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Cisco Security Advisory: Multiple Vulnerabilities in Cisco PIX and ASA Appliances
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Wed, 17 Oct 2007 13:15:25 -0400

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Cisco Security Advisory: Multiple Vulnerabilities in Cisco PIX and ASA
Appliances

Advisory ID: cisco-sa-20071017-asa

http://www.cisco.com/warp/public/707/cisco-sa-20071017-asa.shtml

Revision 1.0

For Public Release 2007 October 17 1600 UTC (GMT)

+--------------------------------------------------------------------

Summary
=======

Two crafted packet vulnerabilities exist in the Cisco PIX 500 Series
Security Appliance (PIX) and the Cisco 5500 Series Adaptive Security
Appliance (ASA) that may result in a reload of the device. These
vulnerabilities are triggered during processing of Media Gateway
Control Protocol (MGCP) packets, or during processing of Transport
Layer Security (TLS) traffic that terminates on the PIX or ASA security
appliance.

Note: These vulnerabilities are independent of each other; a device may
be affected by one and not by the other.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20071017-asa.shtml.

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

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

The Cisco PIX and ASA security appliances are affected by a crafted MGCP
packet vulnerability if MGCP application layer protocol inspection is
enabled and the device is running certain 7.x software versions. Version
6.3.x is not affected. MGCP inspection is not enabled by default. For
specific affected versions, refer to the "Software Versions and Fixes"
section.

The PIX and ASA security appliances are also affected by a crafted TLS
packet vulnerability that affects devices running certain 7.x software
versions if the software has one or more features configured that cause
TLS sessions to terminate on the PIX or ASA security appliance. These
functions include, but are not limited to, clientless WebVPN, HTTPS
management, cut-through proxy for network access, and TLS proxy for
encrypted voice inspection. Version 6.3.x is not affected. Features that
cause TLS sessions to terminate on the PIX and ASA security appliances
are not enabled by default. For specific affected versions, please refer
to the "Software Versions and Fixes" section.

In addition to the PIX and ASA security appliances,
the crafted MGCP packet vulnerability also affects the
Cisco Firewall Services Module (FWSM). More information
regarding the FWSM can be found in the companion advisory
http://www.cisco.com/warp/public/707/cisco-sa-20071017-fwsm.shtml.

To determine whether you are running a vulnerable version of Cisco PIX
or ASA software, issue the "show version" command-line interface (CLI)
command.

The following example shows a Cisco ASA Security Appliance that runs
software release 7.2(3):

    ASA# show version

    Cisco Adaptive Security Appliance Software Version 7.2(3)

    [...]

Customers who use the Cisco Adaptive Security Device Manager (ASDM) to
manage their devices can find the version of the software displayed in
the table in the login window or in the upper left corner of the ASDM
window. The version notation is similar to this:

    PIX Version 7.2(3)

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

With the exception of the FWSM, no other Cisco products are known to
be vulnerable to the issues described in this advisory.

Details
=======

This Security Advisory describes two distinct vulnerabilities that are
independent of each other.

1. Crafted MGCP Packet

A PIX or ASA security appliance with the Media Gateway Control Protocol
(MGCP) application layer protocol inspection feature enabled may reload
when the device processes a crafted MGCP packet. MGCP application layer
protocol inspection is not enabled by default.

MGCP messages are transmitted over the User Datagram Protocol (UDP),
which does allow the crafted MGCP messages to be sourced from a spoofed
address. Only the MGCP for gateway application (MGCP traffic on UDP port
2427) is affected.

To determine whether MGCP inspection is configured on the PIX or ASA,
log in to the device and issue the CLI command "show service-policy
| include mgcp". If the output contains the text "Inspect: mgcp" and
some statistics, then the device has a vulnerable configuration. The
following example shows a vulnerable Cisco ASA Security Appliance:

    ASA# show service-policy | include mgcp
          Inspect: mgcp, packet 15, drop 0, reset-drop 0
    ASA#

This vulnerability is documented in Cisco Bug ID CSCsi90468. The
corresponding Cisco Bug ID for the FWSM, included in the companion FWSM
Security Advisory, is CSCsi00694.

2. Crafted TLS Packet

Transport Layer Security (TLS) is the replacement for the Secure Socket
Layer (SSL) protocol. It is a protocol that provides, via cryptography,
secure communications between two end-points.

The PIX and ASA security appliances rely on TLS to protect the
confidentiality of communications in a variety of scenarios. In all
these scenarios, the PIX and ASA may be affected by a vulnerability in
the handling of the TLS protocol that may lead to a reload of the device
when it processes specially crafted TLS packets.

The scenarios affected by this vulnerability are clientless WebVPN
connections, HTTPS management sessions, cut-through proxy for network
access, and TLS proxy for encrypted voice inspection.

Clientless WebVPN Connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Clientless WebVPN connections are enabled via the "webvpn" command. For
example, the following configuration shows an ASA running 8.0 software
with clientless WebVPN configured and enabled. In this case the ASA will
listen for WebVPN connections on the default port, TCP port 443:

    http server enable
    !
    webvpn
     enable outside

Note that with this particular configuration, the device is vulnerable
to attacks coming from the outside interface.

HTTPS Management Sessions
~~~~~~~~~~~~~~~~~~~~~~~~~
HTTPS management sessions are enabled via the "http server enable" and
"http" commands. For example, the following configuration shows an ASA
configured for remote HTTPS management:

    http server enable
    http 192.168.0.0 255.255.255.0 inside

Note that with this particular configuration the device is vulnerable to
attacks coming from the *inside* interface and from the 192.168.0.0/ 24
IP sub-network.

Cut-Through Proxy for Network Access
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The cut-through proxy feature is used to authenticate users before
they can access the network. A configuration that requires users to
authenticate before they can be granted network access looks like the
following example:

    access-list auth-proxy extended permit tcp any any eq www
    access-list auth-proxy extended permit tcp any any eq telnet
    access-list auth-proxy extended permit tcp any any eq https
    !
    aaa authentication match auth-proxy inside LOCAL
    aaa authentication secure-http-client
    aaa authentication listener https inside port https

A configuration affected by this vulnerability will contain the command
"aaa authentication secure-http-client" or "aaa authentication listener
https inside port <port number>".

Note that with the particular configuration in the preceding example,
the device is vulnerable to attacks coming from the *inside* interface.

TLS Proxy for Encrypted Voice Inspection
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This feature allows the security appliance to decrypt, inspect and
modify (as needed, for example, performing NAT fixup), and re-encrypt
voice signaling traffic while all of the existing VoIP inspection
functions for Skinny and Session Initiation Protocol (SIP) protocols are
preserved. Once voice signaling is decrypted, the plain-text signaling
message is passed to the existing inspection engines. The security
appliance accomplishes this by acting as a TLS proxy between the IP
phone and Cisco Unified CallManager, which implies that TLS sessions are
terminating on the security appliance.

To determine whether the Cisco PIX or ASA security appliance is
configured to support inspection of encrypted voice, log in to the
device and issue the CLI command "show service-policy | include tls". If
the output contains the text "tls-proxy: active" and some statistics,
then the device has a vulnerable configuration. The following example
shows a vulnerable Cisco ASA Security Appliance:

    ASA# show service-policy | include tls
          Inspect: sip tls-proxy myproxy, packet 0, drop 0, reset-drop 0
                   tls-proxy: active sess 0, most sess 0, byte 0
          Inspect: skinny tls-proxy myproxy, packet 0, drop 0, reset-drop 0
                   tls-proxy: active sess 0, most sess 0, byte 0
    ASA#

This vulnerability is documented in Cisco Bug IDs CSCsg43276 and
CSCsh97120. This vulnerability does not affect the FWSM.

Vulnerability Scoring Details
+----------------------------

Cisco is providing scores for the vulnerabilities in this advisory based
on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in
this Security Advisory is done in accordance with CVSS version 2.0.

Cisco will provide a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of the
vulnerability in individual networks.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided an FAQ to answer additional questions regarding CVSS
at:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss.

Crafted MGCP packet causes PIX/ASA to reload (CSCsi90468)

CVSS Base Score - 7.1
    Access Vector -            Network
    Access Complexity -        Medium
    Authentication -           None
    Confidentiality Impact -   None
    Integrity Impact -         None
    Availability Impact -      Complete

CVSS Temporal Score - 5.9
    Exploitability -           Functional
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed


Crafted TLS packet causes PIX/ASA to reload (CSCsg43276 and CSCsh97120)

CVSS Base Score - 7.8
    Access Vector -            Network
    Access Complexity -        Low
    Authentication -           None
    Confidentiality Impact -   None
    Integrity Impact -         None
    Availability Impact -      Complete

CVSS Temporal Score - 6.4
    Exploitability -           Functional
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed

Impact
======

Successful exploitation of the vulnerabilities described in this
advisory will result in a reload of the affected device. Repeated
exploitation can result in a sustained denial of service (DoS)
condition.

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.

The following list contains the first fixed software release of each
vulnerability:

+---------------------------------------+
|               |  Affected  |  First   |
| Vulnerability |   Major    |  Fixed   |
|               |  Release   | Release  |
|---------------+------------+----------|
|               |            | 7.0      |
|               | 7.0        | (6.33)   |
|               |            | or later |
|               |------------+----------|
|               |            | 7.1      |
| Crafted MGCP  | 7.1        | (2.54)   |
| packet.       |            | or later |
|               |------------+----------|
|               |            | 7.2      |
|               | 7.2        | (2.23)   |
|               |            | or later |
|               |------------+----------|
|               | 8.0        | 8.0(2)   |
|---------------+------------+----------|
|               | 7.0        | Not      |
|               |            | Affected |
|               |------------+----------|
|               |            | 7.1      |
|               | 7.1        | (2.55)   |
| Crafted TLS   |            | or later |
|packet.        |------------+----------|
|               |            | 7.2      |
|               | 7.2        | (2.24)   |
|               |            | or later |
|               |------------+----------|
|               | 8.0        | Not      |
|               |            | Affected |
+---------------------------------------+

The following maintenance software releases are the first software
releases that contain the fixes for the two vulnerabilities mentioned in
this Security Advisory: 7.0(7), 7.1(3), 7.2(3), and 8.0(2).

Fixed PIX software can be downloaded from
http://www.cisco.com/pcgi-bin/tablebuild.pl/pix?psrtdcat20e2.

Fix ASA software can be downloaded from
http://www.cisco.com/pcgi-bin/tablebuild.pl/asa?psrtdcat20e2.

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

General Considerations
+---------------------

Filters that deny TLS packets using TCP port 443 and MGCP packets on UDP
port 2427 should be deployed throughout the network as part of a transit
ACL (tACL) policy for protection of traffic which enters the network at
ingress access points. This policy should be configured to protect the
network device where the filter is applied and other devices behind it.
Filters for TLS packets using TCP port 443 and MGCP packets on UDP port
2427 should also be deployed in front of vulnerable network devices so
that traffic is only allowed from trusted clients.

Additional information about tACLs is available in "Transit Access
Control Lists : Filtering at Your Edge":

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801afc76.shtml.

Additional mitigations techniques that can be deployed on Cisco devices
within the network are available in the Cisco Applied Intelligence
companion document for this advisory:

http://www.cisco.com/warp/public/707/cisco-air-20071017-asafwsm.shtml.

1. Crafted MGCP Packet

There is no workaround for this vulnerability other than disabling MGCP
application layer protocol inspection on the device.

Leveraging anti-spoofing techniques will help mitigate spoofed packets
from triggering this vulnerability.

Limiting MGCP application layer inspection to traffic between MGCP
gateways may help to mitigate this vulnerability since it would require
an attacker to have additional information (the addresses of the MGCP
gateways) to launch a successful attack. To limit MGCP application layer
inspection to traffic between certain devices, a class map that matches
only traffic between the gateways must be created. Then, MGCP inspection
must be performed on traffic in that class. The following example shows
how to accomplish this:

    ASA(config)# access-list mgcp_traffic permit udp host 192.168.0.1
        host 172.16.0.1 eq 2427
    ASA(config)# access-list mgcp_traffic permit udp host 172.16.0.1
        host 192.168.0.1 eq 2427
    ASA(config)# class-map MGCP
    ASA(config-cmap)# match access-list mgcp_traffic
    ASA(config-cmap)# exit
    ASA(config)# policy-map global_policy
    ASA(config-pmap)# class inspection_default
    ASA(config-pmap-c)# no inspect mgcp
    ASA(config-pmap-c)# exit
    ASA(config-pmap)# class MGCP
    ASA(config-pmap-c)# inspect mgcp
    ASA(config-pmap-c)# exit
    ASA(config-pmap)# exit
    ASA(config)#

Note that MGCP inspection is applied only to UDP traffic between hosts
192.168.0.1 and 172.16.0.1

See the Cisco Applied Intelligence companion document for additional
mitigation possibilities.

2. Crafted TLS Packet

ASDM is used to manage the Cisco PIX or ASA security appliance. Access
to ASDM should be allowed only on trusted interfaces and only from
authorized hosts. Restricting ASDM access to trusted hosts limits the
ability of an attacker to conduct these attacks.

For example, to limit ASDM access to a single host on the inside
interface with an address of 192.168.1.2, enter the following command:

    hostname(config)# http 192.168.1.2 255.255.255.255 inside

Additional information is available at:

Cisco Security Appliance Command Line Configuration Guide, Version 7.2
(http://www.cisco.com/en/US/docs/security/asa/asa72/configuration/guide/mgaccess.html#wp1047288)

There are no workarounds if the clientless WebVPN, cut-through proxy for
network access, and TLS proxy for encrypted voice inspection features
are in use.

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

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 vulnerabilities described in this advisory.

These vulnerabilities were discovered by Cisco internal testing and
customer service requests.

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-20071017-asa.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      | 2007-October-17 | 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 2006-2007 Cisco Systems, Inc. All rights
reserved.
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Updated: Oct 17, 2007                              Document ID: 98711

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