Microsoft Security Bulletin MS03-026: Buffer Overrun In RPC Interface Could Allow Code Execution(Q823980)

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Title:      Buffer Overrun In RPC Interface Could Allow Code 
            Execution (823980)

Date:       16 July 2003
Software:   Microsoft(r) Windows (r) NT 4.0
            Microsoft Windows NT 4.0 Terminal Services Edition 
            Microsoft Windows 2000 
            Microsoft Windows XP 
            Microsoft Windows Server 2003 
Impact:     Run code of attacker's choice
Max Risk:   Critical
Bulletin:   MS03-026

Microsoft encourages customers to review the Security Bulletins 
at: 
http://www.microsoft.com/technet/security/bulletin/MS03-026.asp
http://www.microsoft.com/security/security_bulletins/MS03-026.asp
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Issue:
======

Remote Procedure Call (RPC) is a protocol used by the Windows 
operating system. RPC provides an inter-process communication 
mechanism that allows a program running on one computer to 
seamlessly execute code on a remote system. The protocol itself 
is derived from the OSF (Open Software Foundation) RPC protocol, 
but with the addition of some Microsoft specific extensions. 

There is a vulnerability in the part of RPC that deals with 
message exchange over TCP/IP. The failure results because of 
incorrect handling of malformed messages. This particular 
vulnerability affects a Distributed Component Object Model (DCOM) 
interface with RPC, which listens on TCP/IP port 135. This 
interface handles DCOM object activation requests sent by client 
machines (such as Universal Naming Convention (UNC) paths) to the 
server. 

To exploit this vulnerability, an attacker would need to send a 
specially formed request to the remote computer on port 135. 


Mitigating factors: 
====================

 - To exploit this vulnerability, the attacker would require the 
ability to send a specially crafted request to port 135 on the 
remote machine. For intranet environments, this port would 
normally be accessible, but for Internet connected machines, the 
port 135 would normally be blocked by a firewall. In the case 
where this port is not blocked, or in an intranet configuration, 
the attacker would not require any additional privileges. 

 - Best practices recommend blocking all TCP/IP ports that are 
not actually being used. For this reason, most machines attached 
to the Internet should have port 135 blocked. RPC over TCP is not 
intended to be used in hostile environments such as the internet. 
More robust protocols such as RPC over HTTP are provided for 
hostile environments.

Risk Rating:
============
Critical

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read 
the  Security Bulletins at
   
http://www.microsoft.com/technet/security/bulletin/ms03-026.asp
http://www.microsoft.com/security/security_bulletins/ms03-026.asp
   
   for information on obtaining this patch.


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