ServerBuddies Support Blog

Securing Portmap service

The portmap service is a dynamic port assignment daemon for RPC services such as NIS and NFS. It has weak authentication mechanisms and has the ability to assign a wide range of ports for the services it controls. For these reasons, it is difficult to secure.

NFSv4 no longer requires it. If you plan to implement a NFSv2 or NFSv3 server, then portmap is required.

It is important to use TCP wrappers to limit which networks or hosts have access to the portmap service since it has no built-in form of authentication.

Further, use only IP addresses when limiting access to the service. Avoid using hostnames, asthey can be forged via DNS poisoning and other methods.

Below are two example IPTables commands that allow TCP connections to the portmap service (listening on port 111) from the 192.168.0/24 network and from the localhost. All other packets are dropped.

To similarly limit UDP traffic, use the following command.

Protect portmap With iptables

The portmap service is a dynamic port assignment daemon for RPC services such as NIS and NFS. It has weak authentication mechanisms and has the ability to assign a wide range of ports for the services it controls. For these reasons, it is difficult to secure.

Securing portmap only affects NFSv2 and NFSv3 implementations, since NFSv4 no longer requires it. If you plan to implement an NFSv2 or NFSv3 server, then portmap is required, and the following section applies.

Below are two example iptables commands. The first allows TCP connections to the port 111 (used by the portmap service) from the 192.168.0.0/24 network. The second allows TCP connections to the same port from the localhost.

Example:

To similarly limit UDP traffic, use the following command.