Summary

• A vulnerability in the IPv6 subsystem of Cisco IOS XR Software Release 5.3.4 for the Cisco Aggregation Services Router (ASR) 9000 Series could allow an unauthenticated, remote attacker to trigger a reload of one or more Trident-based line cards, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to incorrect handling of IPv6 packets with a fragment header extension. An attacker could exploit this vulnerability by sending IPv6 packets designed to trigger the issue either to or through the Trident-based line card. A successful exploit could allow the attacker to trigger a reload of Trident-based line cards, resulting in a DoS during the period of time the line card takes to restart.
  
  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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180131-ipv6

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Aggregation Services Router (ASR) 9000 Series when the following conditions are met:
  

  • The router is running Cisco IOS XR Software Release 5.3.4.
  • The router has installed Trident-based line cards that have IPv6 configured.

  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, 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 5.3.4:
  

  RP/0/RSP0/CPU0:ASR9001#show version
  Wed Jan 24 01:32:32.751 EST
  
  Cisco IOS XR Software, Version 5.3.4[Default]
  Copyright (c) 2017 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
  

  
  
  Determining if the Device Has a Trident-based Line Card
  
  The first generation of the Cisco ASR 9000 Series Ethernet line cards are often referred to as Trident-based (or Ethernet) line cards. The term comes from the Network Processors (NPs) that are used on these line cards. The following is a complete list of affected Trident-based line cards. Line cards not listed are not affected by this vulnerability:
  

  • A9K-40GE-L
  • A9K-40GE-B
  • A9K-40GE-E
  • A9K-4T-L
  • A9K-4T-B
  • A9K-4T-E
  • A9K-8T/4-L
  • A9K-8T/4-B
  • A9K-8T/4-E
  • A9K-2T20GE-L
  • A9K-2T20GE-B
  • A9K-2T20GE-E
  • A9K-8T-L
  • A9K-8T-B
  • A9K-8T-E
  • A9K-16/8T-B

  To determine whether the line card installed in the ASR 9000 Series Router is Trident-based, the administrator can use the show diag | include PID: command. Affected devices will include the product ID (PID) for at least one of the Trident-based line cards listed previously. The following example shows a device on which an A9K-8T-L card is active:
  

  RP/0/RSP0/CPU0:ASR9006-B#show diag | include PID:
  Tue Jan 26 00:07:09.406 EST
    PID:   A9K-RSP440-SE
    PID:   A9K-RSP440-SE
    PID:   A9K-8X100GE-SE
    PID:   A9K-8T-L
    PID:   A9K-36X10GE-SE
    PID:   A9K-MOD160-TR
    PID:   A9K-MPA-8X10GE 
    PID:   A9K-MPA-8X10GE 
  RP/0/RSP0/CPU0:ASR9006-B#

  For more information on Trident-based line cards, consult the ASR 9000 Series Line Card Types publication at the following URL: https://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/116726-qanda-product-00.html
  
  Determining if the Device Is Configured for IPv6
  
  Administrators can use the show ipv6 interface brief command to determine if an interface is enabled for IPv6 traffic processing. The following example shows an interface configured for IPv6 processing:
  

  RP/0/RP0/CPU0:router# show ipv6 interface brief
  GigabitEthernet0/2/0/0 [Up/Up]
  fe80::212:daff:fe62:c150
  202::1
  .
  .
  .

  
  The show ipv6 interface brief command will produce an error message if the running version of Cisco IOS XR Software does not support IPv6. The output will not show any interfaces with IPv6 addresses if IPv6 is disabled.
  
  An interface may be configured for IPv6 processing but may not appear on the output of the show ipv6 interface brief command if the interface is part of a bundle or a virtual routing and forwarding (VRF) instance. The show ipv6 vrf all interface command can be used to determine whether any interface has been configured in this way. The following is the output of the show ipv6 vrf all interface command showing an interface configured for IPv6 processing as part of a bundle and assigned to a VRF instance:
  

  RP/0/RP0/CPU0:Router#show ipv6 vrf all interface 
  .
  .
  .
  Bundle-Ether4.765 is Up, ipv6 protocol is Up, Vrfid is FDA (0x60000001)
    IPv6 is enabled, link-local address is fe80::21d:a2ff:aabb:ccdd
    Global unicast address(es):
      2001:db8:1:1::1, subnet is 2001:db8:1:1::/64 
    Joined group address(es): ff02::1:ff00:0 ff02::1:aabb:ccdd ff02::2
        ff02::1
    MTU is 1518 (1500 is available to IPv6)
    ICMP redirects are disabled
    ICMP unreachables are enabled
    ND DAD is enabled, number of DAD attempts 1
    ND reachable time is 0 milliseconds
    ND advertised retransmit interval is 0 milliseconds
    Hosts use stateless autoconfig for addresses.
    Outgoing access list is not set
    Inbound  access list is not set
    Table Id is 0xe0800001
  

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.
  
  Cisco Aggregation Services Router (ASR) 9000 Series that do not contain any Trident-based line cards, are not running Cisco IOS XR Software Release 5.3.4, or are not enabled for IPv6 are not affected.
  
  No other devices running Cisco IOS XR Software are affected.
  

Indicators of Compromise

• Exploitation of this vulnerability could cause the Trident-based line card to reload and generate error messages similar to the following:
  

  LC/0/6/CPU0:pfm_node_lc[285]: %PLATFORM-DIAGS-0-LC_NP_LOOPBACK_FAILED_RX_PATH : Set|online_diag_lc[163925]|Line card NPU loopback Test(0x2000006)|link failure mask is 0x20. 
  LC/0/6/CPU0:prm_server_tr[296]: %PLATFORM-NP-0-INIT_ERR : *** Error 0xA0003F03 : prm_np_fast_reset : Channel 5 Config Start Fast Reset failed, line card will be reloaded  
  LC/0/6/CPU0:prm_server_tr[296]: %PLATFORM-NP-4-FAULT : Line card needs to be reloaded, a reboot is being requested
  
  LC/0/5/CPU0:prm_server_tr[296]: %PLATFORM-NP-0-INIT_ERR : *** Error 0xA0003F03 : prm_np_fast_reset : Channel 5 Config Start Fast Reset failed, line card will be reloaded  
  LC/0/5/CPU0:prm_server_tr[296]: %PLATFORM-NP-4-FAULT : Line card needs to be reloaded, a reboot is being requested   
  LC/0/5/CPU0:syslog_dev[88]: prm_server_tr[296] PID-163922: reboot internal start: cause code 27 cause Fast Reset of the NP failed, LC reboot needed to recover the NP

  For a final confirmation on whether these message do indeed indicate exploitation of this issue, please contact your support organization.

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

  A software maintenance upgrade (SMU) has been made available that addresses this vulnerability. The fix has also been incorporated into service pack 7 for Cisco IOS XR Software Release 5.3.4.
  
  

  IOS XR Release	SMU ID	SMU/Service Pack Name
  5.3.4	AA13804	asr9k-px-5.3.4.CSCvg46800.tar
  5.3.4	AA13870	asr9k-px.5.3.4.sp7.tar

  
  The SMU/service pack can be downloaded from the Software Center on Cisco.com by navigating to the IOS XR Software Maintenance Upgrades (SMU)-5.3.4 or IOS XR Service Packs-5.3.4 respectively.

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 the resolution of a Cisco TAC support case.

URL

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180131-ipv6

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2018-January-31

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