Cisco Security Advisory
Cisco IOS Software NAT64 Denial of Service Vulnerability
A vulnerability in the Network Address Translation 64 (NAT64) functions of Cisco IOS Software could allow an unauthenticated, remote attacker to cause either an interface queue wedge or a device reload.
The vulnerability is due to the incorrect handling of certain IPv4 packet streams that are sent through the device. An attacker could exploit this vulnerability by sending specific IPv4 packet streams through the device. An exploit could allow the attacker to either cause an interface queue wedge or a device 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:
This advisory is part of the March 27, 2019, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 17 Cisco Security Advisories that describe 19 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: March 2019 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.
This vulnerability affects devices that are running a vulnerable release of Cisco IOS Software and are configured with either NAT64 (Stateless or Stateful), Mapping of Address and Port Using Translation (MAP-T), or Mapping of Address and Port Using Encapsulation (MAP-E).
For more information about which Cisco IOS Software releases are vulnerable, see the Fixed Software section of this advisory.Determining the NAT64 Configuration
Administrators can identify devices that have either NAT64 (Stateless or Stateful), MAP-T, or MAP-E by using the show running-config | include nat64 enable|nat64 map-t|nat64 map-e command in the CLI. If the command returns output with nat64 in it, the device is vulnerable. The following example shows the output of the command on a device with NAT64 enabled:
Router#show running-config | include nat64 enable|nat64 map-t|nat64 map-e nat64 enable nat64 enable nat64 prefix stateless 2001:DB9:0:1::/96 nat64 route 188.8.131.52/24 GigabitEthernet0/1 Router#
Determining the Cisco IOS Software Release
To determine which Cisco IOS Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS Software, the system banner displays text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The banner also displays the installed image name in parentheses, followed by the Cisco IOS Software release number and release name. Some Cisco devices do not support the show version command or may provide different output.
The following example shows the output of the command for a device that is running Cisco IOS Software Release 15.5(2)T1 and has an installed image name of C2951-UNIVERSALK9-M:
Router> show version Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2015 by Cisco Systems, Inc. Compiled Mon 22-Jun-15 09:32 by prod_rel_team . . .
For information about the naming and numbering conventions for Cisco IOS Software releases, see the Cisco IOS and NX-OS Software Reference Guide.
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 XE Software, Cisco IOS XR Software, or Cisco NX-OS Software.
Queue wedges occur when certain packets are received and queued by a Cisco IOS or IOS XE router or switch but, due to a processing error, are never removed from the queue.
Consult the Workarounds section of this advisory for more information about queue wedges and some detection mechanisms that may be used to identify a blocked interface in Cisco IOS Software. See also the Cisco Security Blog Cisco IOS Queue Wedges Explained.
In the event of exploitation, if the source of the exploit traffic is identified and subsequently blocked so that this traffic doesn't continue to reach the vulnerable device, administrators can increase the hold queue via the interface CLI configuration command hold-queue
inuntil they can reload the router, as shown in the following example:
Router#conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#inte gigabitEthernet 1 Router(config-if)#hold Router(config-if)#hold-queue 350 in Router(config-if)#end Router#
If the device is exploited and results in a queue wedge, the output of the show interface command will show an interface with the size of the input queue being greater than the max, as shown in the following example:
Router#show interface | include Input queue: Input queue: 76/75/180/0 (size/max/drops/flushes); Total output drops: 0
There are no workarounds that address this vulnerability.
The following identification mechanisms exist for the queue wedge exploit for this vulnerability:
Embedded Event Manager
A Cisco IOS Embedded Event Manager (EEM) policy that is based on Tool Command Language (Tcl) can be used on vulnerable Cisco IOS devices to identify and detect an interface queue wedge that is caused by this vulnerability. The policy allows administrators to monitor the interfaces for Cisco IOS device and detect when the interface input queues are full. When Cisco IOS EEM detects potential exploitation of this vulnerability, the policy can trigger a response by sending an alert to the network administrator, who could then decide to implement an upgrade, implement suitable mitigations, or reload the device to clear the input queue.
The Tcl script is available for download from the Cisco Beyond: Embedded Event Manager (EEM) Scripting Community at the following link: https://supportforums.cisco.com/docs/DOC-19337
For additional information, see the Cisco Security Blog Cisco IOS Queue Wedges Explained.
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:
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:
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 Software
To help customers determine their exposure to vulnerabilities in Cisco IOS Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific Cisco IOS 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 Software release-for example, 15.1(4)M2-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.
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 found during internal security testing.
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.
Version Description Section Status Date 1.0 Initial public release. - Final 2019-March-27
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