Wagtail Vulnerable to Cross-site Scripting in TableBlock class attributes

Impact

A stored Cross-site Scripting (XSS) vulnerability exists on rendering TableBlock blocks within a StreamField. A user with access to create or edit pages containing TableBlock StreamField blocks is able to set specially-crafted class attributes on the block which run arbitrary JavaScript code when the page is viewed. When viewed by a user with higher privileges, this could lead to performing actions with that user's credentials. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin, and only affects sites using TableBlock.

Patches

Patched versions have been released as Wagtail 6.3.8, 7.0.6, 7.2.3 and 7.3.1.

Workarounds

Site owners who are unable to upgrade to the new versions can remediate the vulnerability by setting a template attribute on all TableBlock definitions, referencing a template that does not output class attributes. For example:

<!-- For use with TableBlock(template="path/to/table_block.html") -->
<table>
    {% if table_caption %}
        <caption>{{ table_caption }}</caption>
    {% endif %}
    {% if table_header %}
        <thead>
            <tr>
                {% for cell in table_header %}
                    <th scope="col">{{ cell }}</th>
                {% endfor %}
            </tr>
        </thead>
    {% endif %}
    <tbody>
        {% for row in data %}
            <tr>
                {% for cell in row %}
                    {% if first_col_is_header and forloop.first %}
                        <th scope="row">{{ cell }}</th>
                    {% else %}
                        <td>{{ cell }}</td>
                    {% endif %}
                {% endfor %}
            </tr>
        {% endfor %}
    </tbody>
</table>

Acknowledgements

Many thanks to Guan Chenxian (@GCXWLP) for reporting this issue.

For more information

If there are any questions or comments about this advisory:

• Visit Wagtail's support channels
• Email Wagtail at security@wagtail.org (view the security policy for more information).