Fixed in ClickHouse Release 19.14.3.3, 2019-09-10

Аn attacker that has write access to ZooKeeper and who can run a custom server available from the network where ClickHouse runs, can create a custom-built malicious server that will act as a ClickHouse replica and register it in ZooKeeper. When another replica will fetch data part from the malicious replica, it can force clickhouse-server to write to arbitrary path on filesystem.