demo.nextcloud.com: Content spoofing due to default Apache Error Page

How it was found

Hello there , your site is vulnerable to phishing the users by this vulnerability.

proof of concept https://demo.nextcloud.com///Hello---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------our%20website%20is%20down%20now%20you%20can%20visit%20this%20domain%20mydomain.com%20as%20this%20domain%20doesn't%20exist%20.

Thanks !