If a user was able to reuse an earlier used username, they could get access to any chat message sent to the previous user with this username.
It is recommended that the Nextcloud Talk App is upgraded to 11.2.2 or 11.3.0
Don't allow users to choose usernames themselves. This is the default behaviour of Nextcloud, but some user providers may allow doing so. (e.g. the registration app)
If you have any questions or comments about this advisory: