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Cisco Security Advisory: Cisco 7600 Series Router Session Border
                         Controller Denial of Service Vulnerability

Document ID: 109483

Advisory ID: cisco-sa-20090304-sbc

http://www.cisco.com/warp/public/707/cisco-sa-20090304-sbc.shtml 

Revision 1.0

For Public Release 2009 March 4 1600 UTC (GMT)

- ---------------------------------------------------------------------

Summary
======
A denial of service (DoS) vulnerability exists in the Cisco Session
Border Controller (SBC) for the Cisco 7600 series routers. Cisco has
released free software updates that address this vulnerability.
Workarounds that mitigate this vulnerability are available.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20090304-sbc.shtml 

Affected Products
================
Vulnerable Products
+------------------

All Cisco ACE-based SBC modules running software versions prior to
3.0(2) are affected.

To determine the version of the Cisco SBC software running on a
system, log in to the device and issue the show version command to
display the system banner.

    card_A/Admin# show version
      system image file: [LCP] disk0:c76-sbck9-mzg.3.0.1_AS3_0_00.bin
    



Cisco SBC software version 3.0.1 is running in the device used in
this example.

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

The Cisco XR 12000 Series SBC is not vulnerable. Additionally, the
Cisco ACE Module, Cisco ACE 4710 Application Control Engine, Cisco
ACE XML Gateway, Cisco ACE Web Application Firewall, and the Cisco
ACE GSS (Global Site Selector) 4400 Series are not affected by this
vulnerability. No other Cisco products are currently known to be
affected by this vulnerability.

Details
======
The Session Border Controller (SBC) enables direct IP-to-IP
interconnect between multiple administrative domains for
session-based services providing protocol interworking, security, and
admission control and management. The SBC is a multimedia device that
sits on the border of a network and controls call admission to that
network. A vulnerability exists in the Cisco SBC where an
unauthenticated attacker may cause the Cisco SBC card to reload by
sending crafted TCP packets over port 2000. Repeated exploitation
could result in a sustained DoS condition.

Note: Only the Cisco SBC module reloads after successful
exploitation. The Cisco 7600 series router does not reload and it is
not affected by this vulnerability.

Note: TCP port 2000 is typically used by Skinny Call Control Protocol
(SCCP) applications. However, the Cisco SBC module uses TCP port 2000
for high availability (redundancy) communication, but does not use
the SCCP for this purpose.

This vulnerability is documented in Cisco Bug IDs CSCsq18958 (
registered customers only) ; and has been assigned the Common
Vulnerability and Exposures (CVE) IDs CVE-2009-0619.

Vulnerability Scoring Details
============================
Cisco has provided scores for the vulnerability 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.

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

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

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 

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 vulnerability may cause a reload of
the affected device. Repeated exploitation could result in a
sustained DoS condition.

Software Versions and Fixes
==========================
This vulnerability has been corrected in Cisco SBC software release
3.0(2).

Cisco SBC software can be downloaded from:

http://www.cisco.com/pcgi-bin/tablebuild.pl/sbc-7600-crypto 

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.

Workarounds
==========
As a workaround, configure an access control list (ACL) in the
signaling / media VLAN on the Route Processor (RP). The following
examples show how VLAN 140 is configured as the signaling / media
VLAN. A separate VLAN (VLAN 77) is configured as Fault Tolerance
(FT). An ACL is added to the signaling/media VLAN on the RP filtering
all TCP port 2000 packets to the alias IP address.

Cisco SBC configuration

    interface vlan 140
      ip address 10.140.1.90 255.255.255.0
      alias 10.140.1.100 255.255.255.0
      peer ip address 10.140.1.8 255.255.255.0
    !
    ft interface vlan 77
      ip address 192.168.1.1 255.255.255.0
      peer ip address 192.168.1. 255.255.255.0


RP Configuration

    !- ACL blocking all TCP port 2000 traffic to the 10.140.1.0 internal network
    !
    access-list 100 deny   tcp any host 10.140.1.100 eq 2000
    access-list 100 permit ip any any
    !
    interface Vlan140
     ip address 10.140.1.1 255.255.255.0
    !- ACL is applied to the VLAN interface to egress traffic
      ip access-group 100 out
    !

The alias command under VLAN 140 is configured with an IP address
that floats between active and standby modules when using high
availability. Only TCP port 2000 traffic destined to this IP address
may trigger this vulnerability. An access control list (ACL) is
configured to deny TCP port 2000 destined to the alias IP address
(10.140.1.100). The ACL is applied egress in the RP.

Note: TCP port 2000 is used by Skinny Call Control Protocol (SCCP)
applications; however, in this case it is used by the SBC for
internal communications. The previous ACL only blocks TCP port 2000
traffic to the alias IP address. TCP port 2000 is not used by the
alias IP address. This ACL should not cause any collateral damage.

Additional mitigations 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-amb-20090304-sbc.shtml 

Obtaining Fixed Software
=======================
Cisco has released free software updates that address this
vulnerability. 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/en/US/products/prod_warranties_item09186a008088e31f.html 
or as otherwise set forth at Cisco.com Downloads at 
http://www.cisco.com/public/sw-center/sw-usingswc.shtml 

Do not contact 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 agreements 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 do not hold a Cisco
service contract, and customers who purchase through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should acquire 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 

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

Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html 
for additional TAC contact information, including 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 found during internal testing.

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-20090304-sbc.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-bulletins@lists.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      | 2009-March-04 | 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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