Rule:

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Sid:
1925

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Summary:
This event is generated when a request is made to Network File System (NFS) to list all exported file systems and to indicate which clients are permitted to mount each file system. 

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Impact:
Information disclosure.  This can allow an attacker to discover exported NFS file systems and client mount permissions.

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Detailed Information:
The mountd Remote Procedure Call (RPC) implements the NFS mount protocol.  When an NFS client requests a mount of an NFS file system, mountd examines the list of exported file systems.  If the NFS client is permitted access to the requested file system, mountd returns a file handle for the requested directory.  An attacker or legitimate NFS client may request a list of exported file systems and client mount permissions.

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Affected Systems:
All systems running NFS.

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Attack Scenarios:
An attacker may attempt to list the exported NFS file systems as a precursor to mounting them to read or change a specific file. 

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Ease of Attack:
Simple.   

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False Positives:
If a legitimate remote user is allowed to list exported NFS file systems, this rule may trigger.

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False Negatives:
None Known.

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Corrective Action:
Limit remote access to RPC services.

Filter RPC ports at the firewall to ensure access is denied to RPC-enabled machines. 

Disable unneeded RPC services.

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Contributors:
Original rule written by Brian Caswell <bmc@sourcefire.com>
Sourcefire Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:
http://www.whitehats.com/info/IDS26


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