A vulnerability in the SM-1T3/E3 firmware on Cisco Second Generation Integrated Services Routers (ISR G2) and the Cisco 4451-X Integrated Services Router (ISR4451-X) could allow an unauthenticated, remote attacker to cause the ISR G2 Router or the SM-1T3/E3 module on the ISR4451-X to reload, resulting in a denial of service (DoS) condition on an affected device.
The vulnerability is due to improper handling of user input. An attacker could exploit this vulnerability by first connecting to the SM-1T3/E3 module console and entering a string sequence. A successful exploit could allow the attacker to cause the ISR G2 Router or the SM-1T3/E3 module on the ISR4451-X to reload, resulting in a DoS condition on an affected device.
Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.
This advisory is available at the following link:This advisory is part of the September 26, 2018, 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 2018 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.
The Cisco SM-X-1T3/E3 1-port T3/E3 enhanced service module (SM-X) is a software-configurable T3/E3 product supported on the Cisco ISR G2 and Cisco ISR4451-X Routers.
This vulnerability affects Cisco ISR G2 or Cisco ISR4451-X Routers if they have an SM-X-1T3/E3 module installed and are running an affected version of Cisco IOS or IOS XE Software.
For information about which Cisco IOS and IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.
Determining if an SM-X-1T3/E3 Module is Installed
On Cisco ISR G2 Routers, enter the show version CLI command. If the output contains Subrate T3/E3 port, then the device has an affected module installed. The following example shows a device with an SM-X-1T3/E3 module installed:
ISR-G2#show version | include T3/E3 1 Subrate T3/E3 port ISR-G2#
If the output returns nothing, then the device does not have an SM-X-1T3/E3 module installed.
On ISR4451-X Routers, enter the show diag all eeprom | include SM-X-1T3 CLI command. If the output contains SM-X-1T3/E3, then the device has an affected module installed. The following example shows a device with an SM-X-1T3/E3 module installed:
ISR-G2#sho diag all eeprom | include SM-X-1T3 Product Identifier (PID) : SM-X-1T3/E3 ISR-G2#
If the output returns nothing, then the device does not have an SM-X-1T3/E3 module installed.
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.
Determining the Cisco IOS XE Software Release
To determine which Cisco IOS XE 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 XE Software, the system banner displays Cisco IOS Software, Cisco IOS XE Software, or similar text.
The following example shows the output of the command for a device that is running Cisco IOS XE Software Release 16.2.1 and has an installed image name of CAT3K_CAA-UNIVERSALK9-M:
ios-xe-device# show version Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2016 by Cisco Systems, Inc. Compiled Sun 27-Mar-16 21:47 by mcpre . . .
For information about the naming and numbering conventions for Cisco IOS XE 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 NX-OS Software or Cisco IOS XR Software.
The firmware for the SM-X-1T3/E3 module is bundled within the Cisco IOS or IOS XE Software image.
This vulnerability is exploitable only when a user has a session to the SM-X-1T3/E3 console.
On ISR G2 Routers prior to Cisco Bug ID CSCuz92665, the SM-X-1T3/E3 console was remotely accessible based on the configuration of the TTY line. See the Workarounds section to change the configuration to prevent remote access to the SM-X-1T3/E3 console. If you are using local authentication on the ISR G2 Router, the line may be accessible without authentication. If you are using authentication, authorization, and accounting (AAA) for authentication, then a valid username and password combination are required to remotely access the module.
On ISR4451-X Routers, the SM-X-1T3/E3 console is only available locally by using the privilege 15 hw-module session <slot/card> command.
Impact of Exploit
On ISR G2 Routers, the entire router will reload when the vulnerability is exploited.
On ISR4451-X Routers, only the SM-X-1T3/E3 module will reload.
On both devices, the SM-X-1T3/E3 module will be down for at least 180 seconds.
Upgrading to a Fixed Software Release - ISR G2 Routers Only
Prior to upgrading to a fixed software release on ISR G2 Routers, delete the existing firmware on the device. The following CLI output shows an example of the applicable commands:
ISR-G2#delete flash0:/firmware/sm_1t3e3/sm_1t3e3_fw.ver Delete filename [/firmware/sm_1t3e3/sm_1t3e3_fw.ver]? Delete flash0:/firmware/sm_1t3e3/sm_1t3e3_fw.ver? [confirm] ISR-G2# ISR-G2#delete flash0:/firmware/sm_1t3e3/sm_1t3e3_fw.img Delete filename [/firmware/sm_1t3e3/sm_1t3e3_fw.img]? Delete flash0:/firmware/sm_1t3e3/sm_1t3e3_fw.img? [confirm] ISR-G2#
While the following workaround does not prevent exploitation of the vulnerability, it does limit the attack surface:
Prevent Access to the SM-X-1T3/E3 Console (ISR G2 Routers Only)
It is recommended that access to the SM-X-1T3/E3 console be disabled by configuring transport input none on the associated line for the SM-X-1T3/E3 console as in the following example:
ISR-G2#configure terminal ISR-G2(config)#line 68 ISR-G2(config)#transport input none ISR-G2(config)#exit ISR-G2#
On Cisco ISR4451-X Routers, the SM-X-1T3/E3 console is only available locally by using the privilege 15 hw-module session <slot/card> command
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 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 Software or Cisco 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.
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 2018-September-26
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