hacktricks/network-services-pentesting/nfs-service-pentesting.md

# 2049 - Pentesting NFS Service

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## **Basic Information**

It is a client/server system that allows users to access files across a network and treat them as if they resided in a local file directory. It has the same purpose as SMB but it cannot talk to SMB.

The NFS protocol has **no mechanism for authentication** or **authorization**. The authorization is taken from the available information of the file system where the server is responsible for translating the **user information** supplied by the **client** to that of the **file system** and converting the corresponding authorization information as correctly as possible into the syntax required by UNIX.

The most common **authentication is via UNIX `UID`/`GID` and `group memberships`**, which is why this syntax is most likely to be applied to the NFS protocol. One problem is that the **client** and **server** do **not necessarily** have to have the **same mappings of UID/GID** to users and groups. No further checks can be made on the part of the server. This is why NFS should **only** be used with this authentication method in **trusted networks**.

**Default port**: 2049/TCP/UDP (except version 4, it just needs TCP or UDP).&#x20;

```
2049/tcp open  nfs     2-3 (RPC #100003
```

### Versions

(From [https://academy.hackthebox.com/module/112/section/1068](https://academy.hackthebox.com/module/112/section/1068))

| **Version** | **Features**                                                                                                                                                                                                                                                                 |
| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `NFSv2`     | It is **older** but is supported by many systems and was initially operated entirely over UDP.                                                                                                                                                                               |
| `NFSv3`     | It has more features, including variable file size and better error reporting, but is not fully compatible with NFSv2 clients.                                                                                                                                               |
| `NFSv4`     | It includes Kerberos, works through firewalls and on the Internet, **no longer requires portmappers**, supports ACLs, applies state-based operations, and provides performance improvements and high **security**. It is also the first version to have a stateful protocol. |

## Enumeration

### Useful nmap scripts

```bash
nfs-ls #List NFS exports and check permissions
nfs-showmount #Like showmount -e
nfs-statfs #Disk statistics and info from NFS share
```

### Useful metasploit modules

```bash
scanner/nfs/nfsmount #Scan NFS mounts and list permissions
```

### Mounting

To know **which folder** has the server **available** to mount you an ask it using:

```bash
showmount -e <IP>
```

Then mount it using:

```bash
mount -t nfs [-o vers=2] <ip>:<remote_folder> <local_folder> -o nolock
```

You should specify to **use version 2** because it doesn't have **any** **authentication** or **authorization**.

**Example:**

```bash
mkdir /mnt/new_back
mount -t nfs [-o vers=2] 10.12.0.150:/backup /mnt/new_back -o nolock
```

## Permissions

If you mount a folder which contains **files or folders only accesible by some user** (by **UID**). You can **create** **locally** a user with that **UID** and using that **user** you will be able to **access** the file/folder.

## NSFShell

To easily list, mount and change UID and GID to have access to files you can use [nfsshell](https://github.com/NetDirect/nfsshell).

[Nice NFSShell tutorial.](https://www.pentestpartners.com/security-blog/using-nfsshell-to-compromise-older-environments/)

## Config files

```
/etc/exports
/etc/lib/nfs/etab
```

### Dangerous settings

(From [https://academy.hackthebox.com/module/112/section/1068](https://academy.hackthebox.com/module/112/section/1068))

| **Option**       | **Description**                                                                                                      |
| ---------------- | -------------------------------------------------------------------------------------------------------------------- |
| `rw`             | Read and write permissions.                                                                                          |
| `insecure`       | Ports above 1024 will be used.                                                                                       |
| `nohide`         | If another file system was mounted below an exported directory, this directory is exported by its own exports entry. |
| `no_root_squash` | All files created by root are kept with the UID/GID 0.                                                               |
| `no_all_squash`  |                                                                                                                      |

## Privilege Escalation using NFS misconfigurations

[NFS no\_root\_squash and no\_all\_squash privilege escalation](../linux-hardening/privilege-escalation/nfs-no\_root\_squash-misconfiguration-pe.md)

## HackTricks Automatic Commands

```
Protocol_Name: NFS    #Protocol Abbreviation if there is one.
Port_Number:  2049     #Comma separated if there is more than one.
Protocol_Description: Network File System         #Protocol Abbreviation Spelled out

Entry_1:
  Name: Notes
  Description: Notes for NFS
  Note: |
    It is a client/server system that allows users to access files across a network and treat them as if they resided in a local file directory.

    #apt install nfs-common
    showmount 10.10.10.180      ~or~showmount -e 10.10.10.180
    should show you available shares (example /home)

    mount -t nfs -o ver=2 10.10.10.180:/home /mnt/
    cd /mnt
    nano into /etc/passwd and change the uid (probably 1000 or 1001) to match the owner of the files if you are not able to get in

    https://book.hacktricks.xyz/pentesting/nfs-service-pentesting

Entry_2:
  Name: Nmap
  Description: Nmap with NFS Scripts
  Command: nmap --script=nfs-ls.nse,nfs-showmount.nse,nfs-statfs.nse -p 2049 {IP}
```

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