Collabora Online is a collaborative online office suite based on LibreOffice technology. Users of Nextcloud with Collabora Online Built-in CODE Server app can be vulnerable to attack via proxy.php. This vulnerability has been fixed in Collabora Online - Built-in CODE Server (richdocumentscode) release 23.5.403. Users are advised to upgrade. There are no known workarounds for this vulnerability.
https://github.com/CollaboraOnline/online/security/advisories/GHSA-qjrm-q4h5-v3r2