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Cisco Security Advisory: Multiple Vulnerabilities in Firewall Services Module
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Wed, 17 Oct 2007 12:29:47 -0400

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Cisco Security Advisory: Multiple Vulnerabilities in Firewall Services
Module

Advisory ID: cisco-sa-20071017-fwsm

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

Revision 1.0

For Public Release 2007 October 17 1600 UTC (GMT)

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

Summary
=======

Two crafted packet vulnerabilities exist in the Cisco Firewall
Services Module (FWSM) that may result in a reload of the FWSM. These
vulnerabilities can be triggered during the processing of HTTPS
requests, or during the processing of Media Gateway Control Protocol
(MGCP) packets.

A third vulnerability may cause access control list (ACL) entries to not
be evaluated after the access list has been manipulated.

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

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

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

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

The FWSM is affected by a crafted HTTPS request vulnerability if the
HTTPS server on the FWSM is enabled and is running software versions
3.1(5) and prior or 3.2(1). Version 2.3.x is not affected. The HTTPS
server is not enabled by default.

The FWSM is affected by a crafted MGCP packet vulnerability if MGCP
application layer protocol inspection is enabled and the device is
running software version 3.1(5) and prior. Versions 2.3.x and 3.2.x are
not affected. MGCP inspection is not enabled by default.

The FWSM is affected by an access control list corruption vulnerability
that may result in the ACL not working properly, i.e. the ACL may allow
traffic that would normally be denied, or would deny traffic that would
normally be permitted. Affected versions include 3.1(6) and prior and
3.2(2) and prior. Version 2.3.x is not affected.

In addition to the FWSM, the crafted MGCP packet vulnerability
also affects the PIX 500 Series Security Appliances and the
Cisco ASA 5500 Series Adaptive Security Appliances. More
information regarding vulnerabilities affecting the PIX
and ASA can be found in the companion advisory located at
http://www.cisco.com/warp/public/707/cisco-sa-20071017-asa.shtml.

To determine if you are running a vulnerable version of FWSM software,
issue the "show module" command-line interface (CLI) command from
Cisco IOS or Cisco CatOS to identify what modules and sub-modules are
installed in the system.

The following example shows a system with a Firewall Service Module
(WS-SVC-FWM-1) installed in slot 4.

switch#show module
 Mod Ports Card Type                              Model              Serial No.
 --- ----- -------------------------------------- ----------------- -----------
 1   48    SFM-capable 48 port 10/100/1000mb RJ45 WS-X6548-GE-TX    SAxxxxxxxxx
 4    6    Firewall Module                        WS-SVC-FWM-1      SAxxxxxxxxx
 5    2    Supervisor Engine 720 (Active)         WS-SUP720-BASE    SAxxxxxxxxx
 6    2    Supervisor Engine 720 (Hot)            WS-SUP720-BASE    SAxxxxxxxxx

After locating the correct slot, issue the "show module <slot number>"
command to identify the software version that is running:

switch#show module 4
 Mod Ports Card Type                              Model              Serial No.
 --- ----- -------------------------------------- ----------------- -----------
 4    6    Firewall Module                        WS-SVC-FWM-1      SAxxxxxxxxx

 Mod MAC addresses                     Hw     Fw           Sw           Status
 --- --------------------------------- ------ ------------ ------------ -------
 4   0003.e4xx.xxxx to 0003.e4xx.xxxx  3.0    7.2(1)       3.1(3)       Ok

The example above shows that the FWSM is running version 3.1(3) as
indicated by the column under "Sw" above.

Note: Recent versions of Cisco IOS will show the software version of
each module in the output from the "show module" command; therefore,
executing the "show module <slot number>" command is not necessary.

Alternatively, the information may also be obtained directly from the
FWSM through the "show version" command as seen below.

    FWSM#show version
    FWSM Firewall Version 3.1(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:

    FWSM Version: 3.1(3)

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

With the exception of the Cisco PIX 500 Series Security Appliances and
the Cisco ASA 5500 Series Adaptive Security Appliances, no other Cisco
products are known to be vulnerable to the issues described in this
advisory.

Details
=======

This Security Advisory describes multiple distinct vulnerabilities.
These vulnerabilities are independent of each other.

1. Crafted HTTPS Request

A FWSM that has the HTTPS server enabled may reload if a crafted HTTP
request is processed by the device. The HTTPS server is disabled by
default.

The source IP address and interface on which the HTTPS request is
received must comply with the configured "http <source IP> <address
mask> <source interface>" command. For example, if the command "http
10.10.10.0 255.255.255.0" inside is present in the configuration, then
only crafted HTTPS requests coming from the 10.10.10.0/24 network may
represent an issue for the device.

No other HTTP(s) services are known to be affected, such as HTTP
Inspection, HTTP/HTTPS Proxy Server, and HTTP redirect.

To confirm if the HTTPS server is enabled, log in to the FWSM and issue
the CLI command "show running-config | include http". If the output
contains both "http server enable" and "http <source IP> <address mask>
<source interface>", then the device has a vulnerable configuration. The
following example shows an FWSM with a vulnerable configuration:

    FWSM# show running-config | include http
    http server enable
    http 10.10.10.0 255.255.255.0 inside
    FWSM#

This vulnerability is documented in Cisco Bug ID CSCsi77844 and does not
affect the PIX or ASA security appliances.

2. Crafted MGCP Packet

An FWSM that has the MGCP application layer protocol inspection feature
enabled may reload when a crafted MGCP packet is processed by the
device. 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 FWSM, 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 FWSM:

    FWSM# show service-policy | include mgcp
          Inspect: mgcp, packet 66, drop 0, reset-drop 0
    FWSM#

This vulnerability is documented in Cisco Bug ID CSCsi00694. The
corresponding Cisco Bug ID for the PIX and ASA security appliances,
included in the companion PIX/ASA Security Advisory, is CSCsi90468.

3. Manipulation of ACL May Cause ACL Corruption

This vulnerability may cause access control list entries (ACEs) in an
ACL that has been manipulated to not be evaluated. Manipulation of the
ACL can take place via the command-line interface or ASDM and consists
of deleting and re-adding ACEs. When the access list is manipulated
in this way, the internal structure that represents the ACL becomes
corrupted, resulting in the FWSM not evaluating some ACEs.

Because ACEs in an ACL may not be evaluated, the ACL may allow traffic
that would normally be denied, or deny traffic that would normally be
permitted.

This vulnerability is documented in Cisco Bug ID CSCsj52536 and does not
affect the PIX or ASA security appliances.

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 HTTPS Request (CSCsi77844)

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

* Crafted MGCP packet (CSCsi00694)

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

* Manipulation of ACL May Cause ACL Corruption (CSCsj52536)

CVSS Base Score - 6.8
    Access Vector -            Network
    Access Complexity -        Medium
    Authentication -           None
    Confidentiality Impact -   Partial
    Integrity Impact -         Partial
    Availability Impact -      Partial

CVSS Temporal Score - 5.6
    Exploitability -           Functional
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed

Impact
======

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

In the case of the "Manipulation of ACL May Cause ACL Corruption"
vulnerability, a device that becomes affected after an administrator
manipulates an ACL may allow traffic that would normally be denied,
or deny traffic that would normally be permitted. If the ACL is used
for other functions like NAT (policy NAT and NAT exemption), AAA
(auth-proxy), control of access to the device (SSH, Telnet, HTTP, ICMP),
then those functions may be adversely affected as well.

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 that
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 for each
vulnerability:

+---------------------------------------+
|               | Affected |   First    |
| Vulnerability |  Major   |   Fixed    |
|               | Release  |  Release   |
|---------------+----------+------------|
|               | 2.3      | Not        |
|               |          | affected   |
|Crafted HTTPS  |----------+------------|
| Request       | 3.1      | 3.1(6)     |
|               |----------+------------|
|               | 3.2      | 3.2(2)     |
|---------------+----------+------------|
|               | 2.3      | Not        |
|               |          | affected   |
|Crafted MGCP   |----------+------------|
| packet        | 3.1      | 3.1(6)     |
|               |----------+------------|
|               | 3.2      | Not        |
|               |          | affected   |
|---------------+----------+------------|
|               | 2.3      | Not        |
|               |          | affected   |
|               |----------+------------|
| Manipulation  | 3.1      | 3.1(7)     |
|of ACL May     |----------+------------|
| Cause ACL     |          | 3.2(3),    |
| Corruption    |          | available  |
|               | 3.2      | week of    |
|               |          | October    |
|               |          | 22, 2007   |
+---------------------------------------+

FWSM software versions 3.1(7) and 3.2(3) contain the fixes for all the
vulnerabilities described in this document.

FWSM software is available for download
from the following location on cisco.com:
http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-fwsm?psrtdcat20e2.

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

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

Filters that deny HTTPS 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 HTTPS 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 HTTPS Request

There are no workarounds for these vulnerabilities other than disabling
the HTTPS server on the device. See the Cisco Applied Intelligence
companion document for mitigations.

Limiting the networks and hosts that can connect to the HTTPS server
on the FWSM can help mitigate this vulnerability. For example, if
the command "http 10.10.10.0 255.255.255.0 inside" is present in the
configuration, then only hosts on this trusted network can establish
HTTPS sessions with the FWSM. This scenario eliminates the possibility
of malicious hosts on other IP networks launching successful attacks
against the FWSM.

2. 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:

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

3. Manipulation of ACL May Cause ACL Corruption

A possible workaround for this vulnerability is to completely remove the
ACL before modifying it, and then recreate it with the desired changes.
ACLs can be removed with the command "clear configure access-list <ACL
name>".

Note: The ACL corruption does not occur during normal operation of the
device, and it cannot be triggered by some type of traffic. It can
only occur if an administrator makes configuration changes, and more
specifically, if an administrator manipulates an ACL. For this reason,
if ACL changes are made only during a maintenance window and the FWSM is
reloaded after making those changes, there should not be any concerns
with this vulnerability.

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.

The crafted packet vulnerabilities were discovered by Cisco during
internal testing of the associated products.

The ACL corruption vulnerability was discovered during the resolution of
customer support cases.

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-fwsm.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.
+--------------------------------------------------------------------

Updated: Oct 17, 2007                              Document ID: 98612

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