diff --git a/hermes_cli/session_export_html.py b/hermes_cli/session_export_html.py
index 6b3821ed03e8c..b35a70907f84c 100644
--- a/hermes_cli/session_export_html.py
+++ b/hermes_cli/session_export_html.py
@@ -682,8 +682,16 @@ def _generate_messages_html(messages: List[Dict[str, Any]]) -> str:
                     content_parts.append(str(part))
             content = "\n".join(content_parts)
 
-        # Build message HTML
-        msg_class = f"message message-{role} active"
+        # Build message HTML. The role feeds two sinks and for tool/MCP messages
+        # is externally influenced, so treat each sink on its own terms:
+        #  - display text: HTML-escape (prevents markup/JS injection).
+        #  - class attribute: reduce to a single safe CSS token (alnum/-/_),
+        #    so a crafted role can neither break out of the attribute nor split
+        #    into several unintended classes. Real roles (user/assistant/system/
+        #    tool) are unchanged, so the `.message-<role>` rules still match.
+        safe_role = _escape_html(role)
+        role_class = "".join(c if c.isalnum() or c in "-_" else "-" for c in str(role).lower())
+        msg_class = f"message message-{role_class} active"
         # Delay animation for initial items
         delay_style = f' style="animation-delay: {min(i * 0.05, 1.0)}s"' if i < 10 else ""
         
@@ -691,7 +699,7 @@ def _generate_messages_html(messages: List[Dict[str, Any]]) -> str:
         
         html = f'<div class="{msg_class}"{delay_style}>'
         html += f'  <div class="message-header">'
-        html += f'    <div class="role-badge">{chevron_html} {role_icon} {role}</div>'
+        html += f'    <div class="role-badge">{chevron_html} {role_icon} {safe_role}</div>'
         html += f'    <div class="timestamp">{timestamp}</div>'
         html += '  </div>'
         html += '  <div class="message-body">'
@@ -706,7 +714,7 @@ def _generate_messages_html(messages: List[Dict[str, Any]]) -> str:
                 <div class="tool-call">
                     <div class="tool-call-header">
                         {ICON_CHEVRON_RIGHT.replace('class="', 'class="chevron ')}
-                        {ICON_WRENCH} Tool Call: {fn_name}
+                        {ICON_WRENCH} Tool Call: {_escape_html(fn_name)}
                     </div>
                     <div class="tool-call-content">
                         <pre><code>{_escape_html(args)}</code></pre>
diff --git a/tests/hermes_cli/test_session_export_html_escape.py b/tests/hermes_cli/test_session_export_html_escape.py
new file mode 100644
index 0000000000000..8de3c61b23d8f
--- /dev/null
+++ b/tests/hermes_cli/test_session_export_html_escape.py
@@ -0,0 +1,56 @@
+import re
+
+from hermes_cli.session_export_html import _generate_messages_html
+
+
+def test_tool_call_name_is_escaped_in_html_export():
+    messages = [
+        {
+            "role": "assistant",
+            "content": "",
+            "timestamp": 1700000000,
+            "tool_calls": [
+                {
+                    "function": {
+                        "name": "<script>alert(1)</script>",
+                        "arguments": "{}",
+                    }
+                }
+            ],
+        }
+    ]
+
+    html = _generate_messages_html(messages)
+
+    # Raw, executable markup must never reach the standalone artifact.
+    assert "<script>alert(1)</script>" not in html
+    # The escaped form must be present instead.
+    assert "&lt;script&gt;alert(1)&lt;/script&gt;" in html
+
+
+def test_role_is_escaped_in_html_export():
+    messages = [
+        {
+            "role": "<img src=x onerror=alert(document.domain)>",
+            "content": "hello",
+            "timestamp": 1700000000,
+        }
+    ]
+
+    html = _generate_messages_html(messages)
+
+    assert "<img src=x onerror=alert(document.domain)>" not in html
+    assert "&lt;img src=x onerror=alert(document.domain)&gt;" in html
+    # The class attribute must remain a single, well-formed token: a crafted
+    # role must not break out of it nor split into several unintended classes.
+    class_value = re.search(r'class="(message message-[^"]*active)"', html)
+    assert class_value is not None
+    assert " message-" in class_value.group(1)  # exactly one message-<role> class
+    assert class_value.group(1).count("message-") == 1
+
+
+def test_known_role_keeps_its_css_class():
+    html = _generate_messages_html(
+        [{"role": "assistant", "content": "hi", "timestamp": 1700000000}]
+    )
+    assert 'class="message message-assistant active"' in html