django CMS is an easy-to-use and developer-friendly enterprise content management system powered by Django. From 5.0.8 until 5.0.9, ContentRenderer.render_placeholder in cms/plugin_rendering.py can pass stored, attacker-controlled values to ContentRenderer.render_exception when plugin rendering fails in edit mode. Values from get_short_description(), the exception message, the placeholder, or placeholder.source are interpolated into a cms-rendering-exception heading and later returned through mark_safe. Because the heading is not escaped, stored HTML executes in an editor’s browser, and settings.DEBUG does not prevent the custom heading from rendering. The fix uses format_html to escape the message before safe placeholder output is returned. This issue is fixed in versions 5.0.9.

Affected: PyPI: django-cms

## Summary

When plugin rendering fails in edit mode, django CMS renders a `cms-rendering-exception` block so editors can see that a placeholder could not be rendered. Older code built that block's heading by interpolating the exception message, placeholder/source strings, and the failing plugin's short description directly into an HTML string, then returned the placeholder output as safe markup.

If an editor could store HTML in data used by a plugin's `get_short_description()` (or in other values interpolated into the exception message), and that plugin later raised during edit-mode rendering, the payload was parsed as HTML in the staff user's browser. This is a stored XSS condition in the CMS editing context.

## Impact

The vulnerable path is only reached when placeholder rendering catches a plugin rendering exception:

```python try: placeholder_content = "".join(plugin_content) except Exception as e: context["exc_info"] = sys.exc_info() placeholder_content = self.render_exception("rendering placeholder", context, placeholder, editable) ```

`render_exception()` constructs a `message` from values that can include stored content:

- `value` - the exception message. - `placeholder` - the placeholder string representation. - `placeholder.source` - the source object string representation, such as page content. - `instance.get_short_description()` - plugin-provided summary text, often derived from plugin model fields.

In the vulnerable implementation, that messa…

Affected: PyPI: django-cms

## Summary

When plugin rendering fails in edit mode, django CMS renders a `cms-rendering-exception` block so editors can see that a placeholder could not be rendered. Older code built that block's heading by interpolating the exception message, placeholder/source strings, and the failing plugin's short description directly into an HTML string, then returned the placeholder output as safe markup.

If an editor could store HTML in data used by a plugin's `get_short_description()` (or in other values interpolated into the exception message), and that plugin later raised during edit-mode rendering, the payload was parsed as HTML in the staff user's browser. This is a stored XSS condition in the CMS editing context.

## Impact

The vulnerable path is only reached when placeholder rendering catches a plugin rendering exception:

```python try: placeholder_content = "".join(plugin_content) except Exception as e: context["exc_info"] = sys.exc_info() placeholder_content = self.render_exception("rendering placeholder", context, placeholder, editable) ```

`render_exception()` constructs a `message` from values that can include stored content:

- `value` - the exception message. - `placeholder` - the placeholder string representation. - `placeholder.source` - the source object string representation, such as page content. - `instance.get_short_description()` - plugin-provided summary text, often derived from plugin model fields.

In the vulnerable implementation, that messa…