Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. Prior to 5.5.3, a stored HTML injection in the Mail app's message list allowed an authenticated user to inject HTML into the email subjects. Javascript was correctly blocked by the content security policy of the Nextcloud Server code.
Nextcloud Mail is the mail app for Nextcloud, a self-hosted productivity platform. When a user is trying to set up a mail account with an email address like user@example.tld that does not support auto configuration, and an attacker managed to register autoconfig.tld, the used email details would be send to the server of the attacker. It is recommended that the Nextcloud Mail app is upgraded to 1.14.6, 1.15.4, 2.2.11, 3.6.3, 3.7.7 or 4.0.0.