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Cisco Security Advisory: 
Cisco VPN 3000 Concentrator FTP Management Vulnerabilities

Document ID: 71141

Advisory ID: cisco-sa-20060823-vpn3k

http://www.cisco.com/warp/public/707/cisco-sa-20060823-vpn3k.shtml

Revision 1.0

For Public Release 2006 August 23 1600 UTC (GMT)

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Contents
========

    Summary
    Affected Products
    Details
    Impact
    Software Versions and Fixes
    Workarounds
    Obtaining Fixed Software
    Exploitation and Public Announcements
    Status of This Notice: FINAL
    Distribution
    Revision History
    Cisco Security Procedures

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Summary
=======

The Cisco VPN 3000 series concentrators are affected by two
vulnerabilities when file management via File Transfer Protocol (FTP)
is enabled that could allow authenticated or unauthenticated attackers
to execute certain FTP commands and delete files on the concentrator.

None of the vulnerabilities allows unauthorized users to transfer files
from or to the concentrator.

Cisco has made free software available to address these vulnerabilities
for affected customers. There are workarounds available to mitigate
these vulnerabilities as well.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20060823-vpn3k.shtml.

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

Vulnerable Products
+------------------

Cisco VPN 3000 series concentrators 3005, 3015, 3020, 3030, 3060, and
the 3080 are affected by these vulnerabilities if they are running a
vulnerable software version and if the concentrator is configured to
use FTP as a management protocol. FTP as a management protocol is
enabled by default.

Vulnerable software versions are:

  * Any version prior to 4.1
  * Any 4.1.x version prior to, and including, 4.1(7)L
  * Any 4.7.x version prior to, and including, 4.7(2)F

There are two ways to determine whether the FTP protocol is enabled as
a file management protocol: using the web Graphical User Interface
(GUI), or using a Command-Line Interface (CLI) via a console, telnet,
or Secure Shell (SSH) connection.

To use the GUI to determine whether the FTP protocol is enabled as a
file management protocol, connect to the web administration interface
of the concentrator via the URL:

https://<IP address of concentrator>/admin/

Then log in to the concentrator using the device administrator
credentials and go to the screen "Configuration | System | Management
Protocols | FTP". This screen will indicate whether the FTP server on
the concentrator is enabled.

To accomplish the same thing using the CLI, log in to the concentrator
using the chosen access method (console, Telnet or SSH) and go to the
same screen ("Configuration -> System Management -> Management
Protocols -> Configure FTP"). The prompt will indicate with a number
whether the FTP server is enabled.

Products Confirmed Not Vulnerable
+--------------------------------

The Cisco VPN 3002 Hardware Client is not affected by these
vulnerabilities.

Please note that Cisco VPN 3000 Series concentrators are not affected
by these vulnerabilities if FTP is not configured as a management
protocol.

No other Cisco products are currently known to be affected by these
vulnerabilities.

Details
=======

The Cisco VPN 3000 series concentrators are a family of purpose-built,
remote access Virtual Private Network (VPN) platforms for data
encryption and authentication.

The File Transfer Protocol is an application-layer protocol that allows
transfer of files between TCP/IP hosts. It uses Transmission Control
Protocol (TCP) as the transport protocol and supports user
authentication.

The Cisco VPN 3000 series concentrators can be configured to use the
FTP protocol to manage files stored on the concentrator, like
configuration files and certificates. Files can be uploaded to, or
downloaded from, the concentrator for backup and configuration
purposes.

Two vulnerabilities affect the Cisco VPN 3000 series concentrators when
FTP is enabled as a file management protocol. By exploiting these
vulnerabilities, an attacker could execute the following FTP commands:

  * CWD - Change working directory
  * MKD - Create (make) a directory
  * CDUP - Change directory to the directory one level up
  * RNFR - Rename file
  * SIZE - Get file size
  * RMD - Remove directory

These vulnerabilities are documented in Cisco Bug IDs CSCse10733 
and CSCse10753.

None of these vulnerabilities allows unauthorized users to download or
upload files from/to the concentrator.

Impact
======

Successful exploitation of these vulnerabilities may allow an attacker
to:

  * Perform network reconnaissance via the "CWD", "CDUP", and "SIZE" FTP
    commands.
  * Change the configuration of the concentrator by renaming or
    deleting configuration and certificate files via the "RNFR" and "RMD"
    FTP commands.

Please note that since none of these vulnerabilities allows an attacker
to upload or download files to/from the concentrator, it is not
possible to obtain the configuration of a device or to upload a
modified configuration by exploiting the vulnerabilities.

Software Versions and Fixes
===========================

When considering software upgrades, also consult 
http://www.cisco.com/go/psirt and any subsequent advisories to 
determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the
devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported
properly by the new release. If the information is not clear, contact
the Cisco Technical Assistance Center ("TAC") or your contracted
maintenance provider for assistance.

Both vulnerabilities are fixed in versions 4.1(7)M and 4.7(2)G of the
VPN 3000 Series Concentrators software.

Fixed versions of the Cisco VPN 3000 Series concentrators software can
be downloaded from the following location:

http://www.cisco.com/pcgi-bin/tablebuild.pl/vpn3000-3des 

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

Disabling FTP
+------------

If FTP is not needed to manage the VPN 3000 concentrator, network
security best practices recommend that it be disabled. This will
completely eliminate the vulnerability. Secure alternatives to FTP
include Secure Hyper-Text Transfer Protocol (HTTPS) and Secure Copy
(SCP) via Secure Shell (SSH).

The use of FTP as a management protocol can be disabled by connecting
to the web administration interface of the concentrator via the URL:

https://<IP address of concentrator>/admin/

and then logging in to the concentrator using the device administrator
credentials, going to the screen "Configuration | System | Management
Protocols | FTP", and unchecking the "Enable" checkbox.

Limiting FTP Access
+------------------

It is possible to limit the exposure of the concentrator by permitting
remote FTP management connections only from known, trusted IP
addresses. This is also considered a network security best practice.

Limiting FTP access to specific IP addresses can be accomplished on the
VPN 3000 Series concentrators by defining rules and filters. The
traffic filters can be mapped to the interfaces, LAN-to-LAN tunnels,
and VPN groups. Traffic rules and filters are configured via the GUI in
the screen "Configuration | Policy Management | Traffic Management".

To allow FTP access only from specific IP addresses, at least two
traffic rules must be defined. The first rule would permit FTP traffic
from a specific, trusted IP address or IP subnet. The second rule would
deny all other FTP traffic directed at the private interface.

The parameters of the first rule could be:

  * Rule Name: permit_ftp_in
  * Direction: Inbound
  * Action: Forward
  * Protocol: TCP
  * Source Address/Wildcard-mask: <Allowed IP address range>
  * Destination Address/Wildcard-mask: <IP address of private
    interface>/0.0.0.0
  * TCP/UDP Source Port: Range, from 0 to 65535
  * TCP/UDP Destination Port: FTP (21)

This rule will permit inbound TCP port 21 (FTP) traffic but only when
the traffic originates from a specific IP address range.

The parameters of the second rule could be:

  * Rule Name: deny_ftp_in
  * Direction: Inbound
  * Action: Drop and Log
  * Protocol: TCP
  * Source Address/Wildcard-mask: 0.0.0.0/255.255.255.255
  * Destination Address/Wildcard-mask: <IP address of private
    interface>/0.0.0.0
  * TCP/UDP Source Port: Range, from 0 to 65535
  * TCP/UDP Destination Port: FTP (21)

This rule will drop and log all inbound TCP port 21 (FTP) traffic that
is directed at the IP address of the private interface.

Note:  When new rules are added to a filter, the new rules get added at
the bottom of the list of existing rules in the filter. The
concentrator processes rules in a filter in sequential order, so if at
the bottom of the list there is a rule that permits all traffic (which
is the case with the predefined "Private" filter applied by default to
the Private interface), then the new rules will not be executed. For
this reason it is important that the new rules intended to allow FTP
traffic only from trusted addresses be moved to the top of the list of
rules.

When the traffic rules have been created, they need to be added to a
filter by going to the GUI screen "Configuration | Policy Management |
Traffic Management | Filters", selecting the desired filter from the
list, clicking on the "Assign Rules to Filter" button, and then
selecting the new filter rules and clicking on the "<< Add" button.

To completely protect the VPN 3000 concentrator from unauthorized FTP
traffic, the filter with the new traffic rules needs to be applied to
the following:

  * Interfaces: a filter is applied to an interface by going to the GUI
    screen "Configuration | Interfaces", clicking on an interface name,
    and then selecting a filter in the "General" tab.

    By default the predefined filter "Private" is applied to the
    Private interface and the predefined filter "Public" is applied to
    the "Public" interface. The "Private" filter is very permissive and
    it is recommended that the above rules to limit FTP management
    traffic be added to this filter. The "Public" filter does not
    permit FTP traffic by default, and if changes have been made to
    permit FTP traffic, it is recommended that rules are added to only
    permit FTP traffic to the concentrator from specific IP addresses,
    as described above.

  * LAN-to-LAN tunnels: a filter is applied to a LAN-to-LAN tunnel by
    going to the GUI screen "Configuration | Tunneling and Security |
    IPSec | LAN-to-LAN", selecting the LAN-to-LAN connection and
    clicking the "Modify" button, and then selecting the specific
    filter in the "Modify an IPSec LAN-to-LAN connection" screen. By
    default a LAN-to-LAN connection does not have any filter applied to
    it.

  * Remove Access VPN tunnels: a filter is applied to a remote access
    VPN group by going to the GUI screen "Configuration | User
    Management | Groups", selecting the VPN group and clicking the
    "Modify Group" button, and then selecting the specific filter in
    the "General" tab of the "Modify Group" screen. By default a VPN
    group does not have any filter applied to it.

By adding these two traffic rules to the filter applied to the an
interface, LAN-to-LAN tunnel, and VPN group, the FTP traffic directed
at the concentrator will only be allowed from the specific, trusted IP
addresses, regardless of where the IP addresses are located, i.e.
internal network or across a VPN tunnel. FTP traffic directed at the
concentrator from anywhere else will be dropped and logged. All other
FTP traffic is not affected by these rules.

If you do not wish to define multiple filters for each interface and
the VPN tunnels, you can add the two traffic rules described above to
the default "Private" filter and then apply this filter to the Private
interface as well as to any LAN-to-LAN connections and Remote Access
VPN groups.

Please note that using the "Access Control List" feature
("Administration | Access Rights | Access Control List") to control FTP
access will not protect against these vulnerabilities because the check
for valid IP addresses takes place at authentication time, and the
actual vulnerability described in this document takes place before
authentication.

In addition to the access control mechanism that can be implemented on
the VPN 3000 concentrator itself, FTP access to the VPN 3000
concentrator could be blocked as part of an Infrastructure Access
Control List (ACL) on screening routers, switches and firewalls
controlling all access to the trusted network. Infrastructure ACLs are
considered a network security best practice and should be considered as
a long-term addition to good network security, as well as a workaround
for this specific vulnerability. The white paper entitled "Protecting
Your Core: Infrastructure Protection Access Control Lists" presents
guidelines and recommended deployment techniques:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a1a55.shtml

Backing Up Configuration and Certificates
+----------------------------------------

Always keep backup copies, outside of the concentrator's file system,
of the concentrator's configuration and certificates.

Management of configuration files can be done from the GUI screen
"Administration | File Management". Please refer to the "File
Management" section of the VPN 3000 Series Concentrator Reference,
Volume II, for additional information:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_administration_guide_chapter09186a00803ef263.html

Management of certificates can be done from the GUI screen
"Administration | Certificate Management". Please refer to the
"Certificate Management" section of the VPN 3000 Series Concentrator
Reference, Volume II, for additional information:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_administration_guide_chapter09186a00803ef352.html

Obtaining Fixed Software
========================

Cisco has made free software available to address this vulnerability
for affected customers. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they
have purchased. By installing, downloading, accessing or otherwise
using such software upgrades, customers agree to be bound by the terms
of Cisco's software license terms found at 
http://www.cisco.com/public/sw-license-agreement.html, or as otherwise 
set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.

Customers with Service Contracts
+-------------------------------

Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on Cisco's worldwide
website at http://www.cisco.com.

Customers using Third-party Support Organizations
+------------------------------------------------

Customers whose Cisco products are provided or maintained through prior
or existing agreement with third-party support organizations such as
Cisco Partners, authorized resellers, or service providers should
contact that support organization for guidance and assistance with the
appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or
fix is the most appropriate for use in the intended network before it
is deployed.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
  * e-mail: tac@cisco.com

Have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
for additional TAC contact information, including special localized
telephone numbers and instructions and e-mail addresses for use in
various languages.

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

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

This vulnerability was reported to Cisco by the NCC Group 
(http://www.nccgroup.com.) Cisco would like to thank the NCC Group for
reporting this vulnerability and working with us towards resolution of
this problem.

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-20060823-vpn3k.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@cisco.com
  * first-teams@first.org
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.grok.org.uk
  * comp.dcom.sys.cisco@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 |                | Initial    |
| 1.0      | 2006-August-23 | public     |
|          |                | 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. Important Notices and Privacy Statement.

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Updated: Aug 23, 2006                                Document ID: 71141

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