The VPN gateway peer at a remote site must receive all ingress traffic and forward all egress traffic via the IPSec tunnel or other provisoned WAN links connected to the central or remote site.

From IPSec VPN Gateway Security Technical Implementation Guide

Part of Remote VPN gateway leaks unprotected traffic into IP backbone.

Associated with IA controls: ECSC-1

SV-40995r1_rule The VPN gateway peer at a remote site must receive all ingress traffic and forward all egress traffic via the IPSec tunnel or other provisoned WAN links connected to the central or remote site.

Vulnerability discussion

A VPN gateway peer at the remote site provides connectivity to the central or other remote sites belonging to the enclave via an IPSec tunnel across an IP backbone network such as the NIPRNet. This creates an extension or Intranet for the enclave using IPSec tunnels in lieu of traditional or legacy WAN services (T carrier, ATM, frame relay, etc). Unless the remote site has the required enclave perimeter defense (firewall, IPS, deny by default, etc), it is imperative that all inbound and outbound traffic traverse only the IPSec tunnels or other provisioned WAN links connecting the remote site to other sites belonging to the enclave. In other words, no packets can leak out an external-facing interface as “native” IP traffic into an IP backbone (i.e. NIPRNet, Internet). In addition, the external interface must not receive any traffic that is not secured by an IPSec tunnel or other provisioned WAN links connected to the central or remote site. This not only ensures that inbound and outbound traffic does not bypass the enclave’s perimeter defense, but also eliminates any backdoor connection.

Check content

Review the remote VPN gateway interface configurations. All external-facing interfaces connected to an IP backbone network (i.e. NIPRNet) must have an IPSec crypto map bound to it or be the source of an IPSec-protected virtual tunnel interface. All inbound traffic must either map to a crypto map bound to a physical interface or be received via the virtual tunnel interface. Likewise, all outbound traffic must either map to a crypto map bound to a physical interface or be forwarded via the virtual tunnel interface. The remote VPN client can have WAN links connecting to other remote sites and the central sites. Traffic traversing these links does not need to be encrypted as they are part of the enclave’s private network.

Fix text

Configure the VPN gateway at the remote site to ensure it receives all ingress traffic and forward all egress traffic via the IPSec tunnel. All inbound and outbound traffic must be considered interesting traffic for the IPSec crypto maps bound to the external interfaces. If IPSec-protected virtual tunnel interfaces are configured, all traffic must flow through them or other provisioned WAN links connecting the remote site to other sites belonging to the enclave.

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