Discourse is the an open source discussion platform. In affected versions a maliciously crafted request for static assets could cause error responses to be cached by Discourse's default NGINX proxy configuration. A corrected NGINX configuration is included in the latest stable, beta and tests-passed versions of Discourse. Users are advised to upgrade. There are no known workarounds for this vulnerability.
https://github.com/discourse/discourse/security/advisories/GHSA-4ff8-3j78-w6pp
https://github.com/discourse/discourse/commit/7af25544c3940c4d046c51f4cfac9c72a06d4f50