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Cisco Security Advisory

Cisco IOS Software Session Initiation Protocol Denial of Service Vulnerabilities

High
Advisory ID:
cisco-sa-20110928-sip
First Published:
2011 September 28 16:00 GMT
Last Updated:
2012 September 21 19:22 GMT
Version 1.1:
Final
Workarounds:
See below
CVE-2011-0939
CVE-2011-2072
CVE-2011-3275
CVSS Score:
Base 7.8, Temporal 6.4Click Icon to Copy Verbose Score
AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
CVE-2011-0939
CVE-2011-2072
CVE-2011-3275

Summary

  • Multiple vulnerabilities exist in the Session Initiation Protocol (SIP) implementation in Cisco IOS Software and Cisco IOS XE Software that could allow an unauthenticated, remote attacker to cause a reload of an affected device or trigger memory leaks that may result in system instabilities. Affected devices would need to be configured to process SIP messages for these vulnerabilities to be exploitable.

    Cisco has released software updates that address these vulnerabilities. There are no workarounds for devices that must run SIP; however, mitigations are available to limit exposure to the vulnerabilities.

     This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110928-sip.

    Note: The September 28, 2011, Cisco IOS Software Security Advisory bundled publication includes ten Cisco Security Advisories. Nine of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses a vulnerability in Cisco Unified Communications Manager. Each advisory lists the Cisco IOS Software releases that correct the vulnerability or vulnerabilities detailed in the advisory as well as the Cisco IOS Software releases that correct all vulnerabilities in the September 2011 Bundled Publication.

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

    http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep11.html

    Cisco Unified Communications Manager is affected by one of the vulnerabilities described in this advisory. A separate Cisco Security Advisory has been published to disclose the vulnerability that affects the Cisco Unified Communications Manager at the following location:

    https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110928-cucm

Affected Products

  • Vulnerable Products

    Cisco devices are affected when they are running affected Cisco IOS Software and Cisco IOS XE Software versions that are configured to process SIP messages.

    Recent versions of Cisco IOS Software do not process SIP messages by default. Creating a dial peer by issuing the dial-peer voice configuration command 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, will also automatically start the SIP process when they are configured, causing the device to start processing SIP messages. An example of an affected configuration 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 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:

    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

    Note: Because 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.

    Cisco Unified Border Element images are also affected by two of these vulnerabilities.

    Note: The Cisco Unified Border Element feature (CUBE; 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.

    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

!--- output truncated

    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.

    Cisco IOS XE Software is affected by these vulnerabilities.

    Note: Cisco Unified Communications Manager is affected by one of the vulnerabilities described in this advisory. A separate Cisco Security Advisory has been published to disclose the vulnerability that affects the Cisco Unified Communications Manager at the following location:

    https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110928-cucm

    Products Confirmed Not Vulnerable

    The SIP Application Layer Gateway (ALG), which is used by the Cisco IOS Network Address Translation (NAT) and firewall features of Cisco IOS Software, is not affected by these vulnerabilities.

    Cisco IOS XR Software is not affected by these vulnerabilities.

    No other Cisco products are currently known to be affected by these vulnerabilities.

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 Transport Layer Security (TLS; TCP port 5061) as the underlying transport protocol.

    Multiple vulnerabilities exist in the SIP implementation in Cisco IOS Software that could allow a remote attacker to cause an affected device to reload or to trigger memory leaks that may result in system instabilities. These vulnerabilities are triggered when the device that is running Cisco IOS Software processes crafted SIP messages. Only traffic destined to the device can trigger the vulnerabilities; transit SIP traffic is not an exploit vector.

    Note: In cases where SIP is running over TCP transport, a TCP three-way handshake is necessary to exploit these vulnerabilities.

    The vulnerabilities are as follow:

    CSCth03022 (registered customers only) may cause a reload of an affected device. This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2011-0939.

    CSCti48504 (registered customers only) may cause memory leaks. This vulnerability has been assigned CVE ID CVE-2011-3275.

    CSCto88686 (registered customers only) may cause memory leaks or reloads of affected devices. This vulnerability has been assigned CVE ID CVE-2011-2072.

    Note: this vulnerability also affects Cisco Unified Communications Manager. The corresponding Cisco bug ID is CSCtl86047 (registered customers only) . Refer to the separate Cisco Security Advisory for the Cisco Unified Communications Manager for additional details.

Workarounds

  • 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 vulnerabilities. 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 "Cisco Applied Mitigation Bulletin:Identifying and Mitigating Exploitation of the Multiple Vulnerabilities in Cisco Voice Products", which is available at the following location: https://sec.cloudapps.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20110928-voice.

    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 versions 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

    warningWarning: 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, 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:

    *Jun 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

    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.

    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

Exploitation and Public Announcements

  • The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory.

    These vulnerabilities were discovered by Cisco during internal testing.

Cisco Security Vulnerability Policy

  • 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 History

  • Revision 1.1

    2011-September-30

    Update IOS Software table bundled publication first fixed information.

    Revision 1.0

    2011-September-28

    Initial public release.

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Cisco Security Vulnerability Policy

  • 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.

Subscribe to Cisco Security Notifications

Action Links for This Advisory

Related to This Advisory