Summary

• A vulnerability exists in the Session Initiation Protocol (SIP) implementation in Cisco IOS^® Software that could allow an unauthenticated attacker to cause a denial of service (DoS) condition on an affected device when the Cisco Unified Border Element feature is enabled.

  Cisco has released software updates that address this vulnerability. For devices that must run SIP there are no workarounds; however, mitigations are available to limit exposure of the vulnerability.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-sip.

  Note: The September 23, 2009, Cisco IOS Security Advisory bundled publication includes eleven Security Advisories. Ten of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses a vulnerability in Cisco Unified Communications Manager. Each advisory lists the releases that correct the vulnerability or vulnerabilities detailed in the advisory.

  Individual publication links are in "Cisco Event Response: Semiannual Cisco IOS Software Advisory Bundled Publication" at the following link:

  http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_ sep09.html

Affected Products

• This vulnerability only affects devices running Cisco IOS Software with SIP voice services enabled.

  Vulnerable Products

  Cisco devices running affected Cisco IOS Software versions that are configured to process SIP messages with the Cisco Unified Border Element feature are affected. Cisco IOS devices that are not configured for SIP and Cisco Unified Border Element feature are not affected by this vulnerability.

  Note: Cisco Unified Border Element feature (previously known as the Cisco Multiservice IP-to-IP Gateway) is a special Cisco IOS Software image that runs on Cisco multiservice gateway platforms. It provides a network-to-network interface point for billing, security, call admission control, quality of service, and signaling interworking.

  Cisco Unified Border Element feature requires the voice service voip command and the allow-connections subcommand. An example of an affected configuration is as follows:

   voice service voip
     allow-connections from-type to to-type 
  ...
  !

  Recent versions of Cisco IOS Software do not process SIP messages by default. Creating a dial peer by issuing the command dial-peer voice will start the SIP processes, causing the Cisco IOS device to process SIP messages. In addition, several features within Cisco Unified Communications Manager Express, such as ePhones, once configured will also automatically start the SIP process, which will cause the device to start processing SIP messages. An example of an affected configuration is as follows:

  dial-peer voice  voip
   ...
  !

  In addition to inspecting the Cisco IOS device configuration for a dial-peer command that causes the device to process SIP messages, administrators can also use the command show processes | include SIP to determine whether Cisco IOS Software is running the processes that handle SIP messages. In the following example, the presence of the processes CCSIP_UDP_SOCKET or CCSIP_TCP_SOCKET indicates that the Cisco IOS device is processing SIP messages:

      Router#show processes | include SIP
       149 Mwe 40F48254            4          1    400023108/24000  0 CCSIP_UDP_SOCKET
       150 Mwe 40F48034            4          1    400023388/24000  0 CCSIP_TCP_SOCKET

  Warning: Since there are several ways a device running Cisco IOS Software can start processing SIP messages, it is recommended that the show processes | include SIP command be used to determine whether the device is processing SIP messages instead of relying on the presence of specific configuration commands.

  To determine the Cisco IOS Software release that is running on a Cisco product, administrators can log in to the device and issue the show version command to display the system banner. The system banner confirms that the device is running Cisco IOS Software by displaying text similar to "Cisco Internetwork Operating System Software" or "Cisco IOS Software." The image name displays in parentheses, followed by "Version" and the Cisco IOS Software release name. Other Cisco devices do not have the show version command or may provide different output.

  The following example identifies a Cisco product that is running Cisco IOS Software Release 12.3(26) with an installed image name of C2500-IS-L:

  Router#show version
  Cisco Internetwork Operating System Software
  IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2008 by cisco Systems, Inc.
  Compiled Mon 17-Mar-08 14:39 by dchih
  
  
  !--- output truncated
  
  

  The following example identifies a Cisco product that is running Cisco IOS Software Release 12.4(20)T with an installed image name of C1841-ADVENTERPRISEK9-M:

  Router#show version
  Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2008 by Cisco Systems, Inc.
  Compiled Thu 10-Jul-08 20:25 by prod_rel_team
  
  
  !--- output truncated
  
  

  Additional information about Cisco IOS Software release naming conventions is available in "White Paper: Cisco IOS Reference Guide" at the following link: http://www.cisco.com/warp/public/620/1.html

  Products Confirmed Not Vulnerable

  The SIP Application Layer Gateway (ALG), which is used by the Cisco IOS NAT and firewall features of Cisco IOS Software, is not affected by this vulnerability. Cisco IOS XE Software and Cisco IOS XR Software are not affected by this vulnerability. No other Cisco products are currently known to be affected by this vulnerability.

Details

• SIP is a popular signaling protocol that is used to manage voice and video calls across IP networks such as the Internet. SIP is responsible for handling all aspects of call setup and termination. Voice and video are the most popular types of sessions that SIP handles, but the protocol has the flexibility to accommodate other applications that require call setup and termination. SIP call signaling can use UDP (port 5060), TCP (port 5060), or TLS (TCP port 5061) as the underlying transport protocol.

  The Cisco Unified Border Element (previously known as the Cisco Multiservice IP-to-IP Gateway) is a special Cisco IOS Software image that runs on Cisco multiservice gateway platforms. It provides a network-to-network interface point for billing, security, call admission control, quality of service, and signaling interworking.

  For more information about Cisco Unified Border Element refer to the following link:

  http://www.cisco.com/en/US/products/sw/voicesw/ps5640/index.html

  A DoS vulnerability exists in the SIP implementation in Cisco IOS Software when devices are running a Cisco IOS image that contains the Cisco Unified Border Element feature. This vulnerability is triggered by processing a series of crafted SIP messages.

  This vulnerability is documented in Cisco Bug ID CSCsx25880 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2009-2870.

Workarounds

• If the affected Cisco IOS device requires SIP for VoIP services, SIP cannot be disabled, and therefore, no workarounds are available. Users are advised to apply mitigation techniques to help limit exposure to the vulnerability. Mitigation consists of allowing only legitimate devices to connect to the routers. To increase effectiveness, the mitigation must be coupled with anti-spoofing measures on the network edge. This action is required because SIP can use UDP as the transport protocol.

  Additional mitigations that can be deployed on Cisco devices within the network are available in the companion document "Cisco Applied Mitigation Bulletin: Identifying and Mitigating Exploitation of the Denial of Service Vulnerabilities in Cisco Unified Communications Manager and Cisco IOS Software", which is available at the following location: https://sec.cloudapps.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20090923-voice.

  Disable SIP Listening Ports

  For devices that do not require SIP to be enabled, the simplest and most effective workaround is to disable SIP processing on the device. Some versions of Cisco IOS Software allow administrators to accomplish this with the following commands:

  sip-ua
   no transport udp
   no transport tcp
   no transport tcp tls

  Warning: When applying this workaround to devices that are processing Media Gateway Control Protocol (MGCP) or H.323 calls, the device will not 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.

  The show udp connections, show tcp brief all, and show processes | include SIP commands can be used to confirm that the SIP UDP and TCP ports are closed after applying this workaround.

  Depending on the Cisco IOS Software version in use, the output of "show ip sockets" still showed UDP port 5060 open, but sending something to that port caused the SIP process to emit the following message:

  *Feb  2 11:36:47.691: sip_udp_sock_process_read: SIP UDP Listener is
  DISABLED 

  Control Plane Policing

  For devices that need to offer SIP services it is possible to use Control Plane Policing (CoPP) to block SIP traffic to the device from untrusted sources. Cisco IOS 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 the network

  
  !-- The 192.168.1.0/24 network and the 172.16.1.1 host are trusted.
  !-- Everything else is not trusted. The following access list is used
  !-- to determine what traffic needs to be dropped by a control plane
  !-- policy (the CoPP feature.) If the access list matches (permit)
  !-- then traffic will be dropped and if the access list does not
  !-- match (deny) then traffic will be processed by the router.
  
  
  access-list 100 deny udp 192.168.1.0 0.0.0.255 any eq 5060
  access-list 100 deny tcp 192.168.1.0 0.0.0.255 any eq 5060
  access-list 100 deny tcp 192.168.1.0 0.0.0.255 any eq 5061
  access-list 100 deny udp host 172.16.1.1 any eq 5060
  access-list 100 deny tcp host 172.16.1.1 any eq 5060
  access-list 100 deny tcp host 172.16.1.1 any eq 5061
  access-list 100 permit udp any any eq 5060
  access-list 100 permit tcp any any eq 5060
  access-list 100 permit tcp any any eq 5061
  
  
  !-- 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

  Warning: Because SIP can use UDP as a transport protocol, it is possible to easily spoof the IP address of the sender, which may defeat access control lists that permit communication to these ports from trusted IP addresses.

  In the above CoPP example, the access control entries (ACEs) that 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/web/about/security/intelligence/coppwp_gs.html and http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtrtlimt.html.

Fixed Software

• 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) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. 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. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

  Major Release	Availability of Repaired Releases
  Affected 12.0-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.0 based releases.
  Affected 12.1-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.1 based releases.
  Affected 12.2-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.2 based releases.
  Affected 12.3-Based Releases	First Fixed Release	Recommended Release
  12.3	Not Vulnerable
  12.3B	Not Vulnerable
  12.3BC	Not Vulnerable
  12.3BW	Not Vulnerable
  12.3EU	Not Vulnerable
  12.3JA	Not Vulnerable
  12.3JEA	Not Vulnerable
  12.3JEB	Not Vulnerable
  12.3JEC	Not Vulnerable
  12.3JK	Not Vulnerable
  12.3JL	Not Vulnerable
  12.3JX	Not Vulnerable
  12.3T	Not Vulnerable
  12.3TPC	Not Vulnerable
  12.3VA	Not Vulnerable
  12.3XA	Not Vulnerable
  12.3XB	Not Vulnerable
  12.3XC	Not Vulnerable
  12.3XD	Not Vulnerable
  12.3XE	Not Vulnerable
  12.3XF	Not Vulnerable
  12.3XG	Not Vulnerable
  12.3XI	Not Vulnerable
  12.3XJ	Not Vulnerable
  12.3XK	Not Vulnerable
  12.3XL	Not Vulnerable
  12.3XQ	Not Vulnerable
  12.3XR	Not Vulnerable
  12.3XS	Not Vulnerable
  12.3XU	Not Vulnerable
  12.3XW	Not Vulnerable
  12.3XX	Not Vulnerable
  12.3XY	Not Vulnerable
  12.3XZ	Not Vulnerable
  12.3YA	Not Vulnerable
  12.3YD	Not Vulnerable
  12.3YF	Not Vulnerable
  12.3YG	Not Vulnerable
  12.3YH	Not Vulnerable
  12.3YI	Not Vulnerable
  12.3YJ	Not Vulnerable
  12.3YK	Releases prior to 12.3(11)YK3 are vulnerable, release 12.3(11)YK3 and later are not vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.3YM	Not Vulnerable
  12.3YQ	Not Vulnerable
  12.3YS	Vulnerable; first fixed in 12.4T Releases up to and including 12.3(11)YS1 are not vulnerable.	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.3YT	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.3YU	Not Vulnerable
  12.3YX	Not Vulnerable
  12.3YZ	Not Vulnerable
  12.3ZA	Not Vulnerable
  Affected 12.4-Based Releases	First Fixed Release	Recommended Release
  12.4	Not Vulnerable
  12.4GC	12.4(24)GC1
  12.4JA	Not Vulnerable
  12.4JDA	Not Vulnerable
  12.4JDC	Not Vulnerable
  12.4JDD	Not Vulnerable
  12.4JK	Not Vulnerable
  12.4JL	Not Vulnerable
  12.4JMA	Not Vulnerable
  12.4JMB	Not Vulnerable
  12.4JX	Not Vulnerable
  12.4MD	Not Vulnerable
  12.4MDA	Not Vulnerable
  12.4MR	12.4(19)MR3	12.4(19)MR3
  12.4SW	Not Vulnerable
  12.4T	12.4(24)T1 12.4(15)T10 12.4(20)T3 12.4(22)T2	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XA	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XB	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XC	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XD	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XE	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XF	Not Vulnerable
  12.4XG	Not Vulnerable
  12.4XJ	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XK	Not Vulnerable
  12.4XL	12.4(15)XL5
  12.4XM	Vulnerable; first fixed in 12.4T Releases up to and including 12.4(15)XM are not vulnerable.	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XN	Not Vulnerable
  12.4XP	Vulnerable; Contact your support organization per the instructions in Obtaining Fixed Software section of this advisory
  12.4XQ	Not Vulnerable
  12.4XR	Not Vulnerable
  12.4XT	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XV	Vulnerable; Contact your support organization per the instructions in Obtaining Fixed Software section of this advisory
  12.4XW	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XY	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4XZ	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4YA	Vulnerable; first fixed in 12.4T	12.4(15)T10 12.4(20)T4 12.4(22)T3 12.4(24)T2; Available on 23-OCT-2009
  12.4YB	12.4(22)YB1	12.4(22)YB4
  12.4YD	Not Vulnerable
  12.4YE	Not Vulnerable

  Note: No Cisco IOS-XE or Cisco IOS Software Modularity releases are affected by this vulnerability.

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 discovered during internal testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-sip

Revision History

• Revision 1.0

  2009-September-23

  Initial public release

  Show Less