const maliciousInput = '<script>alert("xss")</script>';
+            const escaped = formatValue(maliciousInput);
+
+            // Assert that the output does NOT contain the raw script tag
+            expect(escaped).not.toContain('<script>');
+
+            // Assert that the output IS escaped
+            expect(escaped).toContain('&lt;script&gt;');
+            expect(escaped).toContain('&lt;/script&gt;');
+        });
+
+        it('should escape quotes', () => {
+            const input = 'Value with "quotes" and \'single quotes\'';
+            const escaped = formatValue(input);
+            expect(escaped).toContain('&quot;quotes&quot;');
+            expect(escaped).toContain('&#039;single quotes&#039;');
+        });
+    });
+});