Summary

• Multiple vulnerabilities in Cisco Network Convergence System (NCS) 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for the Cisco 8000 Series Routers could allow an authenticated, local attacker to execute unsigned code during the boot process on an affected device.

  For more information about these vulnerabilities, see the Details section of this advisory.

  Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ioxr-l-zNhcGCBt

Affected Products

• Vulnerable Products

  These vulnerabilities affect the following Cisco devices if they are running a vulnerable release of Cisco IOS XR Software:

  • 8000 Series Routers
  • NCS 540 Series Routers that are running the NCS540L images

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine the Software Version

  To determine whether the device is running an NCS540L software image, log in to the device and issue the show version command. If the output indicates LNT, as shown in the following example, then the device is affected by these vulnerabilities.

  Router#show version
  Cisco IOS XR Software, Version 7.0.1 LNT
  Copyright (c) 2013-2019 by Cisco Systems, Inc.Build Information:

  Products Confirmed Not Vulnerable

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

Details

• The vulnerabilities are not dependent on one another. Exploitation of one of the vulnerabilities is not required to exploit the other vulnerability. In addition, a software release that is affected by one of the vulnerabilities may not be affected by the other vulnerability.

  Details about the vulnerabilities are as follows:

  CVE-2021-1136: Cisco IOS XR Software for Cisco 8000 Series Routers and Network Convergence System 540 Series Routers GRUB Boot Loader Vulnerability

  A vulnerability in the GRUB boot loader of Cisco NCS 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for the Cisco 8000 Series Routers could allow an authenticated, local attacker to execute unsigned code during the boot process on an affected device.

  The vulnerability is due to an unlocked version of GRUB boot loader on an affected device. An attacker could exploit this vulnerability by modifying the boot process from the GRUB menu. A successful exploit could allow the attacker to bypass the boot chain of trust.

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

  Bug ID(s): CSCvs70887
  CVE ID: CVE-2021-1136
  Security Impact Rating (SIR): High
  CVSS Base Score: 6.7
  CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

  CVE-2021-1244: Cisco IOS XR Software for Cisco 8000 Series Routers and Network Convergence System 540 Series Routers Unsigned Boot File Vulnerability

  A vulnerability in the signing functions of ISO packaging of Cisco NCS 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for the Cisco 8000 Series Routers could allow an authenticated, local attacker with administrator privileges to execute unsigned code during the installation of an ISO on an affected device.

  The vulnerability is due to an unsigned script within the ISO that is not verified during system upgrade before it is executed. To exploit this vulnerability, an attacker could modify an ISO image and then either use that image to upgrade as an authenticated administrator or place that image on a file server, which an unsuspecting administrator could then use when upgrading the device. A successful exploit could allow the attacker to execute arbitrary code on the affected device.

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

  Bug ID(s): CSCvr07463
  CVE ID: CVE-2021-1244
  Security Impact Rating (SIR): High
  CVSS Base Score: 6.7
  CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Workarounds

• There are no workarounds that address these vulnerabilities.

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 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

  The following table shows the first fixed release for each CVE ID:

  Affected Platform	First Fixed Release for CVE-2021-1136 (CSCvs70887)	First Fixed Release for CVE-2021-1244 (CSCvr07463)
  Cisco 8000 Series Routers	7.0.12 7.2.1	7.0.14 7.2.1
  Cisco NCS 540 Series Routers	7.2.1	7.1.2 7.2.1

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 internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ioxr-l-zNhcGCBt

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2021-FEB-03

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