Cisco Security Advisory
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CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X
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A vulnerability in the Cisco Discovery Protocol implementation for Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to execute arbitrary code or cause a reload on an affected device.
The vulnerability is due to improper validation of string input from certain fields in Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. A successful exploit could allow the attacker to cause a stack overflow, which could allow the attacker to execute arbitrary code with administrative privileges on an affected device.
Note: Cisco Discovery Protocol is a Layer 2 protocol. To exploit this vulnerability, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent).
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-20200205-iosxr-cdp-rce
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Vulnerable Products
This vulnerability affects the following Cisco products if they have Cisco Discovery Protocol enabled both globally and on at least one interface and if they are running a vulnerable release of Cisco IOS XR Software (32-bit or 64-bit):
- ASR 9000 Series Aggregation Services Routers
- Carrier Routing System (CRS)
- IOS XRv 9000 Router
- Network Convergence System (NCS) 540 Series Routers
- Network Convergence System (NCS) 560 Series Routers
- Network Convergence System (NCS) 1000 Series Routers
- Network Convergence System (NCS) 5000 Series Routers
- Network Convergence System (NCS) 5500 Series Routers
- Network Convergence System (NCS) 6000 Series Routers
This vulnerability also affects third-party white box routers if they have Cisco Discovery Protocol enabled both globally and on at least one interface and if they are running a vulnerable release of Cisco IOS XR Software.
Note: Cisco Discovery Protocol is not enabled in Cisco IOS XR Software by default.
For information about which Cisco IOS XR Software releases are vulnerable, see the Fixed Software section of this advisory.
Determine the Status of Cisco Discovery Protocol
Administrators can determine whether Cisco Discovery Protocol is enabled on a device by using the show running-config | include cdp command in the device CLI. If the command returns at least the following lines, Cisco Discovery Protocol is enabled globally and on at least one interface:
RP/0/RP0/CPU0:ios##show running-config | include cdp Mon Dec 2 17:00:27.921 UTC Building configuration... cdp cdp . . .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 Network Convergence System (NCS) 520 Series Routers. Cisco has also confirmed that this vulnerability does not affect the following Cisco software:
- FXOS Software
- IOS Software
- IOS XE Software
- NX-OS Software
- UCS Software
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There are no workarounds that address this vulnerability.
However, customers who do not use the Cisco Discovery Protocol feature can disable it either globally to fully close the attack vector or on individual interfaces to reduce the attack surface.
Disable Cisco Discovery Protocol Globally
To disable Cisco Discovery Protocol globally on devices that are running Cisco IOS XR Software, administrators can use the no cdp command in global configuration mode, as shown in the following example:
RP/0/RP0/CPU0:ios#conf t Mon Dec 2 17:58:08.556 UTC RP/0/RP0/CPU0:ios(config)#no cdp RP/0/RP0/CPU0:ios(config)#exit
Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]:yesDisable Cisco Discovery Protocol on an Interface
To disable Cisco Discovery Protocol on an interface on devices that are running Cisco IOS XR Software, administrators can use the no cdp command in interface configuration mode, as shown in the following example:
RP/0/RP0/CPU0:ios#conf t Mon Dec 2 18:00:08.622 UTC RP/0/RP0/CPU0:ios(config)#interface GigabitEthernet0/0/0/0 RP/0/RP0/CPU0:ios(config-if)#no cdp RP/0/RP0/CPU0:ios(config-if)#end Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]:yes
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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 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.
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.htmlCustomers 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 vulnerability described in this advisory and the first release that includes the fix for this vulnerability.
Cisco IOS XR Software Release First Fixed Release for This Vulnerability Earlier than 6.6 Appropriate SMU 6.61 6.6.3 or appropriate SMU 7.0 7.0.2 (Mar 2020) or appropriate SMU 7.1 Not vulnerable 1. Customers who are running Cisco IOS XR Software Release 6.6 on white box routers are advised to upgrade to Release 6.6.12 and then install the software maintenance upgrade (SMU). Customers who are running Cisco IOS XR Software Release 6.6 on other platforms are advised to upgrade to Release 6.6.3.
The following SMUs are also available for Cisco IOS XR Software:
Cisco IOS XR Software Release Platform SMU Name 5.2.5 NCS6K ncs6k-5.2.5.CSCvr78185 6.4.2 ASR9K-PX asr9k-px-6.4.2.CSCvr78185 CRS-PX hfr-px-6.4.2.CSCvr78185 6.5.3 ASR9K-PX asr9k-px-6.5.3.CSCvr78185 ASR9K-X64 asr9k-x64-6.5.3.CSCvr78185 NCS540 ncs540-6.5.3.CSCvr78185 NCS5K ncs5k-6.5.3.CSCvr78185 NCS5500 ncs5500-6.5.3.CSCvr78185 XRV9K xrv9k-6.5.3.CSCvr78185 6.6.12 White box iosxrwbd-6.6.12.CSCvr78185 6.6.25 NCS560 ncs560-6.6.25.CSCvr78185 7.0.1 NCS540L ncs540l-7.0.1.CSCvr78185 For details on where to download and how to install SMUs in Cisco IOS XR Software, see the IOS XR Software Maintenance Updates (SMUs) guide.
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In October 2020, the Cisco Product Security Incident Response Team (PSIRT) received reports of attempted exploitation of this vulnerability in the wild. Cisco recommends that customers upgrade to a fixed Cisco IOS XR Software release to remediate this vulnerability.
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Cisco would like to thank Barak Hadad of Armis for reporting this vulnerability.
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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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Show LessVersion Description Section Status Date 1.1 Updated Exploitation and Public Announcements to indicate that exploitation in the wild has been observed. Fixed two typos in Vulnerable Products (no change to affected products). Exploitation and Public Announcements and Vulnerable Products Final 2020-OCT-20 1.0 Initial public release. — Final 2020-FEB-05
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