Cisco Security Advisory
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CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the Network Address Translation (NAT) Session Initiation Protocol (SIP) Application Layer Gateway (ALG) of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload.
The vulnerability is due to improper processing of transient SIP packets on which NAT is performed on an affected device. An attacker could exploit this vulnerability by using UDP port 5060 to send crafted SIP packets through an affected device that is performing NAT for SIP packets. A successful exploit could allow an attacker to cause the device to reload, resulting in a denial of service (DoS) condition.
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-algThis 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.
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Vulnerable Products
This vulnerability affects the following Cisco devices if they are running a vulnerable release of Cisco IOS XE Software that is configured for NAT operation:
- Cisco 1100, 4200, and 4300 Integrated Services Routers (ISRs)
- Cisco Cloud Services Router (CSR) 1000V Series
- Cisco Enterprise Network Compute System (ENCS)
- Cisco Integrated Services Virtual Router (ISRv)
Note: The SIP ALG feature is enabled as soon as NAT is configured on the device.
For information about which Cisco IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.
Assessing the NAT Configuration
To determine whether NAT has been enabled in the Cisco IOS XE Software configuration, the ip nat inside or ip nat outside commands must be on different interfaces and at least one ip nat global configuration command must be in the configuration. Alternatively, in the case of the NAT Virtual Interface, the ip nat enable interface command will be present.
The show running-config | include ip nat command can be used to determine whether NAT is in the configuration, as illustrated in the following example of a vulnerable configuration:
Router#show running-config | include ip nat
ip nat inside
ip nat outside
ip nat inside source static 192.0.2.100 10.0.0.1To determine whether the SIP ALG is disabled in the NAT configuration, use the show running-config | include ip nat privileged EXEC command. The presence of no ip nat service sip in the output of show running-config | include ip nat indicates that the SIP ALG is disabled in the NAT configuration.
The following is the output of show running-config | include ip nat in Cisco IOS XE Software that has the SIP ALG disabled in the NAT configuration:
Router#show running-config | include ip nat
ip nat inside
ip nat outside
ip nat inside source static 192.0.2.100 10.0.0.1 vrf sip
no ip nat service sip udp port 5060If no ip nat service sip does not appear in the output of show running-config | include ip nat, and the device runs an affected version of Cisco IOS XE Software with NAT enabled, that configuration is 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 Software, Cisco IOS XR Software, or Cisco NX-OS Software.
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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.
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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.htmlAdditionally, 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.htmlCustomers 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.
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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.
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This vulnerability was found during internal security testing.
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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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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2019-September-25
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