Cisco FXOS and NX-OS Software Cisco Fabric Services Denial of Service Vulnerability

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Updated:August 26, 2020
Document ID:1598459880963456

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Cisco Security Advisory

Cisco FXOS and NX-OS Software Cisco Fabric Services Denial of Service Vulnerability

High
Advisory ID:
cisco-sa-fxos-nxos-cfs-dos-dAmnymbd
First Published:
2020 August 26 16:00 GMT
Last Updated: 
2020 August 26 21:23 GMT
Version 1.1:
Final
Workarounds:
No workarounds available
CVE-2020-3517
CWE-476
CVSS Score:
Base 8.6Click Icon to Copy Verbose Score
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
CVE-2020-3517
CWE-476

Summary

  • A vulnerability in the Cisco Fabric Services component of Cisco FXOS Software and Cisco NX-OS Software could allow an unauthenticated attacker to cause process crashes, which could result in a denial of service (DoS) condition on an affected device. The attack vector is configuration dependent and could be remote or adjacent. For more information about the attack vector, see the Details section of this advisory. 

    The vulnerability is due to insufficient error handling when the affected software parses Cisco Fabric Services messages. An attacker could exploit this vulnerability by sending malicious Cisco Fabric Services messages to an affected device. A successful exploit could allow the attacker to cause a reload of an affected device, which could result in a DoS condition. 

    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-fxos-nxos-cfs-dos-dAmnymbd

    This advisory is part of the August 2020 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication, which includes seven Cisco Security Advisories that describe seven vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: August 2020 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 FXOS or NX-OS Software and have Cisco Fabric Services enabled:

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

    Determine Whether a Device Has Cisco Fabric Services Enabled

    To determine whether a device that is running Cisco FXOS or NX-OS Software has Cisco Fabric Services enabled, use the show cfs status | include Distribution command. If the command returns a global Distribution state of Enabled, the device is vulnerable. If the global Distribution state is Disabled or this command is not available, the device is not affected by this vulnerability. The following example shows the output of the show cfs status | include Distribution command from a device that is vulnerable:

    nexus# show cfs status | include Distribution
    Distribution : Enabled
    Distribution over IP : Enabled
    Distribution over Ethernet : Disabled
    nexus#

    Note: On Cisco UCS Fabric Interconnects, first execute the connect nxos command to enter the NX-OS CLI, then use the show cfs status | include Distribution command.

    For more information about Cisco Fabric Services and its distribution status, see the Details 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 1000 Series
    • Firepower 2100 Series
    • Nexus 1000 Virtual Edge for VMware vSphere
    • Nexus 1000V Switch for Microsoft Hyper-V
    • Nexus 1000V Switch for VMware vSphere
    • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode

Details

  • Cisco Fabric Services provides a common infrastructure for distributing and synchronizing configuration data between Cisco devices that are on the same network and with virtual port channels (vPCs) or in Virtual Extensible LAN (VXLAN) deployments. This includes configuration data for applications and features that are compatible with and enabled to use Cisco Fabric Services—for example, Distributed Device Alias Services, Network Time Protocol (NTP), and user and administrator roles.

    The vulnerability that is described in this advisory is due to insufficient error handling when the affected software parses Cisco Fabric Services messages. Exploitation of this vulnerability does not require any applications to be enabled to use Cisco Fabric Services. Instead, exploitation depends on which Cisco Fabric Services distribution types are configured for a device. In addition, the attack vectors vary based on which distribution types are configured. If a device is enabled to use more than one distribution type, the applicable attack vectors for all those distribution types exist for the device.

    Cisco Fabric Services over Fibre Channel

    Distribution Distributes data over a Fibre Channel, such as a virtual storage area network (VSAN)
    Enablement Enabled by default on Cisco MDS 9000 Series Multilayer Switches

    Enabled on Nexus devices if Fibre Channel or Fibre Channel over Ethernet (FCoE) configuration is present
    Attack Vector Attack could occur over Fibre Channel, Fibre Channel over Ethernet (FCoE), or Fibre Channel over IP (FCIP)

    Attack could succeed in the data plane, not the management plane, of any Fibre Channel port

    If no Fibre Channel and no FCoE ports are configured for a device, this distribution type cannot be used to exploit the vulnerability
    CVSS Attack Vector Adjacent
     

    Cisco Fabric Services over Ethernet

    Distribution Distributes data over an Ethernet network
    Enablement Disabled by default
    Attack Vector Attack is possible from only a vPC peer or an attacker who has access to a vPC peer link

    No other peer, neighbor, or network node can be used to exploit the vulnerability
    CVSS Attack Vector Adjacent
     

    Cisco Fabric Services over IP

    Distribution Distributes data over an IPv4 or IPv6 network
    Enablement Disabled by default
    Attack Vector Attack is possible from any node that has IP network connectivity to the management interface of a device

    Attack cannot succeed from the data plane
    CVSS Attack Vector Network
     

    Determine the Distribution Status of Cisco Fabric Services

    To display configuration information and check the distribution status of Cisco Fabric Services for a device, use the show cfs status | include Distribution command in the device CLI, as shown in the following example:

    switch# show cfs status | include Distribution
    Distribution : Enabled
    Distribution over IP : Disabled
    Distribution over Ethernet : Disabled

    In the preceding example, the Enabled value in the Distribution field of the command output indicates that Cisco Fabric Services is enabled for the device and that the device is configured to use the default Cisco Fabric Services distribution type, which is Cisco Fabric Services over Fibre Channel. The Disabled value in the Distribution over IP field and the Distribution over Ethernet field indicates that the device is not additionally configured to use the Cisco Fabric Services over IP or Cisco Fabric Services over Ethernet distribution types.

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 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.

    Cisco FXOS Software

    In the following table(s), the left column lists Cisco software releases. 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.

    Firepower 4100 Series and Firepower 9300 Security Appliances1

    Cisco FXOS Software Release First Fixed Release for This Vulnerability First Fixed Release for all Vulnerabilities Described in the Bundle of Advisories
    1.1 1.1.4.179 1.1.4.179
    2.0 2.0.1.153 2.0.1.153
    2.1 2.1.1.86 2.1.1.86
    2.2 2.2.1.70 2.2.1.70
    2.3 Not vulnerable Not vulnerable
    2.4 Not vulnerable Not vulnerable
    2.6 Not vulnerable Not vulnerable
    2.7 Not vulnerable Not vulnerable
    2.8 Not vulnerable Not vulnerable

    1. This vulnerability does not affect releases of Cisco FXOS Software that have the fix for the Cisco FXOS and NX-OS Software Cisco Fabric Services Arbitrary Code Execution Vulnerability, which essentially removed support for Cisco Fabric Services from Cisco FXOS Software.

    Cisco NX-OS Software

    To help customers determine their exposure to vulnerabilities in Cisco NX-OS Software, Cisco provides the Cisco Software Checker to identify any Cisco Security Advisories that impact a specific Cisco NX-OS Software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).

    Customers can use the Cisco Software Checker to search advisories in the following ways:

    • Choose the software, platform, and one or more releases
    • Upload a .txt file that includes a list of specific releases
    • Enter the output of the show version command

    After initiating a search, customers can customize the search to include all Cisco Security Advisories or one or more specific advisories.

    Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by choosing the Cisco NX-OS Software and platform and then entering a release—for example, 7.0(3)I7(5) for Cisco Nexus 3000 Series Switches or 14.0(1h) for Cisco NX-OS Software in ACI mode:

     

    By default, the Cisco Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, customers can use the Cisco Software Checker and check the Medium check box in the drop-down list under Impact Rating when customizing a search.

    Cisco Nexus 3000 and 9000 Series Switches Software Maintenance Upgrade

    For Cisco Nexus 3000 and 9000 Series Switches, the following software maintenance upgrade (SMU) is available for Cisco NX-OS Software Release 7.0(3)I7(8): nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm.

    To download the SMU from the Software Center on Cisco.com, do the following:

    1. Click Browse All.
    2. Choose IOS and NX-OS Software > NX-OS > NX-OS Software > Switches > Data Center Switches.
    3. Choose the appropriate product and model.
    4. Choose NX-OS Software Maintenance Upgrades (SMU).
    5. Choose Release 7.0(3)I7(8) from the left pane of the appropriate product page.

    Note: The SMU filename is nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm.

    SMU Installation Instructions

    To install the SMU, copy the SMU to the Bootflash: file system for the switch and execute the following commands, which activate the fix right away (this is a hot patch):

    1. install add bootflash:nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm activate
    2. install commit

    The following example shows the commands for installing the SMU for Cisco NX-OS Software Release 7.0(3)I7(8):

    nx-os# install add bootflash:nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm activate  nx-os# install commit

    Note: These instructions apply to only this particular type of SMU.

    Cisco UCS Software

    In the following table(s), the left column lists Cisco software releases. 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.

    UCS 6200, 6300, and 6400 Series Fabric Interconnects

    Cisco UCS Software Release First Fixed Release for This Vulnerability First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
    Earlier than 3.2 Migrate to a fixed release. Migrate to a fixed release.
    3.2 3.2(3o) 3.2(3o)
    4.0 4.0(4i) 4.0(4i)
    4.1 4.1(1c) 4.1(1c)
     

    Additional Resources

    For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, see 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 Switches
    Cisco Nexus 5500 Platform Switches
    Cisco Nexus 5600 Platform Switches
    Cisco Nexus 6000 Series Switches
    Cisco Nexus 7000 Series Switches
    Cisco Nexus 9000 Series Switches
    Cisco Nexus 9000 Series ACI-Mode Switches

    To determine the best release for Cisco UCS Software, see 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
    1.1 Fixed Software Checker link. Fixed Software Final 2020-AUG-26
    1.0 Initial public release. — Final 2020-AUG-26
    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