Advisory ID: cisco-sa-20131106-sip
Last Updated 2013 November 15 16:42 UTC (GMT)
For Public Release 2013 November 6 16:00 UTC (GMT)
Vulnerability Scoring Details
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: Final
Cisco Security Procedures
Cisco has released free software updates that address this vulnerability.
There are no workarounds for devices that must run SIP; however, mitigations are available to limit exposure to the vulnerability.
This advisory is available at the following link:
- 15.1(4)GC and 15.1(4)GC1
- 15.1(4)M4, 15.1(4)M5 and 15.1(4)M6
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 show processes | include SIP command 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 will process SIP messages:
dial-peer voice <Voice dial-peer tag> voip
Note: Because there are several ways that 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.
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
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 15.0(1)M1 with an installed image name of C3900-UNIVERSALK9-M:
Additional information about Cisco IOS Software release naming conventions is available in the white paper Cisco IOS and NX-OS Software Reference Guide available at: http://www.cisco.com/web/about/security/intelligence/ios-ref.html.
Router> show version Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2009 by Cisco Systems, Inc. Compiled Wed 02-Dec-09 17:17 by prod_rel_team
!–- output truncated
A vulnerability in session initiation protocol functionality of Cisco IOS Software could allow an unauthenticated, remote attacker to trigger a memory leak or a device reload.
The vulnerability is due to incorrect processing of specially crafted SIP messages. An attacker could exploit this vulnerability by sending specific valid SIP messages to the SIP gateway. An exploit could allow the attacker to trigger a memory leak or a device reload.
This vulnerability is triggered when a device that is running Cisco IOS Software processes specific, valid SIP messages. Only traffic destined to the device can trigger the vulnerability; transit SIP traffic is not an exploit vector. This vulnerability can be exploited with SIP over IPv4 or IPv6 communications protocol.
Note: In cases where SIP is running over TCP transport, a TCP three-way handshake is necessary to exploit this vulnerability.
This vulnerability is documented in Cisco bug ID: CSCuc42558 (registered customers only) and CSCug25383 (registered customers only). This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2013-5553.
CVSS is a standards-based scoring method that conveys vulnerability severity and helps organizations determine the urgency and priority of a response.
Cisco has provided a base and temporal score. Customers can also compute environmental scores that help determine the impact of the vulnerability in their own networks.
Cisco has provided additional information regarding CVSS at the following link:
Cisco has also provided a CVSS calculator to compute the environmental impact for individual networks at the following link:
CSCuc42558 and CSCug25383 - Cisco IOS Software Session Initiation Protocol Denial of Service Vulnerability
Calculate the environmental score of CSCuc42558 and CSCug25383
CVSS Base Score - 7.8
CVSS Temporal Score - 6.4
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
Cisco IOS SoftwareEach row of the following Cisco IOS Software table corresponds to a Cisco IOS Software train. If a particular train is vulnerable, the earliest releases that contain the fix are listed in the First Fixed Release column. Cisco recommends upgrading to the latest available release, where possible.
The Cisco IOS Software Checker allows customers to search for Cisco Security Advisories that address specific Cisco IOS Software releases. This tool is available on the Cisco Security Intelligence Operations (SIO) portal at http://tools.cisco.com/security/center/selectIOSVersion.x
Additional mitigations that can be deployed on Cisco devices within the network are available in the companion document "Identifying and Mitigating Exploitation of the Cisco IOS Software Session Initiation Protocol Denial of Service Vulnerability", which is available at the following link: http://tools.cisco.com/security/center/viewAMBAlert.x?alertId=31516
Disabling SIP Listening PortsFor devices that do not require SIP to be enabled, the simplest and most effective workaround is to disable SIP processing on the device. Some releases of Cisco IOS Software allow administrators to disable SIP with the following commands:
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.
no transport udp
no transport tcp
no transport tcp tls
The show udp connections, show tcp brief all, and show control-plane host open-ports 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 release in use, when SIP is disabled the output from the show ip sockets command may still show the SIP ports open, but sending traffic to them will cause the SIP process to emit the following message:
*Nov 2 11:36:47.691: sip_udp_sock_process_read: SIP UDP Listener is DISABLED
Control Plane PolicingFor 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 specific network configurations:
Note: Because SIP can use UDP as a transport protocol, it is possible to spoof the source address of an IP packet, which may bypass access control lists that permit communication to these ports from trusted IP addresses. Additional information on understanding unicast reverse path forwarding can be found at http://www.cisco.com/web/about/security/intelligence/unicast-rpf.html
!– 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 control-plane-policy class drop-sip-class drop
!– Apply the Policy-Map to the Control-Plane of the !– device. control-plane service-policy input control-plane-policy
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.
Customers may only install and expect support for feature sets they have purchased. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html.
The effectiveness of any workaround or fix depends on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Because of the variety of affected products and releases, customers should consult their service providers or support organizations to ensure that any applied workaround or fix is the most appropriate in the intended network before it is deployed.
- +1 800 553 2447 (toll free from within North America)
- +1 408 526 7209 (toll call from anywhere in the world)
- email: email@example.com
Refer to Cisco Worldwide Contacts at http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, instructions, and email addresses for support in various languages.
This vulnerability was discovered by Cisco during the handling of customer service requests.
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|Revision 1.1||2013-November-15||Minor changes to wording of "Disabling SIP Listening Ports" section in Workarounds.|
|Revision 1.0||2013-November-06||Initial public release.|