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From: advisories at (advisories)
Subject: Corsaire Security Advisory - Sygate Enforcer discovery packet DoS issue

-- Corsaire Security Advisory --

Title: Sygate Enforcer discovery packet DoS issue
Date: 20.11.03
Application: Sygate Enforcer 4.0 and prior
Environment: Windows NT, 2000, 2003
Author: Martin O'Neal []
Audience: General distribution
Reference: c031120-001

-- Scope --

The aim of this document is to clearly define an issue that exists with 
the Sygate Enforcer product [1] that will allow a remote attacker to 
provoke a DoS condition. 

-- History --

Discovered: 20.11.03 (Martin O'Neal)
Vendor notified: 14.01.04
Document released: 10.8.04

-- Overview --

Sygate Enforcers are described as [2] "network gateway devices that 
enforce host integrity at network access points". Architecturally they 
function as an authenticated, packet-filtering firewall device. The 
Enforcer interacts with the Sygate Security Agent (SAA [the personal 
firewall component]) product and limits access to protected 
networks/hosts to authenticated clients that comply with a predefined 

In practise, the Enforcer device uses a number of proprietary protocol 
exchanges to communicate with other Enforcers and also the SAA product. 
By sending a packet containing a malformed payload to the Enforcer, the 
host service can be forced to stop responding.

-- Analysis --

The Sygate Enforcer product sends a discovery packet at one-second 
intervals on all interfaces that have IP bound to them. The packet is a 
UDP datagram, from source port 39999 to destination port 39999, and is 
sent to the local subnet broadcast address.

If this packet is malformed and replayed to the Enforcer, it will cause 
the Enforcer service to stop unexpectedly, without generating an entry 
within the product's audit trail.

It is worth noting that the packet that is replayed does not need to be 
sent to the local subnet broadcast address, and can be happily sent to 
any valid unicast address associated with the Enforcer. This means that 
the attacker does not need to be local to the Enforcer to exploit this 

-- Recommendations --

The Enforcer product should be upgraded to a version that is not 
susceptible to this issue.

-- Background --

This issue was discovered using a custom protocol analysis tool 
developed by Corsaire's security assessment team. This tool is not 
available publicly, but is an example of the specialist approach used by 
Corsaire's consultants as part of a commercial security assessment. To 
find out more about the cutting edge services provided by Corsaire 
simply visit our web site at

-- CVE --

The Common Vulnerabilities and Exposures (CVE) project has assigned
the name CAN-2003-0931 to this issue. This is a candidate for
inclusion in the CVE list (, which standardises
names for security problems.

-- References --


-- Revision --

a. Initial release.
b. Minor revisions.

-- Distribution --

This security advisory may be freely distributed, provided that it 
remains unaltered and in its original form. 

-- Disclaimer --

The information contained within this advisory is supplied "as-is" with 
no warranties or guarantees of fitness of use or otherwise. Corsaire 
accepts no responsibility for any damage caused by the use or misuse of 
this information.

-- About Corsaire --

Corsaire are a leading information security consultancy, founded in 1997 
in Guildford, Surrey, UK. Corsaire bring innovation, integrity and 
analytical rigour to every job, which means fast and dramatic security 
performance improvements. Our services centre on the delivery of 
information security planning, assessment, implementation, management 
and vulnerability research. 

A free guide to selecting a security assessment supplier is available at 

Copyright 2004 Corsaire Limited. All rights reserved. 

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