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                              stake, Inc.
                            www.atstake.com
                           Security Advisory

Advisory Name: Norton Personal Internet Firewall HTTP Proxy
Vulnerability
 Release Date: 07/15/2002
  Application: AtGuard v3.2
               Norton Personal Internet Firewall 2001 v3.0.4.91
     Platform: Microsoft Windows NT4 SP6a
               Microsoft Windows 2000 SP2
     Severity: A buffer overflow occurs potentially allowing the
               execution of arbitrary code
       Author: Ollie Whitehouse (ollieatstake.com)
Vendor Status: Informed and patch available
CVE Candidate: CAN-2002-0663
    Reference: www.atstake.com/research/advisories/2002/a071502-1.txt

Overview:

        Symantec (http://www.symantec.com/) Norton Personal Internet
Firewall is a widely used desktop firewalling application for
Microsoft Windows NT, 98, ME and 2000 platforms. Typically personal
firewalls are deployed upon mobile workstations that leave the
enterprise
and may be deployed upon public networks to enable them to establish
connectivity back to the corporation and thus require protection from
malicious attackers while outside the confines of the enterprise
firewall.

There exists a vulnerability within the NPIF's HTTP proxy that allows an
attacker to overwrite the first three (3) bytes of the EDI register and
Thus potentially execute malicious code.

This vulnerability is exploitable even if the requesting application is
not configured in the firewall permission setting to make outgoing
requests. An example of such a scenario would be a malicious web page
that
contains a disguised link which contains sufficient data to exploit this
vulnerability.

Details:

        There is a vulnerability with the way in which the NT kernel
based
HTTP proxy of NPIF deals with a large amount of data, that causes a
buffer
overflow to occur. The test scenario that stake used to cause this
Exception was as follows:

NPIF configured to allow only Microsoft Internet Explorer out on TCP
port
80 to the public internet. A large outgoing request is then made by a
third
party application (i.e. malicious code). If the exploitation is
unsuccessful a NT kernel exception will be thrown typically overwriting
EDI
with user supplied data. If exploitation is successful an attacker can
run
arbitrary code within the KERNEL.

Vendor Response:

This issue was reported to Symantec on April 18, 2002. Symantec has an
Update that solves this problem. Symantec's advisory regarding this
issue
can be found here (wrapped):
http://securityresponse.symantec.com/avcenter/security/
SymantecAdvisories.html

Recommendations:

Due to the fact that this attack has to occur from the host computer
stake recommends that there should be a multi-layered approach to
security. This should include anti-virus, user education/awareness as
well as ensuring that vendor patches are deployed for all relevant
software products.

Users should install the update for Norton Personal Internet Firewall
2001.

Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has
assigned the following names to these issues. These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

 CAN-2002-0663 Norton Personal Internet Firewall Buffer Overflow

stake Vulnerability Reporting Policy:
http://www.atstake.com/research/policy/

stake Advisory Archive:
http://www.atstake.com/research/advisories/

PGP Key:
http://www.atstake.com/research/pgp_key.asc

Copyright 2002 stake, Inc. All rights reserved.

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