By passing specific HTTP headers to the document serve URL endpoint, an attacker was able to determine whether a document with a given ID matched a specified SHA1 hash, regardless of any permission restrictions on the document or knowing its filename. This could allow an attacker to determine whether a document with a specific known hash is present in the Wagtail document library.

This vulnerability does not expose the document's contents or any metadata beyond the already known SHA1 hash, and does not expose information about any documents for which the attacker does not know the SHA1 hash.

Patched versions have been released as Wagtail 7.0.9, 7.3.4, 7.4.3 and 8.0rc2.

Site owners who are unable to upgrade can strip If-Match and If-None-Match from anonymous requests to /documents/ at the reverse proxy, or use a custom document model without a file hash attribute.

Many thanks to Anand Himanshu for reporting this issue.

If you have any questions or comments about this advisory: