CVE-2021-43827: Discourse Footnote

Medium severity, CVSS 4.3. EPSS: 0.8% chance of exploitation in the next 30 days.

discourse-footnote is a library providing footnotes for posts in Discourse. ### Impact When posting an inline footnote wrapped in `<a>` tags (e.g. `<a>^[footnote]</a>`, the resulting rendered HTML would include a nested `<a>`, which is stripped by Nokogiri because it is not valid. This then caused a javascript error on topic pages because we were looking for an `<a>` element inside the footnote reference span and getting its ID, and because it did not exist we got a null reference error in javascript. Users are advised to update to version 0.2. As a workaround editing offending posts from the rails console or the database console for self-hosters, or disabling the plugin in the admin panel can mitigate this issue.

Affected products

• Discourse Discourse Footnote: before 0.2 (fixed in 0.2)

Published 2021-12-14. Last modified 2026-06-17.