Cisco Aggregation Services Router 9000 Series IPv6 Fragment Header Denial of Service Vulnerability

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

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.

from Cisco Security Advisory http://ift.tt/2nmugYv