Cisco IOS XR Software Intermediate System-to-Intermediate System Denial of Service Vulnerability

Summary

• A vulnerability in the implementation of the Intermediate System-to-Intermediate System (IS-IS) routing protocol functionality in Cisco IOS XR Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition in the IS-IS process.

  The vulnerability is due to improper handling of a Simple Network Management Protocol (SNMP) request for specific Object Identifiers (OIDs) by the IS-IS process. An attacker could exploit this vulnerability by sending a crafted SNMP request to the affected device. A successful exploit could allow the attacker to cause a DoS condition in the IS-IS process.

  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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200122-ios-xr-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices if they are running Cisco IOS XR Software releases earlier than 6.6.3, 7.0.2, 7.1.1, or 7.2.1 and they configured with both the IS-IS routing protocol and SNMP versions 1, 2c, or 3.

  Cisco has confirmed that this vulnerability affects both Cisco IOS XR 32-bit Software and Cisco IOS XR 64-bit Software.

  Determine Whether the Device Has a Vulnerable Configuration

  To determine if the device is configured for IS-IS routing, administrators can use the show running-config router isis EXEC command in the CLI. If the device is configured for IS-IS routing, this command will return output. The following example shows the partial output of the show running-config router isis command on a device that is configured for IS-IS routing.

  #show running-config router isis
  router isis {isp}
  is-type level-2-only
  ...

  To determine if the device is configured for SNMP, administrators can use the show running-config snmp EXEC command in the CLI. If the device is configured for SNMP, this command will return output. The following examples show the partial output of the show running-config snmp command on a device that is configured for SNMP. Only one version of SNMP needs to be configured for the device to be vulnerable. The vulnerability is triggered through an SNMP query, but the configuration can be for read or write.

  SNMPv1

  #show running-config snmp
  snmp-server community {public ro}
  ...

  SNMPv2

  #show running-config snmp
  snmp-server group {SNMP_GROUP1} v2c
  ...

  SNMPv3

  #show running-config snmp
  snmp-server view {SNMP_VIEW1 1.3.6.1.2.1.1.5 included}
  snmp-server group {SNMP_GROUP1} v3 {auth read SNMP_VIEW1}
  ...

  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 the following Cisco products:

  • Cisco IOS and IOS XE Software
  • Cisco IOS XR7-LNT Software
  • Cisco NX-OS Software

Workarounds

• There are no workarounds that address this vulnerability. However, administrators may choose to perform one of the following mitigations:

  Disable SNMP: This vulnerability is exploited by doing an SNMP query of a special MIB OID range. If SNMP is disabled, this vulnerability cannot be exploited. For mitigation of this vulnerability if SNMP is enabled on the device, contact Cisco TAC for assistance with the OIDs.

  Configure an access control list: Administrators can also configure an access control list (ACL) on an SNMP community to filter incoming SNMP requests to ensure that SNMP queries are performed only by trusted SNMP clients. For information about configuring ACLs, see the Cisco Guide to Harden Cisco IOS XR Devices.

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.

  Fixed Releases

  Cisco fixed this vulnerability in Cisco IOS XR Software Release 6.6.3. Cisco also plans to fix this vulnerability in Cisco IOS XR Software releases 7.0.2, 7.1.1, and 7.2.1.

  Customers are advised to install the appropriate SMU as shown in the following table. Customers who require SMUs for other platforms and releases are advised to contact their support organization.

  IOS XR Release	Platform	SMU Name
  4.3.2	XR12000	c12k-4.3.2.CSCvr62342
  5.2.5	NCS6K	ncs6k-5.2.5.CSCvr62342
  6.1.2	ASR9K-PX	asr9k-px-6.1.2.CSCvr62342
  6.1.3	ASR9K-PX	asr9k-px-6.1.3.CSCvr62342
  6.1.3	NCS5K	ncs5k-6.1.3.CSCvr62342
  6.1.3	NCS5500	ncs5500-6.1.3.CSCvr62342
  6.1.4	ASR9K-PX	asr9k-px-6.1.4.CSCvr6234
  6.1.4	CRS-PX	hfr-px-6.1.4.CSCvr62342
  6.1.4	NCS5500	ncs5500-6.1.4.CSCvr62342
  6.1.4	NCS5K	ncs5k-6.1.4.CSCvr62342
  6.1.4	XRV9K	xrv9k-6.1.4.CSCvr62342
  6.2.2	ASR9K-PX	asr9k-px-6.2.2.CSCvr62342
  6.2.2	NCS6K	ncs6k-6.2.2.CSCvr62342
  6.2.25	NCS5K	ncs5k-6.2.25.CSCvr62342
  6.2.25	NCS6K	ncs6k-6.2.25.CSCvr62342
  6.2.3	NCS5K	ncs5k-6.2.3.CSCvr62342
  6.2.3	ASR9K-PX	asr9k-px-6.2.3.CSCvr62342
  6.2.3	ASR9K-X64	asr9k-x64-6.2.3.CSCvr62342
  6.2.3	CRS-PX	hfr-px-6.2.3.CSCvr62342
  6.2.3	NCS5500	ncs5500-6.2.3.CSCvr62342
  6.2.3	XRV9K	xrv9k-6.2.3.CSCvr62342
  6.2.3	NCS6K	ncs6k-6.2.3.CSCvr62342
  6.3.15	NCS5500	ncs5500-6.3.15.CSCvr62342
  6.3.2	ASR9K-PX	asr9k-px-6.3.2.CSCvr62342
  6.3.2	ASR9K-X64	asr9k-x64-6.3.2.CSCvr62342
  6.3.3	ASR9K-X64	asr9k-x64-6.3.3.CSCvr62342
  6.3.3	ASR9K-PX	asr9k-px-6.3.3.CSCvr62342
  6.3.3	NCS5K	ncs5k-6.3.3.CSCvr62342
  6.3.3	NCS540	ncs540-6.3.3.CSCvr62342
  6.3.3	NCS5500	ncs5500-6.3.3.CSCvr62342
  6.3.3	NCS6K	ncs6k-6.3.3.CSCvr62342
  6.4.2	ASR9K-PX	asr9k-px-6.4.2.CSCvr62342
  6.4.2	ASR9K-X64	asr9k-x64-6.4.2.CSCvr62342
  6.4.2	CRS-PX	hfr-px-6.4.2.CSCvr62342
  6.4.2	NCS5K	ncs5k-6.4.2.CSCvr62342
  6.4.2	NCS6K	ncs6k-6.4.2.CSCvr62342
  6.4.2	XRV9K	xrv9k-6.4.2.CSCvr62342
  6.5.2	ASR9K-PX	asr9k-px-6.5.2.CSCvr62342
  6.5.2	ASR9K-X64	asr9k-x64-6.5.2.CSCvr62342
  6.5.2	NCS5K	ncs5k-6.5.2.CSCvr62342
  6.5.2	NCS5500	ncs5500-6.5.2.CSCvr62342
  6.5.3	ASR9K-X64	asr9k-x64-6.5.3.CSCvr62342
  6.5.3	NCS5500	ncs5500-6.5.3.CSCvr62342
  6.5.3	NCS540	ncs540-6.5.3.CSCvr62342
  6.5.3	NCS5K	ncs5k-6.5.3.CSCvr62342
  6.5.3	ASR9K-PX	asr9k-px-6.5.3.CSCvr62342
  6.5.3	XRV9K	xrv9k-6.5.3.CSCvr62342
  6.6.1	NCS5500	ncs5500-6.6.1.CSCvr62342
  6.6.2	ASR9K-PX	asr9k-px-6.6.2.CSCvr62342
  6.6.2	ASR9K-X64	asr9k-x64-6.6.2.CSCvr62342
  6.6.2	XRV9K	xrv9k-6.6.2.CSCvr62342
  6.6.25	NCS5500	ncs5500-6.6.25.CSCvr62342
  6.6.25	NCS540	ncs540-6.6.25.CSCvr62342
  6.6.25	NCS560	ncs560-6.6.25.CSCvr62342

  To download the SMUs from the Software Center on Cisco.com, do the following:

  1. Click Browse All.
  2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical Networking or Routers.
  3. Choose a specific product and model from the right pane of the product selector.
  4. Choose a release from the left pane of the product page.

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200122-ios-xr-dos

Revision History

• Version	Description	Section	Status	Date
  1.2	Updated Fixed Releases table to add current SMUs.	Fixed Releases	Final	2020-February-19
  1.1	Changed en dashes to hyphens throughout. No content changes were made.	Title, Summary, and Vulnerable Products.	Final	2020-February-04
  1.0	Initial public release.	-	Final	2020-January-22

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