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Title: Flaw In Winsock Proxy Service And ISA Firewall Service Can Cause Denial Of Service (331066) Date: 09 April 2003 Software: Microsoft Proxy Server 2.0, Microsoft ISA Server Impact: denial of service Max Risk: Important Bulletin: MS03-012
Microsoft encourages customers to review the Security Bulletins at:
There is a flaw in the Winsock Proxy service in Microsoft Proxy Server 2.0, and the Microsoft Firewall service in ISA Server 2000, that would allow an attacker on the internal network to send a specially crafted packet that would cause the server to stop responding to internal and external requests. Receipt of such a packet would cause CPU utilization on the server to reach 100%, and thus make the server unresponsive. The Winsock Proxy service and Microsoft Firewall service work with FTP, telnet, mail, news, Internet Relay Chat (IRC), or other client applications that are compatible with Windows Sockets (Winsock). These services allow these applications to perform as if they were directly connected to the Internet. These services redirect the necessary communications functions to a Proxy Server 2.0 or ISA Server computer, thus establishing a communication path from the internal application to the Internet through it.
A patch is available to fix this vulnerability. Please read the Security Bulletins at
for information on obtaining this patch.
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