GHSA-wq5h-f9p5-q7fx Improper validation of URLs ('Cross-site Scripting') in Wagtail rich text fields

• PyPI wagtail: < 2.11.7 → fixed in 2.11.7 • PyPI wagtail: >= 2.12, < 2.12.4 → fixed in 2.12.4

Impact When saving the contents of a rich text field in the admin interface, Wagtail does not apply server-side checks to ensure that link URLs use a valid protocol. A malicious user with access to the admin interface could thus craft a POST request to publish content with `javascript:` URLs containing arbitrary code. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin. Patches Patched versions have been released as Wagtail 2.11.7 (for the LTS 2.11 branch) and Wagtail 2.12.4 (for the current 2.12 branch). Workarounds For sites that cannot easily upgrade to a current supported version, the vulnerability can be patched by adding the following code to a `wagtail_hooks.py` module in any installed app: ```python from draftjs_exporter.dom import DOM from wagtail.admin.rich_text.converters.html_to_contentstate import ExternalLinkElementHandler, PageLinkElementHandler from wagtail.core import hooks from wagtail.core.whitelist import check_url def link_entity(props): id_ = props.get('id') link_props = {} if id_ is not None: link_props['linktype'] = 'page' link_props['id'] = id_ else: link_props['href'] = check_url(props.get('url')) return DOM.create_element('a', link_props, props['children']) @hooks.register('register_rich_text_features', order=1) def register_link(features): features.register_converter_rule('contentstate', 'link', { 'from_database_format': { 'a[href]': ExternalLinkElementHandler('LINK'), 'a[linktype="page"]': PageLinkElementHandler('LINK'), }, 'to_database_format': { 'entity_decorators': {'LINK': link_entity} } }) ``` Acknowledgements Many thanks to Kevin Breen for reporting this issue. For more information If you have any questions or comments about this advisory: • Visit Wagtail's support channels • Email us at [email protected] (if you wish to send encrypted email, the public key ID is `0x6ba1e1a86e0f8ce8`)