Users should choose a strong RPC password. If no RPC username and password are set, hush will not start and will print an error message with a suggestion for a strong random password. If the client knows the RPC password, they have at least full access to the node. In addition, certain RPC commands can be misused to overwrite files and/or take over the account that is running hushd. (In the future we may restrict these commands, but full node access – including the ability to spend from and export keys held by the wallet – would still be possible unless wallet methods are disabled.)
Users should also refrain from changing the default setting that only allows RPC connections from localhost. Allowing connections from remote hosts would enable a MITM to execute arbitrary RPC commands, which could lead to compromise of the account running hushd and loss of funds. For multi-user services that use one or more hushd instances on the backend, the parameters passed in by users should be controlled to prevent confused-deputy attacks which could spend from any keys held by that zcashd.
Hush has Delayed-Proof-of-Work, which drastically improves the Zcash rule-of-thumb of "re-organize 100 blocks to crash all ZEC full nodes in the world".
The option `-debug=zrpc` covers logging of the z_* calls. This will reveal information about private notes which you might prefer not to disclose. For example, when calling `z_sendmany` to create a shielded transaction, input notes are consumed and new output notes are created.
The option `-debug=zrpcunsafe` covers logging of sensitive information in z_* calls which you would only need for debugging and audit purposes. For example, if you want to examine the memo field of a note being spent.
Private spending keys for z addresses are never logged.
