Cisco NX-OS Software Bash Shell Role-Based Access Control Bypass Privilege Escalation Vulnerability

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Updated:March 6, 2019
Document ID:1551888529896959

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Cisco Security Advisory

Cisco NX-OS Software Bash Shell Role-Based Access Control Bypass Privilege Escalation Vulnerability

High
Advisory ID:
cisco-sa-20190306-nx-os-bash-escal
First Published:
2019 March 6 16:00 GMT
Version 1.0:
Final
Workarounds:
No workarounds available
CVE-2019-1593
CWE-264
CVSS Score:
Base 7.8Click Icon to Copy Verbose Score
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X
CVE-2019-1593
CWE-264

Summary

  • A vulnerability in the Bash shell implementation for Cisco NX-OS Software could allow an authenticated, local attacker to escalate their privilege level by executing commands authorized to other user roles. The attacker must authenticate with valid user credentials.

    The vulnerability is due to the incorrect implementation of a Bash shell command that allows role-based access control (RBAC) to be bypassed. An attacker could exploit this vulnerability by authenticating to the device and entering a crafted command at the Bash prompt. A successful exploit could allow the attacker to escalate their privilege level by executing commands that should be restricted to other roles. For example, a dev-ops user could escalate their privilege level to admin with a successful exploit of this vulnerability.

    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-20190306-nx-os-bash-escal

    This advisory is part of the March 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication, which includes 25 Cisco Security Advisories that describe 26 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: March 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

Affected Products

  • Vulnerable Products

    This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco NX-OS Software:

    • Nexus 3000 Series Switches
    • Nexus 3500 Platform Switches
    • Nexus 3600 Platform Switches
    • Nexus 7000 Series Switches
    • Nexus 7700 Series Switches
    • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
    • Nexus 9000 Series Switches in standalone NX-OS mode
    • Nexus 9500 R-Series Line Cards and Fabric Modules

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

    Determining the Cisco NX-OS Software Release

    Administrators can check the release of Cisco NX-OS Software that is running on a device by using the show version command in the device CLI. The following example shows the output of this command on a device that is running Cisco NX-OS Software Release 7.0(3)I5(1):

    nxos-switch# show version
Cisco Nexus Operating System (NX-OS) Software
TAC support: http://www.cisco.com/tac
Copyright (C) 2002-2016, Cisco and/or its affiliates.
All rights reserved.
The copyrights to certain works contained in this software are
owned by other third parties and used and distributed under their own
licenses, such as open source.  This software is provided "as is," and
unless otherwise stated, there is no warranty, express or implied, 
including but not limited to warranties of merchantability and fitness 
for a particular purpose. Certain components of this software are 
licensed under the GNU General Public License (GPL) version 2.0 or 
GNU General Public License (GPL) version 3.0  or the GNU
Lesser General Public License (LGPL) Version 2.1 or 
Lesser General Public License (LGPL) Version 2.0. 
A copy of each such license is available at
http://www.opensource.org/licenses/gpl-2.0.php and
http://opensource.org/licenses/gpl-3.0.html and
http://www.opensource.org/licenses/lgpl-2.1.php and
http://www.gnu.org/licenses/old-licenses/library.txt.
Software
  BIOS: version 07.57
  NXOS: version 7.0(3)I5(1) [build 7.0(3)I5(0.9)]
  BIOS compile time:  06/29/2016
  NXOS image file is: bootflash:///nxos.7.0.3.I5.0.9.bin
  NXOS compile time:  8/1/2016 23:00:00 [08/02/2016 00:30:32]
  .
  .
  .

    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:

    • Firepower 2100 Series Firewalls
    • Firepower 4100 Series Next-Generation Firewalls
    • Firepower 9300 Security Appliance
    • MDS 9000 Series Multilayer Switches
    • Nexus 1000V Switch for Microsoft Hyper-V
    • Nexus 1000V Switch for VMware vSphere
    • Nexus 2000 Series Fabric Extenders
    • Nexus 5500 Platform Switches
    • Nexus 5600 Platform Switches
    • Nexus 6000 Series Switches
    • UCS 6200 Series Fabric Interconnects
    • UCS 6300 Series Fabric Interconnects
    • UCS 6400 Series Fabric Interconnects

Details

  • In addition to the NX-OS CLI, Cisco NX-OS Software can support access to the Bash shell, which interprets commands that a user enters or that are read from a shell script. Bash enables access to and is used to manage the underlying Linux system on the device. In Cisco NX-OS Software, the Bash shell is accessible from user accounts that are associated with the Cisco NX-OS dev-ops role or the Cisco NX-OS network-admin role.

    For additional information, customers can refer to the Bash chapter of the Cisco NX-OS Programmability Guide.

Indicators of Compromise

  • Successful exploitation of this vulnerability could result in a user without authorization making NX-OS device configuration changes. As part of best practices, administrators can use the show accounting log command and monitor for unexpected configuration modifications. A configuration change would be done within the Bash shell, and a typical logging entry would follow this format:
    type=update:id=console0:user=root:cmd=configure terminal ; feature nxapi (SUCCESS)

Workarounds

  • There are no workarounds that address this vulnerability.

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

    Customers are advised to upgrade to an appropriate release as indicated in the applicable table in this section. To help ensure a complete upgrade solution, customers should consider that this advisory is part of a bundled publication. The following page provides a complete list of bundle advisories: Cisco Event Response: March 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

    In the following tables, the left column lists releases of Cisco FXOS Software or Cisco NX-OS Software. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

    Although the releases listed in the right column of each table include fixes for the vulnerabilities, the fix related to the Cisco NX-OS Software Image Signature Verification Vulnerability requires a BIOS upgrade as part of the software upgrade. Customers who are upgrading the software for any of the following products are advised to refer to this advisory for further details about the BIOS upgrade and affected product IDs and BIOS versions:

    • Nexus 3000 Series Switches
    • Nexus 9000 Series Fabric Switches in ACI mode
    • Nexus 9000 Series Switches in standalone NX-OS mode
    • Nexus 9500 R-Series Line Cards and Fabric Modules

    Nexus 3000 Series Switches: CSCvj59431

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    Prior to 7.0(3)I2(1)
    		 Not vulnerable
    		 7.0(3)I7(6)
    7.0(3)I4 7.0(3)I4(9) 7.0(3)I7(6)
    7.0(3)I5 7.0(3)I7(4) 7.0(3)I7(6)
    7.0(3)I6 7.0(3)I7(4) 7.0(3)I7(6) 
    7.0(3)I7 7.0(3)I7(4) 7.0(3)I7(6) 
    9.2 Not vulnerable
    		 9.2(2)

    Nexus 3500 Platform Switches: CSCvj59431

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    Prior to 6.0(2)A8
    		 Not vulnerable
    		 6.0(2)A8(11) 
    6.0(2)A8 Not vulnerable  6.0(2)A8(11) 
    7.0(3) 7.0(3)I7(4) 7.0(3)I7(6) 
    9.2 Not vulnerable 9.2(2)

    Nexus 3600 Platform Switches: CSCvk52941

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    7.0(3)
    		 7.0(3)F3(3c)1 7.0(3)F3(5) 
    9.2 Not vulnerable 9.2(2)
    1This vulnerability is not fixed in 7.0(3)F3(4) but is fixed in 7.0(3)F3(5).

    Nexus 7000 and 7700 Series Switches: CSCvj59446

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    6.2
    		 Not vulnerable  6.2(22)
    7.2 Not vulnerable  6.2(22) 
    7.3 Not vulnerable  8.2(3) 
    8.0 Not vulnerable 8.2(3)
    8.11 8.2(3) 8.2(3)
    8.2 8.2(3) 8.2(3) 
    8.3 8.3(1) 8.3(2)
    1The Nexus 7000 and 7700 Series Switches did not support Bash until the 8.1 software release.

    Nexus 9000 Series Fabric Switches in ACI Mode: CSCvk52940

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    Prior to 13.1
    		 13.2(4d) 14.0(3d)
    13.1
    		 13.2(4d) 14.0(3d)
    13.2
    		 13.2(4d) 14.0(3d)
    14.0 14.0(1h)
    		 14.0(3d)

    Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvj59431

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    Prior to 7.0(3)I2(1)
    		 Not vulnerable
    		 7.0(3)I7(6) 
    7.0(3)I4 7.0(3)I4(9) 7.0(3)I7(6)
    7.0(3)I5 7.0(3)I7(4) 7.0(3)I7(6) 
    7.0(3)I6 7.0(3)I7(4) 7.0(3)I7(6) 
    7.0(3)I7 7.0(3)I7(4) 7.0(3)I7(6)
    9.2 Not vulnerable 9.2(2)

    Nexus 9500 R-Series Line Cards and Fabric Modules: CSCvk52941

    Cisco NX-OS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    7.0(3)
    		 7.0(3)F3(3c)1 7.0(3)F3(5)
    9.2 Not vulnerable 9.2(2)
    1This vulnerability is not fixed in 7.0(3)F3(4) but is fixed in 7.0(3)F3(5).

    Additional Resources

    For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, administrators can refer to the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

    Cisco MDS Series Switches
    Cisco Nexus 1000V for VMware Switch
    Cisco Nexus 3000 Series and 3500 Series Switches
    Cisco Nexus 5000 Series Switches
    Cisco Nexus 5500 Platform Switches
    Cisco Nexus 6000 Series Switches
    Cisco Nexus 7000 Series Switches
    Cisco Nexus 9000 Series Switches
    Cisco Nexus 9000 Series ACI-Mode Switches

    For help determining the best Cisco NX-OS Software release for Cisco UCS, refer to the Recommended Releases documents in the release notes for the device.

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.

Cisco Security Vulnerability Policy

  • 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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Revision History

  • Version Description Section Status Date
    1.0 Initial public release. — Final 2019-March-06
    Show Less

Cisco Security Vulnerability Policy

  • 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.

Subscribe to Cisco Security Notifications

Related to This Advisory