AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
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A vulnerability exists in the Session Initiation Protocol (SIP) implementation in Cisco IOS Software that could allow an unauthenticated, remote attacker to cause a reload of an affected device or cause memory leaks that may result in system instabilities. To exploit this vulnerability, affected devices must be configured to process SIP messages. Limited Cisco IOS Software releases are affected.
Cisco has released 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:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20131106-sip
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Vulnerable Products
Cisco devices are affected when they are running affected Cisco IOS Software releases that are configured to process SIP messages. The following Cisco IOS Software releases are affected by this vulnerability:- 15.1(4)GC and 15.1(4)GC1
- 15.1(4)M4, 15.1(4)M5 and 15.1(4)M6
!
dial-peer voice <Voice dial-peer tag> voip
...
!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: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
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Cisco IOS XE Software and Cisco Unified Communications Manager are not affected by this vulnerability. No other Cisco products are currently known to be affected by this vulnerability.
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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 Transport Layer Security (TLS) on TCP port 5061 as the underlying transport protocol.
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.
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If the affected Cisco IOS device requires SIP for VoIP services, SIP cannot be disabled, and 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 affected devices. 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 "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 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 releases of Cisco IOS Software allow administrators to disable SIP with the following commands:sip-ua
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 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 specific network configurations:!– 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.
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When considering software upgrades, customers are advised to consult the Cisco Security Advisories, Responses, and Notices archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.
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 Software
Each 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 (SIO) portal at http://tools.cisco.com/security/center/selectIOSVersion.x
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
This vulnerability was discovered by Cisco during the handling of customer service requests.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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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.
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