The administrator must ensure the perimeter router is configured to drop all inbound and outbound IPv6 packets containing the NSAP address option.

From Perimeter Router Security Technical Implementation Guide Juniper

Part of NSAP address option not filtered

SV-40439r1_rule The administrator must ensure the perimeter router is configured to drop all inbound and outbound IPv6 packets containing the NSAP address option.

Vulnerability discussion

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 can’t recognize and hence could cause a DoS on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, headers which may be valid but serve no intended use should not be allowed into or out of any network (S0-C2-opt-3). This option type from RFC 1888 (OSI NSAPs and IPv6) has been deprecated by RFC 4048.

Check content

Review the perimeter router or multi-layer switch configuration and determine if filters are bound to the applicable interfaces to drop all inbound and outbound IPv6 packets containing a Destination Option header with option type value of 0xC3 (NSAP address). The following example will block any inbound IPv6 packet containing a Destination Option header: interfaces fe-0/0/1 { unit 0 { family inet6 { filter { input IPV6-INGRESS-FILTER; } address 2001:1:0:146::4/64; } } } firewall { filter IPV6-INGRESS-FILTER { term DROP-DEST-OPT { from { next-header { dstops; } } then { syslog; discard; } } … … term default-action { then { syslog; discard; } } } } Note: Currently JUNOS has no method to filter option type within either Hop-by-Hop or Destination Option header. Hence, all packets with the Destination Option header must be dropped.

Fix text

Configure the perimeter router or multi-layer switch to drop all inbound and outbound IPv6 packets containing a Destination Option header with option type value of 0xC3 (NSAP address).

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