18.7. Preventing Server Spoofing
While the server is running, it is not possible for a malicious user
to take the place of the normal database server. However, when the
server is down, it is possible for a local user to spoof the normal
server by starting their own server. The spoof server could read
passwords and queries sent by clients, but could not return any data
PGDATA directory would still be secure because
of directory permissions. Spoofing is possible because any user can
start a database server; a client cannot identify an invalid server
unless it is specially configured.
One way to prevent spoofing of
connections is to use a Unix domain socket directory (unix_socket_directories) that has write permission only
for a trusted local user. This prevents a malicious user from creating
their own socket file in that directory. If you are concerned that
some applications might still reference
/tmp for the
socket file and hence be vulnerable to spoofing, during operating system
startup create a symbolic link
/tmp/.s.PGSQL.5432 that points
to the relocated socket file. You also might need to modify your
/tmp cleanup script to prevent removal of the symbolic link.
Another option for
local connections is for clients to use
to specify the required owner of the server process connected to
To prevent spoofing on TCP connections, the best solution is to use
SSL certificates and make sure that clients check the server's certificate.
To do that, the server
must be configured to accept only
hostssl connections (Section 20.1) and have SSL key and certificate files
(Section 18.9). The TCP client must connect using
verify-full and have the appropriate root certificate
file installed (Section 33.18.1).