The IAO/NSO will ensure IPv6 addresses with embedded IPv4-compatible IPv6 addresses are blocked on the ingress and egress filters, (0::/96).

From Perimeter Router Security Technical Implementation Guide Cisco

Part of Embedded IPv4-Compatible IPv6 ADDR are not blocked

SV-15411r1_rule The IAO/NSO will ensure IPv6 addresses with embedded IPv4-compatible IPv6 addresses are blocked on the ingress and egress filters, (0::/96).

Vulnerability discussion

The IPv6 transition mechanisms include a technique for hosts and routers to dynamically tunnel IPv6 packets over IPv4 routing infrastructure. IPv6 nodes that use this technique are assigned special IPv6 unicast addresses that carry a global IPv4 address in the low-order 32 bits. IPv4-compatible IPv6 addresses should never appear as a source or destination address. These addresses begin with 0000 and have ‘0000’ in the 16 bit field preceding the IPv4 address. RFC 4291 deprecated the IPv4-compatible addresses.

Check content

Base Procedure: Review the premise router configuration to ensure filters are in place to restrict the IP addresses explicitly, or inexplicitly. Verify that ingress and egress ACLs for IPv6 have been defined to deny the embedded IPv4-compatible IPv6 addresses and log all violations.

Fix text

The administrator will configure the router ACLs to restrict IP addresses that contain any embedded IPv4-compatible IPv6 addresses.

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