Summary

• A vulnerability in the common Session Initiation Protocol (SIP) library of Cisco IOS and IOS XE Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to insufficient sanity checks on an internal data structure. An attacker could exploit this vulnerability by sending a sequence of malicious SIP messages to an affected device. An exploit could allow the attacker to cause a NULL pointer dereference, resulting in a crash of the iosd process. This triggers a reload of the device.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190925-sip-dos

  This advisory is part of the September 25, 2019, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 12 Cisco Security Advisories that describe 13 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: September 2019 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco routers that are running a vulnerable release of Cisco IOS or IOS XE Software with any of the following features enabled:

  • Cisco Unified Border Element (CUBE)
  • Cisco Unified Communications Manager Express (CME)
  • Cisco IOS Gateways with Session Initiation Protocol (SIP)
  • Cisco TDM Gateways
  • Cisco Unified Survivable Remote Site Telephony (SRST)
  • Cisco Business Edition 4000 (BE4K)

  For more information about which Cisco IOS and IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine Whether a Device is Vulnerable

  To determine whether a device is vulnerable, administrators can use the show processes | include CCSIP_SPI_CONTRO command in the CLI and look for the presence of the CCSIP_SPI_CONTRO process. The following example shows the output of the show processes | include CCSIP_SPI_CONTRO command on a device that has at least one of the affected features enabled and is thus vulnerable:

  Router#show processes | include CCSIP_SPI_CONTRO
   671 Mwe 561F108FE8BA            10         11     909234584/240000  0 CCSIP_SPI_CONTRO

  Empty output of this command would indicate that none of the affected features are enabled and the device is not vulnerable.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect Cisco IOS XR Software or Cisco NX-OS Software.

Indicators of Compromise

• A successful exploit of this vulnerability will cause an affected device to reload and generate a crashinfo file.

  A successful exploit of this vulnerability may be confirmed by decoding the stack trace for the device and determining whether the stack trace correlates with this vulnerability.

  Contact the Cisco Technical Assistance Center (TAC) to review the crashinfo file and determine whether the device has been compromised by exploitation of this vulnerability.

Workarounds

• There are no workarounds that address this vulnerability.

  Customers who do not use any SIP feature but who have other voice-related features enabled, which automatically enable the SIP processes in Cisco IOS Software and Cisco IOS XE Software releases prior to Release 16.11, can shut down the SIP ports by issuing the following commands in global configuration mode:

  Router(config)#sip-ua
  Router(config-sip-ua)#no transport udp
  Router(config-sip-ua)#no transport tcp
  Router(config-sip-ua)#no transport tcp tls

  Alternatively, customers can block traffic targeted to the designated SIP ports using infrastructure access control lists (iACLs). Using iACLs is a network security best practice and should be considered as a long-term addition to good network security as well as a mitigation for this specific issue. To help protect all devices with IP addresses in the infrastructure IP address range, customers are advised to include the following iACL example as part of the deployed iACL:

  !---
  !--- Feature: SIP
  !---
  
  !---  
  !--- Deny SIP traffic from all other sources destined
  !--- to infrastructure addresses
  !---
  
  access-list 150 deny udp any INFRASTRUCTURE_ADDRESSES WILDCARD eq 5060
  access-list 150 deny tcp any INFRASTRUCTURE_ADDRESSES WILDCARD eq 5060
  access-list 150 deny tcp any INFRASTRUCTURE_ADDRESSES WILDCARD eq 5061
  
  !---
  !--- Permit/deny all other Layer 3 and Layer 4 traffic in
  !--- accordance with existing security policies and
  !--- configurations. Permit all other traffic to transit the
  !--- device.
  !---
  
  access-list 150 permit ip any any
  
  !---
  !--- Apply access-list to all interfaces (only one example
  !--- shown)
  !---
  
  interface GigabitEthernet 2/0
   ip access-group 150 in

  For further guidelines and recommendations for deployment techniques for iACLs, see the white paper Protecting Your Core: Infrastructure Protection Access Control Lists and the Cisco Guide to Harden Cisco IOS Devices.

  Note: By default, SIP uses UDP and TCP port 5060 for SIP and TCP port 5061 for SIP over TLS. However, these ports are user-configurable using the listen-port non-secure <port_number> and listen-port secure <port_number> commands in voices service voip > sip configuration mode. If custom SIP ports have been configured, the UDP and TCP ports in the previous example iACL would need to be adjusted accordingly.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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.

  Customers Without Service Contracts

  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC:
  https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.

  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).

  Customers can use this tool to perform the following tasks:

  • Initiate a search by choosing one or more releases from a drop-down list or uploading a file from a local system for the tool to parse
  • Enter the output of the show version command for the tool to parse
  • Create a custom search by including all previously published Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication

  To determine whether a release is affected by any published Cisco Security Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS or IOS XE Software release—for example, 15.1(4)M2 or 3.13.8S—in the following field:

  By default, the Cisco IOS Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, use the Cisco IOS Software Checker on Cisco.com and check the Medium check box in the Impact Rating drop-down list.

  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.

Exploitation and Public Announcements

• 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.

Source

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190925-sip-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Added mitigation options.	Workarounds	Final	2019-October-04
  1.0	Initial public release.	—	Final	2019-September-25

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