Summary

• A vulnerability in the Border Gateway Protocol (BGP) Multiprotocol Label Switching (MPLS)-based Ethernet VPN (EVPN) implementation of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to trigger a denial of service (DoS) condition on an affected device.

  The vulnerability is due to a logic error that occurs when the affected software processes specific EVPN routing information. An attacker could exploit this vulnerability by injecting malicious traffic patterns into the targeted EVPN network.

  A successful exploit could result in a crash of the l2vpn_mgr process on Provider Edge (PE) device members of the same EVPN instance (EVI). On each of the affected devices, a crash could lead to system instability and the inability to process or forward traffic through the device, resulting in a DoS condition that would require manual intervention to restore normal operating conditions.

  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-20190515-iosxr-evpn-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS XR Software and are participating in a BGP MPLS-based EVI.

  Cisco has confirmed that this vulnerability affects both Cisco IOS XR 32-bit Software and Cisco IOS XR 64-bit Software.

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

  Determining Whether the Device Has a Vulnerable Configuration

  There are two methods for determining whether the device has a vulnerable configuration.

  Option 1: Using the show evpn evi | include EVPN command

  Administrators can use the show evpn evi | include EVPN command to determine whether the device is participating in a BGP MPLS-based EVI.

  The following example shows the output of the command for a device that is participating in a BGP MPLS-based EVI:

  RP/0/0/CPU0:Router#show evpn evi | i EVPN
  Tue May 14 09:40:09.277 EST
  

  VPN-ID     Encap     Bridge Domain                Type
  ---------- ------ ---------------------------- -------------------
     MPLS                           EVPN

  If this command does not exist, or if it produces an output that does not show the string EVPN within the Type column, the device is not affected by the vulnerability described in this advisory.

  Option 2: Using the show running-config formal l2vpn | include "l2vpn bridge group [^ ]+ bridge-domain [^ ]+ evi [0-9]+" command

  Administrators can use the show running-config formal l2vpn | include "l2vpn bridge group [^ ]+ bridge-domain [^ ]+ evi [0-9]+" command to determine whether the device is participating in a BGP MPLS-based EVI. The following example shows the output of the command for a device that is participating in a BGP MPLS-based EVI:

  RP/0/0/CPU0:Router#show running-config formal l2vpn | include "l2vpn bridge group [^ ]+ bridge-domain [^ ]+ evi [0-9]+"
  l2vpn bridge group  bridge-domain  evi 

  An empty output of this command indicates that the device is not affected by the vulnerability described in this advisory.

  Note: Some hardware/software combinations may not support the show running-config formal command. In that case, use the verification step indicated in Option 1.

  Determining the Cisco IOS XR Software Release

  To determine which Cisco IOS XR Software release is running on a device and the name of the device on which it is running, administrators can log in to the device and use the show version command in the CLI. If the device is running Cisco IOS XR Software or similar text appears in the system banner. The location and name of the system image file that is currently running on the device appears next to the System image file is text. The name of the hardware product appears on the line after the name of the system image file.

  The following example shows the output of the show version command on a device that is running Cisco IOS XR Software Release 6.5.2:

  RP/0/RSP0/CPU0:ASR9001#show version
  Tue May 14 01:32:32.751 EST
  
  Cisco IOS XR Software, Version 6.5.2[Default]
  Copyright (c) 2019 by Cisco Systems, Inc.
  
  ROM: System Bootstrap, Version 2.04(20140227:092320) [ASR9K ROMMON],  
  
  ASR9001 uptime is 6 hours, 17 minutes
  System image file is "bootflash:disk0/asr9k-os-mbi-5.3.4.sp4-1.0.0/0x100000/mbiasr9k-rp.vm"
  
  cisco ASR9K Series (P4040) processor with 8388608K bytes of memory.
  P4040 processor at 1500MHz, Revision 2.0
  ASR-9001 Chassis
  
  2 Management Ethernet
  8 TenGigE
  20 GigabitEthernet
  8 DWDM controller(s)
  8 WANPHY controller(s)
  44 GigabitEthernet/IEEE 802.3 interface(s)
  219k bytes of non-volatile configuration memory.
  2880M bytes of hard disk.
  3932144k bytes of disk0: (Sector size 512 bytes).
  
  Configuration register on node 0/RSP0/CPU0 is 0x2102 

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  No other Cisco products are currently known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect devices running Cisco IOS Software, Cisco IOS XE Software, or Cisco NX-OS Software.

Details

• EVPN is a next-generation solution that provides Ethernet multipoint services over MPLS networks. In EVPN, customers' MAC addresses are used as routable addresses. PE devices participating in an EVI use Multiprotocol BGP (MP-BGP) as a route learning and distribution mechanism.

  The vulnerability is due to a logic error that occurs when the affected software processes specific MP-BGP EVPN update messages. An attacker that controls multiple Customer Edge (CE) devices could exploit this vulnerability by injecting malicious traffic patterns into the EVPN network. An exploit could cause the Provider Edge (PE) device to advertise specific MP-BGP EVPN update messages that could result in a crash of the l2vpn_mgr process on PE device members of the same EVI.

Indicators of Compromise

• Exploitation of this vulnerability could cause the affected device to repeatedly generate an error message similar to the following:

  RP/0/RP0/CPU0:May 14 15:41:03.241 IST: syslog_dev[117]: l2vpn_mgr[1265] PID-8642:
  l2vpn/evpn/include/evpn_label_db_defs.h: 412 FALSE -- assertion failed

  Customers are advised to contact their support organization to review the error message and determine whether the device has been affected by exploitation of this vulnerability.

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 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.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.

  Fixed Releases

  The following table lists major software release trains of Cisco IOS XR Software, indicates whether a release train is affected by the vulnerabilities described in this advisory, and the first minor release that includes the fix for these vulnerabilities, if applicable. Customers should migrate to an appropriate release as indicated in the following table:

  Software Train	First Fixed Release	Recommended Release
  4.3	Not vulnerable	Not vulnerable
  5.0	Not vulnerable	Not vulnerable
  5.1	Not vulnerable	Not vulnerable
  5.2	Not vulnerable	Not vulnerable
  5.3	Not vulnerable	Not vulnerable
  6.0	Not vulnerable	Not vulnerable
  6.1	6.5.3	6.5.3
  6.2	6.5.3	6.5.3
  6.3	6.3.3	6.3.3
  6.4	6.4.2	6.4.2
  6.5	6.5.2	6.5.3
  6.6	6.6.1	6.6.12

  Cisco has also released a software maintenance upgrade (SMU) for Cisco Aggregation Services Router (ASR) 9000 Series that addresses this vulnerability.

  IOS XR Release	SMU ID	ASR 9000 SMU Name
  6.2.3	AA15558	asr9k-px-6.2.3.CSCvk35997

  The SMU/service pack can be downloaded from the Software Center on Cisco.com.

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.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190515-iosxr-evpn-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Added SMU information.	Fixed Software	Final	2019-July-10
  1.0	Initial public release.	-	Final	2019-May-15

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