How to Use the Command 'nxc nfs' (with Examples)

The ’nxc nfs’ command is a versatile tool designed for pentesting and exploiting NFS (Network File System) servers. It is especially useful for security professionals who need to identify vulnerabilities in NFS implementations, as it currently supports only accessing NFS servers in anonymous mode. This command helps in identifying potential attack vectors by allowing users to gather information about the NFS servers, such as the version in use, available shares, and file contents. It also provides functionalities to both download and upload files to shares, facilitating a comprehensive assessment of the server’s security.

Use case 1: Detect the version of a remote NFS server

Code:

nxc nfs 192.168.178.0/24

Motivation:

Detecting the NFS server version is crucial for identifying vulnerabilities specific to that version. Older versions may have well-documented vulnerabilities that can be exploited, so understanding what version is running can help in prioritizing actions and mitigating risks. Additionally, knowing the version can assist in determining the NFS server’s compatibility with certain features or commands.

Explanation:

• nxc: This specifies the command’s toolset.
• nfs: This dictates that the NFS module of the tool is being used.
• 192.168.178.0/24: This represents the IP address range of the network where potentially multiple NFS servers might exist. The /24 indicates a subnet mask that covers all IP addresses from 192.168.178.0 to 192.168.178.255, allowing the command to detect NFS servers within this network range.

Example Output:

Scanning for NFS servers...
Detected NFS server at 192.168.178.1
Server Version: 3.0
Detected NFS server at 192.168.178.2
Server Version: 4.1

Use case 2: List the available NFS shares

Code:

nxc nfs 192.168.178.2 --shares

Motivation:

Listing available NFS shares on a server gives insight into what resources are being shared over the network. This can help in understanding the data exposure and accessibility risks associated with these shares, particularly in identifying directories or files that might have sensitive information or insecure configurations.

Explanation:

• 192.168.178.2: The specific IP address of the NFS server from which you want to list available shares.
• --shares: A flag that instructs the command to list the NFS shares available on the specified server.

Example Output:

Fetching available shares from 192.168.178.2...
Share 1: /public
Share 2: /backup
Share 3: /media

Use case 3: Enumerate the exposed shares recursively to the specified depth

Code:

nxc nfs 192.168.178.2 --enum-shares 5

Motivation:

By recursively enumerating the contents of shares up to a certain depth, users can explore the directory structure and the files contained within. This process aids in identifying potential security issues such as exposed sensitive files or directories. It also gives a clearer understanding of how data is structured and made accessible within the share.

Explanation:

• 192.168.178.2: The target IP address of the NFS server.
• --enum-shares: A command option that triggers the enumeration process for the NFS shares.
• 5: The depth of recursion, indicating that the command should explore the directory structure up to 5 levels deep. This depth can be adjusted based on how deeply nested the file structures are expected to be.

Example Output:

Enumerating shares on 192.168.178.2...
Share: /public
  Level 1: folder1
  Level 2: folder2/subfolder
    File: file.txt
  Level 5: folder5/file5.doc
Share: /backup
  Level 1: week1/backup.tar.gz

Use case 4: Download the specified remote file

Code:

nxc nfs 192.168.178.2 --get-file path/to/remote_file path/to/local_file

Motivation:

Downloading a remote file is a critical function in pentesting, as it allows analysts to review files for sensitive information that might have been improperly secured. By accessing and examining these files, security professionals can assess data exposure risks and advise on the necessary protective measures.

Explanation:

• 192.168.178.2: The IP of the NFS server from which the file will be downloaded.
• --get-file: The option specifying the action of downloading a file from a share.
• path/to/remote_file: Represents the full path to the file on the remote NFS server that needs to be downloaded.
• path/to/local_file: The local path where the downloaded file should be stored.

Example Output:

Connecting to 192.168.178.2...
Downloading file '/remote/path/to/remote_file' to '/local/path/to/local_file'...
Download complete.

Use case 5: Upload the specified local file to the remote share

Code:

nxc nfs 192.168.178.2 --put-file path/to/local_file path/to/remote_file

Motivation:

Uploading files to an NFS server can test the server’s controls regarding write permissions. It indicates whether unauthorized users can upload potentially harmful files, thus assisting in assessing the misconfigurations or vulnerabilities within the server’s security posture and permissions configuration.

Explanation:

• 192.168.178.2: The IP address of the target NFS server where the file will be uploaded.
• --put-file: The command option used to upload a local file to the NFS server.
• path/to/local_file: The path of the file on your local machine that you want to upload.
• path/to/remote_file: The intended path on the remote NFS server where the file should be placed.

Example Output:

Connecting to 192.168.178.2...
Uploading file '/local/path/to/local_file' to '/remote/path/to/remote_file'...
Upload successful.

Conclusion:

The ’nxc nfs’ command provides essential functionality for pentesters and security professionals working with NFS servers. From discerning server versions to accessing and managing file shares, this toolset helps in the thorough assessment and identification of vulnerabilities. By mastering these use cases, users can ensure enhanced security assessments and better protection of their network systems. For further details and advanced usage, consult the documentation at https://www.netexec.wiki/nfs-protocol .