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AUSCERT External Security Bulletin Redistribution
Cisco NX-OS Software Unexpected IP in IP Packet Processing Vulnerability
2 June 2020
AusCERT Security Bulletin Summary
Product: Cisco NX-OS Software
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Unauthorised Access -- Remote/Unauthenticated
CVE Names: CVE-2020-10136
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Cisco NX-OS Software Unexpected IP in IP Packet Processing Vulnerability
Advisory ID: cisco-sa-nxos-ipip-dos-kCT9X4
First Published: 2020 June 1 16:00 GMT
Version 1.0: Final
o A vulnerability in the network stack of Cisco NX-OS Software could allow an
unauthenticated, remote attacker to bypass certain security boundaries or
cause a denial of service (DoS) condition on an affected device.
The vulnerability is due to the affected device unexpectedly decapsulating
and processing IP in IP packets that are destined to a locally configured
IP address. An attacker could exploit this vulnerability by sending a
crafted IP in IP packet to an affected device. A successful exploit could
cause the affected device to unexpectedly decapsulate the IP in IP packet
and forward the inner IP packet. This may result in IP packets bypassing
input access control lists (ACLs) configured on the affected device or
other security boundaries defined elsewhere in the network.
Under certain conditions, an exploit could cause the network stack process
to crash and restart multiple times, leading to a reload of the affected
device and a DoS condition.
Cisco has released software updates that address this vulnerability. There
are workarounds that address this vulnerability.
This advisory is available at the following link:
o Vulnerable Products
This vulnerability affects the following Cisco products if they are running
a vulnerable release of Cisco NX-OS Software:
Nexus 1000 Virtual Edge for VMware vSphere ( CSCvu10050 )
Nexus 1000V Switch for Microsoft Hyper-V ( CSCvt67738 )
Nexus 1000V Switch for VMware vSphere ( CSCvt67738 )
Nexus 3000 Series Switches ( CSCun53663 ) ^ 1
Nexus 5500 Platform Switches ( CSCvt67739 )
Nexus 5600 Platform Switches ( CSCvt67739 )
Nexus 6000 Series Switches ( CSCvt67739 )
Nexus 7000 Series Switches ( CSCvt66624 )
Nexus 9000 Series Switches in standalone NX-OS mode ( CSCun53663 ) ^ 1
UCS 6200 Series Fabric Interconnects ( CSCvu03158 )
UCS 6300 Series Fabric Interconnects ( CSCvt67740 )
^ 1 Only a limited set of releases for Nexus 3000 Series and Nexus 9000
Series Switches is affected by this vulnerability. Details are available in
the Cisco Software Checker as described in the Fixed Software section of
It is not required to have an IP in IP tunnel interface configured on the
device in order to be affected by this vulnerability. Cisco UCS Fabric
Interconnects are affected only when NetFlow monitoring is enabled on the
device and a flow exporter profile is configured with a source IP address
set for the exporter interface. For details about NetFlow configuration for
Cisco UCS Fabric Interconnects, see the NetFlow Monitoring section of the
Cisco UCS Manager System Monitoring Guide .
For information about which Cisco 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
Firepower 1000 Series
Firepower 2100 Series
Firepower 4100 Series
Firepower 9300 Security Appliances
MDS 9000 Series Multilayer Switches
Nexus 9000 Series Fabric Switches in Application Centric Infrastructure
UCS 6400 Series Fabric Interconnects
o RFC 2003 specifies a method to encapsulate an IPv4 datagram within another
IPv4 datagram. The IP protocol number 4 is used to indicate that the
payload within a carrier IP packet is a passenger IPv4 packet.
Multiple Cisco products running Cisco NX-OS Software support IP in IP
packet encapsulation and decapsulation when a tunnel interface is manually
configured on the device using tunnel mode ipip and appropriate tunnel
source and tunnel destination . The device is not expected to decapsulate
and process any IP in IP traffic that is not destined to such a tunnel
This vulnerability causes an affected device to unexpectedly decapsulate
and process IP in IP packets that are destined to a locally configured IP
address, even when no tunnel configuration is present. Any input ACL
configured on an inbound interface of the affected device is evaluated
against the IP fields on the carrier IP packet prior to decapsulation; it
would not be evaluated on the passenger IP packet. This may result in the
passenger IP packet bypassing the intended ACL filtering. This may also
allow the passenger IP packet to bypass other security boundaries that
might be defined in the network path to the affected device in the presence
of network filtering techniques that only inspect the outer IP header and
not the inner IP packet.
Under specific conditions, processing of a crafted IP in IP packet could
cause the network stack process to crash on an affected device. Repeated
exploitation that causes the network stack process to restart multiple
times could lead to a reload of the affected device, resulting in a DoS
condition. A crash of the network stack process is followed by creation of
a netstack core file on the device, which can be viewed by using the show
cores CLI command (or dir cores on the local-mgmt CLI for Cisco UCS Fabric
Interconnects). If a netstack core file is present, customers are advised
to contact the Cisco Technical Assistance Center (TAC) to review the file
and determine whether this vulnerability has been exploited on the device.
This vulnerability can only be triggered by IP in IP traffic that is
destined to an affected device and cannot be exploited using traffic that
transits an affected device. The vulnerability can only be triggered by IP
in IP packets on which both the carrier and the passenger datagrams are
IPv4. It cannot be triggered when either carrier, passenger, or both
carrier and passenger are IPv6 datagrams, nor can it be triggered by any
other tunneling protocol, including but not limited to Generic Routing
o Using infrastructure access control lists (iACLs) to allow only strictly
required management and control plane traffic that is destined to the
affected device, as recommended in the Cisco Guide to Securing NX-OS
Software Devices , would prevent exploitation of this issue on Nexus
devices. Customers may also consider explicitly denying all IP packets with
protocol number 4 (corresponding to IP in IP packets) as part of their
iACLs, if no legitimate IP in IP traffic is used in their network. A
customized control plane policing (CoPP) policy may also be used to drop IP
in IP traffic that is destined to an affected device; however, support for
CoPP customization varies across different Nexus platforms and software
releases. Customers are advised to contact their support organization for
any assistance required with evaluating the feasibility of a workaround and
with implementing a workaround on an affected device.
Exploitation of this issue on Cisco UCS Fabric Interconnects is only
possible if NetFlow monitoring is enabled on an affected device. Customers
who do not have a strict requirement of using NetFlow monitoring may
evaluate the possibility of disabling it until they can perform a software
upgrade to a fixed release.
Customers should first evaluate the impact of configuration changes to the
device and their security policy. Customers concerned about undesired or
unexpected side effects should consult with their support organization
before implementing any configuration change.
o 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/
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
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
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
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
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:
[Cisco NX-OS Software ] [MDS 9000 Series Multilayer Switches]
[ ] [Check]
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 7000 Series Switches SMUs
For Cisco Nexus 7000 Series Switches, software maintenance upgrades (SMUs)
are available for Cisco NX-OS Software Release 7.3(6)D1(1). Customers can
download the following SMUs from the Software Center on Cisco.com:
For details about downloading and installing SMUs in Cisco NX-OS Software
for Cisco Nexus 7000 Series Switches, see the Performing Software
Maintenance Upgrades section of the Cisco Nexus 7000 Series NX-OS System
Management Configuration Guide .
Cisco UCS Software
In the following table(s), the left column lists Cisco software releases,
and the right column indicates whether a release was affected by the
vulnerability described in this advisory and which release included the fix
for this vulnerability.
UCS 6200 and 6300 Series Fabric Interconnects:
Cisco UCS Software Release First Fixed Release for This Vulnerability
Earlier than 3.2 3.2(3o)
4.0 4.0(4i) (June 2020)
4.1 4.1(1d) (June 2020)
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 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, see the Recommended Releases
documents in the release notes for the device.
Exploitation and Public Announcements
o 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.
o Cisco would like to thank Yannay Livneh for reporting this vulnerability.
Cisco Security Vulnerability Policy
o 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.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2020-JUN-01 |
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