Summary

• A vulnerability in Cisco Network Services Orchestrator (NSO) could allow an authenticated, local attacker to execute arbitrary commands at the level of the account under which Cisco NSO is running, which is root by default. To exploit this vulnerability, an attacker must have a valid account on an affected device.

  The vulnerability exists because the affected software incorrectly runs the SFTP user service at the privilege level of the account that was running when the NSO built-in Secure Shell (SSH) server for CLI was enabled. If the NSO built-in SSH server was not enabled, the device is not affected by this vulnerability. An attacker with low-level privileges could exploit this vulnerability by authenticating to an affected device and issuing a series of commands at the SFTP interface. A successful exploit could allow the attacker to elevate privileges to the level of the account under which Cisco NSO is running, which is root by default.

  Note: Any user who can authenticate to the built-in SSH server may exploit this vulnerability. By default, all Cisco NSO users have this access if the server is enabled.

  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-nso-priv-esc-XXqRtTfT

Affected Products

• Vulnerable Products

  This vulnerability affects the following releases of Cisco NSO if the NSO built-in SSH server for CLI is enabled:

  • Releases 5.4 through 5.4.3.1
  • Releases 5.5 through 5.5.2.2
  • Releases 5.6 through 5.6.14
  • Releases 5.7 through 5.7.12
  • Releases 5.8 through 5.8.10
  • Releases 6.0 through 6.0.7
  • Releases 6.1 through 6.1.3

  The NSO built-in SSH server is disabled by default in an NSO system installation. To determine whether the built-in SSH server is enabled, navigate to the ncs.conf file, which is usually located under the /etc/ncs directory. The built-in SSH server is enabled if the value for SSH enabled is true, as shown in this example:

  < cli >
    < enabled >true< /enabled >
    < !-- Use the builtin SSH server -- >
    < ssh >
      < enabled >true< /enabled >
      < ip >0.0.0.0< /ip >
      < port >2024< /port >
    < /ssh >

  
  

  Products Confirmed Not Vulnerable

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

Workarounds

• There are no workarounds that address this vulnerability. However, a mitigation is available.

  Administrators can disable the NSO built-in SSH server and run the ncs_cli program as a login shell. For guidance on using the ncs_cli program, see NSO 5.5 User Guide: Starting the CLI.

  While this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

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

  In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.

  Cisco NSO Release	First Fixed Release
  5.4	5.4.3.2
  5.5	5.5.2.3
  5.6	5.6.14.1
  5.7	5.7.13
  5.8	5.8.11
  6.0	6.0.8
  6.1	6.1.3.1

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco 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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nso-priv-esc-XXqRtTfT

Revision History

• Version	Description	Section	Status	Date
  2.1	Corrected code example.	Vulnerable Products	Final	2023-OCT-25
  2.0	Updated information about vulnerable releases and fixed releases.	Vulnerable Products and Fixed Releases	Final	2023-OCT-04
  1.0	Initial public release.	-	Final	2021-AUG-04

  Show Less