🛠️NFS

Theory

NFS or Network File system allows a client to access files over a network in the same way they would access a local storage file.

A NFS server determines what ressources to make available and ensures to recognize validated clients. From the client perspective, the machine requests access to a share by issuing a mount request. If successful the client can view and interact with the share as if its his own disk.

This service is located on the port 2049.

Practice

Enumerate mountable directories.

To check which share is available for mount, showmount can be used.

showmount -e <TARGET_IP> 
/ *    -> means that the root directory is shared to everyone on the network
/ <IP> -> means that the root directory is shared with <IP>

Mounting directories.

A local directory where the shared directory will be mounted is necessary.

mkdir /tmp/local_directory
mount -t nfs <IP>:/directory /tmp/infosec

Exploiting NFS weak permissions

no_root_squash

Root squashing is a configuration that prevents remote root users to get a root access on the mounted NFS volume. Enabled by default remote root users are assigned as nfsnobody , which is a role that has the least local privileges.

Alternatively "no_root_squash" parameter turns off this configuration and gives to the remote user, root access to the NFS volume.

NFS no_root_squash/no_all_squash misconfiguration PEHackTricks

Resources