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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-20
071017-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-2
0071017-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/in
telligence/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/c
vss.
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?psr
tdcat20e2.
Fix ASA software can be downloaded from
http://www.cisco.com/pcgi-bin/tablebuild.pl/asa?psr
tdcat20e2.
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_paper09186a00801af
c76.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.c
om/en/US/docs/security/asa/asa72/configuration/guide/mgacces
s.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-alertcisco.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: taccisco.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-20
071017-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-announcecisco.com
* first-teamsfirst.org
* bugtraqsecurityfocus.com
* vulnwatchvulnwatch.org
* ciscospot.colorado.edu
* cisco-nsppuck.nether.net
* full-disclosurelists.grok.org.uk
* comp.dcom.sys.cisconewsgate.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/produ
cts/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/g
o/psirt.
+-----------------------------------------------------------
---------
All contents are Copyright 2006-2007 Cisco Systems, Inc. All
rights
reserved.
+-----------------------------------------------------------
---------
Updated: Oct 17, 2007 Document
ID: 98711
+-----------------------------------------------------------
---------
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