[c-nsp] Cisco Security Advisory: Limitations in Cisco Secure Desktop

Mon Oct 9 12:00:58 EDT 2006

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Cisco Security Advisory: Limitations in Cisco Secure Desktop
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Advisory ID: cisco-sa-20061009-csd

http://www.cisco.com/warp/public/707/cisco-sa-20061009-csd.shtml

Revision 1.0

For Public Release 2006 October 09 1600 UTC (GMT)

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Summary
=======

Cisco has been made aware of limitations in the Cisco Secure Desktop (CSD)
product which may cause information accessed or produced during an SSL VPN
session to be left outside of the Secure Desktop environment.

There are no identified fixes, but there are some workarounds that can help
mitigate some of these limitations.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20061009-csd.shtml.

Affected Products
=================

The limitations described in this advisory exist in all versions of the Cisco
Secure Desktop product.

Details
=======

The Cisco Secure Desktop (CSD) seeks to minimize data from being left behind
after an SSL VPN session terminates. In particular, CSD works to reduce, via
encryption, the risk that cookies, browser history, temporary files, and
downloaded content remain on a system after a remote user logs out or an SSL
VPN session times out.

Cisco has been made aware of the following limitations in CSD that may cause
data accessed or produced during an SSL VPN session to be left outside of the
Secure Desktop environment:

Information Leakage via Windows Paging File
+------------------------------------------

This limitation is the inability to prevent data from leaking to the Windows
virtual memory file, which is commonly referred to as the paging file and is
called pagefile.sys. This file is normally located in the root directory of the
hard drive where Windows is installed, but it can also be a group of files
stored in various locations, across hard disks and partitions.

The paging file is used to store the contents of physical memory that have been
swapped out by the Windows kernel when there is pressure to provide additional
physical memory for some application, and no physical memory is available. In
this case, the Windows kernel swaps out memory used by idle processes to the
paging file and gives the de-allocated memory to the application that is asking
for more memory.

As a consequence of how the Windows virtual memory subsystem operates, the
physical memory contents used by any application, including those running in a
Secure Desktop, may end up in the paging file. The Windows paging file stores
"paged out" physical memory contents without encryption, and therefore
information "paged out" by the operating system may be recovered using data
forensic tools. Because of this process, CSD may not be able to remove from the
system all data produced and accessed during the SSL VPN session after the VPN
session terminates.

This item is not a CSD product defect. It is, rather, a CSD product limitation
resulting from how the Microsoft Windows operating system interacts with
applications.

Some possible workarounds may be an option when users have administrative
rights to their systems, as discussed in the Workarounds section.

Document Recovery via Windows Printer Spool Files
+------------------------------------------------

This limitation consists of an inability of CSD to prevent the recovery of
files used during an SSL VPN session. If the files have been printed, then they
can be recovered via the printer spool files, which are usually stored in the
directory C:\WINDOWS\system32\spool\PRINTERS\ and have .SPL extensions. These
files are short-lived because they are deleted after they have been
successfully sent to the printer. However, if there are printing problems, or
if data forensic methods are applied to the hard drive, they can be recovered.

For additional security, CSD provides an administrator-configurable option that
works to prevent printing from within a CSD session. This option is disabled by
default.

Inability to Detect Hardware Keystroke Loggers
+---------------------------------------------

This limitation consists of an inability to detect hardware keyloggers which
may be installed on the system on which CSD is running. This limitation stems
from the inability of an operating system to detect the presence of devices
that do not identify themselves, or that deliberately misrepresent their device
class.

Impact
======

The impact of the CSD limitations described in this advisory is that
information may be left behind on a computer after an SSL VPN session
terminates and after CSD has attempted to clean up all traces of the data
accessed or produced during the SSL VPN session.

Software Version and Fixes
==========================

There are no fixes for the limitations described in this advisory.

Workarounds
===========

Information Leakage via Windows Paging File
+------------------------------------------

The "Information Leakage via Windows Paging File" limitation can be mitigated
by configuring Windows to clear the paging file at shutdown. Instructions on
how to configure this are available at:

http://support.microsoft.com/kb/314834/EN-US/ (Windows XP)

http://support.microsoft.com/kb/182086/EN-US/ (Windows 2000)

Please note that this is an option only when administrative access to the
Windows system is available.

Document Recovery via Windows Printer Spool Files
+------------------------------------------------

For the "Document Recovery via Windows Printer Spool Files" limitation,
configuring CSD to prevent users from printing from within the Secure Desktop
will help mitigate the limitation. For information on how to do this please
refer to the Cisco Secure Desktop Configuration Guide, available at:

http://www.cisco.com/en/US/products/ps6742/products_configuration_guide_chapter09186a00805f9f42.html#wp1041681

Inability to Detect Hardware Keystroke Loggers
+---------------------------------------------

There are no workarounds for the inability to detect hardware keyloggers.

Exploitation and Public Announcements
=====================================

The Cisco PSIRT is not aware of any public announcements or malicious use of
the limitations described in this advisory.

The issues described in this advisory were discovered by a Cisco partner,
ManTech International Corporation, as part of a product security evaluation
commissioned by Cisco.

The "Information Leakage via Paging file" limitation was also independently
reported to Cisco by Rick Patterson, Information Security Group at Sidley
Austin LLP.

Cisco would like to thank them for reporting these issues to us.

Status of this Notice: FINAL
============================

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF
GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS
LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO
CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the
distribution URL in the following section is an uncontrolled copy, and may lack
important information or contain factual errors.

Distribution
============

This advisory is posted on Cisco's worldwide website at:

http://www.cisco.com/warp/public/707/cisco-sa-20061009-csd.shtml

In addition to worldwide web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail
and Usenet news recipients.

  * cust-security-announce at cisco.com
  * first-teams at first.org
  * bugtraq at securityfocus.com
  * vulnwatch at vulnwatch.org
  * cisco at spot.colorado.edu
  * cisco-nsp at puck.nether.net
  * full-disclosure at lists.grok.org.uk
  * comp.dcom.sys.cisco at newsgate.cisco.com

Future updates of this advisory, if any, will be placed on Cisco's worldwide
website, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the
above URL for any updates.

Revision History
================

+---------------------------------------------+
| Revision | 2006-October-09 | Initial public |
| 1.0      |                 | release.       |
+---------------------------------------------+

Cisco Security Procedures
=========================

Complete information on reporting security vulnerabilities in Cisco products,
obtaining assistance with security incidents, and registering to receive
security information from Cisco, is available on Cisco's worldwide website at
http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html.
This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at 
http://www.cisco.com/go/psirt.

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All contents are Copyright 1992-2006 Cisco Systems, Inc. All rights reserved.
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Updated: Oct 09, 2006                                        Document ID: 71723

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