Products & Services

Contents

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

Vulnerable Products

Products Confirmed Not Vulnerable

SIP is a protocol designed for use in IP voice networks and is widely used for Voice over Internet Protocol (VoIP) communications worldwide.

Cisco devices running certain versions of IOS with support for SIP services may be affected by a vulnerability that leads to a reload of the device with a crafted series of SIP packets to either TCP port 5060 or UDP port 5060. This vulnerability affects routers that contain any SIP configuration, including SIP gateways. This issue is being tracked as Cisco Bug ID CSCsh58082 ( registered customers only) .

In addition, certain versions of IOS with support for SIP services may process SIP messages even if they are not configured for SIP operation. To process SIP messages IOS will open UDP port 5060 and TCP port 5060 for listening. The Cisco Bug ID that documents the issue of IOS processing SIP messages without being configured for SIP operation is CSCsb25337 ( registered customers only) . The fix for this bug turns off the listening ports TCP 5060 and UDP 5060.

A device must have an open SIP port to be vulnerable to this issue. Devices which do not listen on TCP 5060 or UDP 5060 are not vulnerable. Because SIP utilizes UDP as a transport, it is possible to spoof the sender's IP address, which may defeat ACLs that permit communication to these ports from trusted IP addresses.

Vulnerability Scoring Details

Cisco is providing scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).

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.

Cisco PSIRT will set the bias in all cases to normal. Customers are encouraged to apply the bias parameter when determining the environmental impact of a particular vulnerability.

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.

CSCsb25337 ( registered customers only) causes processing of SIP messages to occur even when an IOS device is not configured for correct SIP operation. The scoring of this bug has been done taking in consideration the potential for reconnaissance since this bug, by itself, has no potential for denial-of-service.

Successful exploitation of the vulnerability may result in a reload of the device. The issue may be repeatedly exploited, leading to an extended Denial Of Service (DoS) condition.

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.

Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild" and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).

For more information on the terms "Rebuild" and "Maintenance," consult the following URL: http://www.cisco.com/warp/public/620/1.html.

The following table is written to indicate the vulnerable and fixed status of CSCsh58082 ( registered customers only) , which is the bug responsible for the device reload. This table also contains information about IOS releases that are fixed for CSCsb25337 ( registered customers only) , which turns off processing of SIP messages when the device is not fully configured for SIP operation. At the time of the 2.0 publishing, there are no fixes for CSCsh58082 ( registered customers only) .

Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory: http://www.cisco.com/warp/public/707/cisco-amb-20070131-sip.shtml.

Disable SIP listening ports

For devices which do not require SIP to be enabled, the simplest and most effective workaround is to disable SIP processing on the device with the following commands.

Warning: When applying this workaround to devices which are processing MGCP or H.323 calls, the device will not allow you to stop SIP processing while active calls are being processed. Under these circumstances, this workaround should be implemented during a maintenance window when active calls can be briefly stopped.

Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#sip-ua
Router(config-sip-ua)#no transport udp
Router(config-sip-ua)#no transport tcp
Router(config-sip-ua)#end

After applying this workaround the commands show ip sockets and show tcp brief all will not show the device listening on UDP and TCP port 5060:

Router#show ip sockets
Proto    Remote      Port      Local       Port  In Out Stat TTY
 17   --listen--          9.13.32.18       2887   0   0   11   0

Router#show tcp brief all
TCB       Local Address           Foreign Address        (state)
6649A5A4  *.1720                  *.*                    LISTEN
66CDC764  *.1723                  *.*                    LISTEN

Control Plane Policing

For devices which do not need to run SIP, you can use Control Plane Policing (CoPP) to block all SIP access to the device. Cisco IOS software releases 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T support the CoPP feature. CoPP may be configured on a device to protect the management and control planes to minimize the risk and effectiveness of direct infrastructure attacks by explicitly permitting only authorized traffic sent to infrastructure devices in accordance with existing security policies and configurations. The following example can be adapted to your network.

Warning: Because SIP utilizes UDP as a transport, it is possible to spoof the sender's IP address, which may defeat ACLs that permit communication to these ports from trusted IP addresses.

!-- Permit all TCP and UDP SIP traffic sent to all IP addresses
!-- configured on all interfaces of the affected device so that it
!-- will be policed and dropped by the CoPP feature.


access-list 100 permit tcp any any eq 5060
access-list 100 permit udp any any eq 5060


!-- Permit (Police or Drop)/Deny (Allow) all other Layer3 and Layer4
!-- traffic in accordance with existing security policies and
!-- configurations for traffic that is authorized to be sent
!-- to infrastructure devices.



!-- Create a Class-Map for traffic to be policed by
!-- the CoPP feature.


class-map match-all drop-sip-class
  match access-group 100


!-- Create a Policy-Map that will be applied to the
!-- Control-Plane of the device.


policy-map drop-sip-traffic
  class drop-sip-class
    drop


!-- Apply the Policy-Map to the Control-Plane of the
!-- device.


control-plane
  service-policy input drop-sip-traffic

In the above CoPP example, the access control list entries (ACEs) which match the potential exploit packets with the "permit" action result in these packets being discarded by the policy-map "drop" function, while packets that match the "deny" action (not shown) are not affected by the policy-map drop function. Additional information on the configuration and use of the CoPP feature can be found at http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6642/prod_white_paper0900aecd804fa16a.html and http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtrtlimt.html.

Cisco will make free software available to address this vulnerability for affected customers. This advisory will be updated as fixed software becomes available. 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 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 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 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)
  
• +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/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

This issue was first reported to Cisco by a customer. There are no known instances of intentional exploitation of this issue. However, Cisco has observed data streams that appear to be unintentionally triggering the vulnerability.

This advisory is posted on Cisco's worldwide website at:

http://www.cisco.com/warp/public/707/cisco-sa-20070131-sip.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.

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.