Summary

• A vulnerability in the access-control logic of the NETCONF over Secure Shell (SSH) of Cisco IOS XR Software may allow connections despite an access control list (ACL) that is configured to deny access to the NETCONF over SSH of an affected device.

  The vulnerability is due to a missing check in the NETCONF over SSH access control list (ACL). An attacker could exploit this vulnerability by connecting to an affected device using NETCONF over SSH. A successful exploit could allow the attacker to connect to the device on the NETCONF port. Valid credentials are required to access the device. This vulnerability does not affect connections to the default SSH process on the device.

  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-20191120-iosxr-ssh-bypass

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco IOS XR Software releases 6.5.1, 6.5.2, and 6.5.3. This vulnerability does not affect any other releases.

  See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  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 Cisco IOS Software or Cisco IOS XE Software.

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• 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.

  Fixed Releases

  At the time of publication, Cisco IOS XR Software Release 6.5.3 with SMU and later contained the fix for this vulnerability.

  See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  Customers can download the SMU from the Software Center by doing the following:

  1. Click Browse all.
  2. Choose Routers > Service Provider Edge Routers.
  3. Choose the specific router family from the right pane of the product selector.
  4. Choose a specific product from the right pane of the product selector.
  5. Choose Software on Chassis > IOS XR Software Maintenance Upgrades (SMU) - 6.5.3.
  6. Click the download link for the Hitless/Optional SMU, ACL under 'ssh server netconf' did not take effect release.

  If the SMU is not listed for your required platform, contact your account team or the Cisco TAC to request an SMU for your platform.

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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191120-iosxr-ssh-bypass

Revision History

• Version	Description	Section	Status	Date
  1.1	Clarified affected releases. Added instructions for requesting an SMU.	Vulnerable Products and Fixed Releases	Final	2019-November-23
  1.0	Initial public release.	-	Final	2019-November-20

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