GEN:SID 1:275
Message DOS NAPTHA
Summary This event is generated when a remote attacker transmits a malformed TCP packet to an internal server. This may indicate a "NAPTHA" Denial of Service (DoS) attack.
Impact Denial of service.
Detailed Information An attacker can craft a TCP packet that, when transmitted to the target server, maintains the TCP session on the target server in an unresolved state. This consumes system resources and overwhelms the target server, causing the server to stop responding to other network requests. In some cases, this type of attack can crash the target server.  
Affected Systems Microsoft Windows 95
Microsoft Windows 98
Microsoft Windows 98SE
Microsoft Windows Millennium
Windows NT 4.0
HP-UX 11
IBM AIX 4.3
Sun Solaris 7-8
FreeBSD 4.0-REL
Redhat Linux 6.1 - 7.0
Other Linux operating systems based on the Linux 2.0 kernel

Attack Scenarios An attacker sends a number of malformed TCP packets to a target computer. The computer attempts to maintain all incoming connections, causing it to slow down or stop responding to legitimate network requests.
Ease of Attack Simple. Exploits exist.
Corrective Action Install the latest patches available for your operating system. Patches and workarounds for Microsoft are available at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS00-091.asp.
Additional References  
Rule References url: www.cert.org/advisories/CA-2000-21.html
url: razor.bindview.com/publish/advisories/adv_NAPTHA.html
bugtraq: 2022
cve: 2000-1039
url: www.microsoft.com/technet/security/bulletin/MS00-091.mspx