/usr/share/php/sabre21/Sabre/CardDAV/ is in php-sabre-dav-2.1 2.1.10-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/sabre21/Sabre/CardDAV/AddressBook.php
/usr/share/php/sabre21/Sabre/CardDAV/AddressBookQueryParser.php
/usr/share/php/sabre21/Sabre/CardDAV/AddressBookRoot.php
/usr/share/php/sabre21/Sabre/CardDAV/Backend/
/usr/share/php/sabre21/Sabre/CardDAV/Backend/AbstractBackend.php
/usr/share/php/sabre21/Sabre/CardDAV/Backend/BackendInterface.php
/usr/share/php/sabre21/Sabre/CardDAV/Backend/PDO.php
/usr/share/php/sabre21/Sabre/CardDAV/Backend/SyncSupport.php
/usr/share/php/sabre21/Sabre/CardDAV/Card.php
/usr/share/php/sabre21/Sabre/CardDAV/IAddressBook.php
/usr/share/php/sabre21/Sabre/CardDAV/ICard.php
/usr/share/php/sabre21/Sabre/CardDAV/IDirectory.php
/usr/share/php/sabre21/Sabre/CardDAV/Plugin.php
/usr/share/php/sabre21/Sabre/CardDAV/Property/
/usr/share/php/sabre21/Sabre/CardDAV/Property/SupportedAddressData.php
/usr/share/php/sabre21/Sabre/CardDAV/Property/SupportedCollationSet.php
/usr/share/php/sabre21/Sabre/CardDAV/UserAddressBooks.php
/usr/share/php/sabre21/Sabre/CardDAV/VCFExportPlugin.php