Impact

When the {% include_block %} template tag is used to output the value of a plain-text StreamField block (CharBlock, TextBlock or a similar user-defined block derived from FieldBlock), and that block does not specify a template for rendering, the tag output is not properly escaped as HTML. This could allow users to insert arbitrary HTML or scripting. This vulnerability is only exploitable by users with the ability to author StreamField content (i.e. users with 'editor' access to the Wagtail admin).

Patches

Patched versions have been released as Wagtail 2.11.8 (for the LTS 2.11 branch), Wagtail 2.12.5, and Wagtail 2.13.2 (for the current 2.13 branch).

Site implementors who wish to retain the existing behaviour of allowing editors to insert HTML content in these blocks (and are willing to accept the risk of untrusted editors inserting arbitrary code) may disable the escaping by surrounding the relevant {% include_block %} tag in {% autoescape off %}...{% endautoescape %}.

Workarounds

Site implementors who are unable to upgrade to a current supported version should audit their use of {% include_block %} to ensure it is not used to output CharBlock / TextBlock values with no associated template. Note that this only applies where {% include_block %} is used directly on that block (uses of include_block on a block containing a CharBlock / TextBlock, such as a StructBlock, are unaffected). In these cases, the tag can be replaced with Django's {{ ... }} syntax - e.g. {% include_block my_title_block %} becomes {{ my_title_block }}.

Acknowledgements

Many thanks to Karen Tracey 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 security@wagtail.io (if you wish to send encrypted email, the public key ID is 0x6ba1e1a86e0f8ce8)