Rule:  

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Sid:
530

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Summary:
This event is generated when an attacker sends a blank username and blank password in an attempt to connect to the IPC$ (Interprocess Communication) pipe.

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Impact:
Information gathering. This attack can permit the disclosure of sensitive information about the target host.

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Detailed Information:
Null sessions allow browsing of Windows hosts by the "Network Neighborhood" and other functions.  A Null session permits access to a host using a blank user name and password.  At attacker may attempt to perform a Null session connection, disclosing sensitive information about the target host such as available shares and user names.

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Affected Systems:
Microsoft Windows hosts

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Attack Scenarios:
An attacker can send a blank username and blank password to try to connect to the IPC$ hidden share on the target computer.

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Ease of Attack:
Simple.

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False Positives:
Null sessions may be used by legitimate processes in the same Windows domain.  

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False Negatives:
None Known

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Corrective Action:
On Windows NT, 2000, XP set the registry key /System/CurrentControlSet/Control/LSA/RestrictAnonymous value to 1.

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Contributors:
Original rule written by Ian Viket <ian.vitek@infosec.se>
Documented by Nawapong Nakjang <tony@ksc.net, tonie@thai.com>
Sourcefire Research Team
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

CVE
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-1999-0519

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