In Bitcoin Knots v0.11.0.ljr20150711 through v0.13.0.knots20160814 (fixed in v0.13.1.knots20161027), the debug console stores sensitive information including private keys and the wallet passphrase in its persistent command history.
Bitcoin Core 0.12.0 through 0.17.1 and Bitcoin Knots 0.12.0 through 0.17.x before 0.17.1.knots20181229 have Incorrect Access Control. Local users can exploit this to steal currency by binding the RPC IPv4 localhost port, and forwarding requests to the IPv6 localhost port.