Summary

• A vulnerability in the Bash shell implementation for Cisco NX-OS Software could allow an authenticated, local attacker to bypass the limited command set of the restricted Guest Shell and execute commands at the privilege level of a network-admin user outside of the Guest Shell. The attacker must authenticate with valid administrator device credentials.

  The vulnerability is due to the incorrect implementation of a CLI command that allows a Bash command to be incorrectly invoked on the Guest Shell CLI. An attacker could exploit this vulnerability by authenticating to the device and entering a crafted command at the Guest Shell prompt. A successful exploit could allow the attacker to issue commands that should be restricted by a Guest Shell account.

  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-20190515-nxos-bash-bypass

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 Switches in standalone NX-OS mode
  • Nexus 9500 R-Series Switching Platform

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

  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
  • Firepower 4100 Series
  • Firepower 9300 Security Appliances
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • Nexus 5500 Platform Switches
  • Nexus 5600 Platform Switches
  • Nexus 6000 Series Switches
  • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
  • 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.

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

  No upgrade action is necessary for customers who have already applied a recommended release to address the March 2019 Cisco FXOS and NX-OS Software bundle. See Cisco Event Response: March 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication for a list of advisories in the bundle.

  Customers who have not applied a recommended release to address the March 2019 bundle are advised to upgrade to an appropriate release as indicated in the applicable table in this section. In the following tables, the left column lists Cisco NX-OS Software releases. The right column indicates the first release that includes the fix for this vulnerability.

  Nexus 3000 Series Switches, Nexus 3500 Platform Switches, and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvh76090

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Prior to 7.0(3)I2	Not vulnerable
  7.0(3)I4	7.0(3)I4(9)
  7.0(3)I7	7.0(3)I7(4)
  9.2(1)	Not vulnerable

  Nexus 3600 Platform Switches and Nexus 9500 R-Series Switching Platform: CSCvj01497

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  7.0(3)	7.0(3)F3(5)
  9.2	Not vulnerable

  Nexus 7000 and 7700 Series Switches: CSCvj01472

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Prior to 6.2	Not vulnerable
  6.2	Not vulnerable
  7.2	Not vulnerable
  7.3	Not vulnerable
  8.0	Not vulnerable
  8.1	8.2(3)
  8.2	8.2(3)
  8.3	8.3(1)

  
  

  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.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190515-nxos-bash-bypass

Revision History

• Version	Description	Section	Status	Date
  1.1	Update the N7K fixed release table.	Fixed Software	Final	2019-May-20
  1.0	Initial public release.	-	Final	2019-May-15

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