On Unix systems (Linux, MacOS), Arc uses a temporary file with unsafe privileges. By tampering with such file, a malicious local user in the system may be able to trigger arbitrary code execution with root privileges.
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.