Read the _ **/etc/exports** _ file, if you find some directory that is configured as **no\_root\_squash**, then you can **access** it from **as a client** and **write inside** that directory **as** if you were the local **root** of the machine.
**no\_root\_squash**: This option basically gives authority to the root user on the client to access files on the NFS server as root. And this can lead to serious security implications.
**no\_all\_squash:** This is similar to **no\_root\_squash** option but applies to **non-root users**. Imagine, you have a shell as nobody user; checked /etc/exports file; no\_all\_squash option is present; check /etc/passwd file; emulate a non-root user; create a suid file as that user (by mounting using nfs). Execute the suid as nobody user and become different user.
* **Mounting that directory** in a client machine, and **as root copying** inside the mounted folder the **/bin/bash** binary and giving it **SUID** rights, and **executing from the victim** machine that bash binary.
* **Mounting that directory** in a client machine, and **as root copying** inside the mounted folder our come compiled payload that will abuse the SUID permission, give to it **SUID** rights, and **execute from the victim** machine that binary (you can find here some[ C SUID payloads](payloads-to-execute.md#c)).
Note that if you can create a **tunnel from your machine to the victim machine you can still use the Remote version to exploit this privilege escalation tunnelling the required ports**.\
The following trick is in case the file `/etc/exports`**indicates an IP**. In this case you **won't be able to use** in any case the **remote exploit** and you will need to **abuse this trick**.\
Another required requirement for the exploit to work is that **the export inside `/etc/export`****must be using the `insecure` flag**.\
Now, let’s assume that the share server still runs `no_root_squash` but there is something preventing us from mounting the share on our pentest machine. This would happen if the `/etc/exports` has an explicit list of IP addresses allowed to mount the share.
Listing the shares now shows that only the machine we’re trying to privesc on is allowed to mount it:
This means that we’re stuck exploiting the mounted share on the machine locally from an unprivileged user. But it just so happens that there is another, lesser known local exploit.
This exploit relies on a problem in the NFSv3 specification that mandates that it’s up to the client to advertise its uid/gid when accessing the share. Thus it’s possible to fake the uid/gid by forging the NFS RPC calls if the share is already mounted!
Here’s a [library that lets you do just that](https://github.com/sahlberg/libnfs).
Once local root on the machine, I wanted to loot the NFS share for possible secrets that would let me pivot. But there were many users of the share all with their own uids that I couldn’t read despite being root because of the uid mismatch. I didn’t want to leave obvious traces such as a chown -R, so I rolled a little snippet to set my uid prior to running the desired shell command:
```python
#!/usr/bin/env python
import sys
import os
def get_file_uid(filepath):
try:
uid = os.stat(filepath).st_uid
except OSError as e:
return get_file_uid(os.path.dirname(filepath))
return uid
filepath = sys.argv[-1]
uid = get_file_uid(filepath)
os.setreuid(uid, uid)
os.system(' '.join(sys.argv[1:]))
```
You can then run most commands as you normally would by prefixing them with the script:
