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The Cisco perimeter switch must be configured to drop IPv6 packets containing a Hop-by-Hop or Destination Option extension header with an undefined option type.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-237778 | CISC-RT-000398 | SV-237778r648823_rule | Medium |
| Description |
|---|
| The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many implementations do not always drop packets with headers that it cannot recognize, and hence could cause a Denial-of-Service on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. |
| STIG | Date |
|---|---|
| Cisco IOS-XE Switch RTR Security Technical Implementation Guide | 2021-03-26 |
Details
| Check Text ( C-40988r648820_chk ) |
|---|
| This requirement is not applicable for the DODIN Backbone. Review the switch configuration and determine if filters are bound to the applicable interfaces to drop all inbound IPv6 packets containing an undefined option type value regardless of whether they appear in a Hop-by-Hop or Destination Option header. Undefined values are 0x02, 0x03, 0x06, 0x9 – 0xE, 0x10 – 0x22, 0x24, 0x25, 0x27 – 0x2F, and 0x31 – 0xFF. Step 1: Verify that an inbound IPv6 ACL has been configured on the external interface. interface gigabitethernet1/0 ipv6 address 2001::1:0:22/64 ipv6 traffic-filter FILTER_IPV6 in Step 2: Verify that the ACL drops IPv6 packets containing a Hop-by-Hop or Destination Option extension header with an undefined option type as shown in the example below. ipv6 access-list FILTER_IPV6 deny any any dest-option-type 2 deny any any dest-option-type 3 deny any any dest-option-type 6 deny any any dest-option-type 9 deny any any dest-option-type 10 deny any any dest-option-type 11 deny any any dest-option-type 12 deny any any dest-option-type 13 deny any any dest-option-type 14 deny any any dest-option-type 16 … deny any any dest-option-type 34 deny any any dest-option-type 36 deny any any dest-option-type 37 deny any any dest-option-type 39 … deny any any dest-option-type 47 deny any any dest-option-type 49 … deny any any dest-option-type 255 permit … … … … deny ipv6 any any log Note: Because hop-by-hop and destination options have the same exact header format, they can be combined under the dest-option-type keyword. Since Hop-by-Hop and Destination Option headers have non-overlapping types, you can use dest-option-type to match either. If the switch is not configured to drop IPv6 packets containing a Hop-by-Hop or Destination Option extension header with an undefined option type, this is a finding. |
| Fix Text (F-40947r648821_fix) |
|---|
| Configure the switch to drop all inbound IPv6 packets containing an undefined option type value regardless of whether they appear in a Hop-by-Hop or Destination Option header as shown in the example below. SW1(config)#ipv6 access-list FILTER_IPV6 SW1(config-ipv6-acl)#deny any any dest-option-type 2 SW1(config-ipv6-acl)#deny any any dest-option-type 3 SW1(config-ipv6-acl)#deny any any dest-option-type 6 SW1(config-ipv6-acl)#deny any any dest-option-type 9 SW1(config-ipv6-acl)#deny any any dest-option-type 10 SW1(config-ipv6-acl)#deny any any dest-option-type 11 SW1(config-ipv6-acl)#deny any any dest-option-type 12 SW1(config-ipv6-acl)#deny any any dest-option-type 13 SW1(config-ipv6-acl)#deny any any dest-option-type 14 SW1(config-ipv6-acl)#deny any any dest-option-type 16 … SW1(config-ipv6-acl)#deny any any dest-option-type 34 SW1(config-ipv6-acl)#deny any any dest-option-type 36 SW1(config-ipv6-acl)#deny any any dest-option-type 37 SW1(config-ipv6-acl)#deny any any dest-option-type 39 … SW1(config-ipv6-acl)#deny any any dest-option-type 47 SW1(config-ipv6-acl)#deny any any dest-option-type 49 … SW1(config-ipv6-acl)#deny any any dest-option-type 255 SW1(config-ipv6-acl)#permit … … … … SW1(config-ipv6-acl)#deny ipv6 any any log SW1(config-ipv6-acl)#exit SW1(config)#int g1/0 SW1(config-if)#ipv6 traffic-filter FILTER_IPV6 |