Nextcloud Android app is the Android client for Nextcloud, a self-hosted productivity platform. In versions prior to 3.19.0, any application with notification permission can access contacts if Nextcloud has access to Contacts without applying for the Contacts permission itself. Version 3.19.0 contains a fix for this issue. There are currently no known workarounds.
https://hackerone.com/reports/1161401
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-5cj3-v98r-2wmq