Cisco Security Advisory
Limitations in Cisco Secure Desktop
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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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20061009-csd.
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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.
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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:
Inability to Detect Hardware Keystroke Loggers
There are no workarounds for the inability to detect hardware keyloggers.
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There are no fixes for the limitations described in this advisory.
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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.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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