Discourse is an open source platform for community discussion. In affected versions an attacker can trick a target user to make changes to their own username via carefully crafted link using the `activate-account` route. This problem has been patched in the latest version of Discourse. Users are advised to upgrade. There are no known workarounds for this vulnerability.
https://github.com/discourse/discourse/security/advisories/GHSA-gvpp-v7mp-wxxw