Headline
CVE-2020-3517: Cisco Security Advisory: Cisco FXOS and NX-OS Software Cisco Fabric Services Denial of Service Vulnerability
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.
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.
**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 ifover 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.
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.htmlAdditionally, 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. 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.
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:
- Click Browse All.
- Choose IOS and NX-OS Software > NX-OS > NX-OS Software > Switches > Data Center Switches.
- Choose the appropriate product and model.
- Choose NX-OS Software Maintenance Upgrades (SMU).
- 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 , 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):
- install add activate
- 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.