This article explains why some traffic is allowed through a route based VPN, even when the source or destination IP (or network) is not specified in proxy-identity .

Two devices are directly connected, with VPN configuration as follows:

Device 1:

root@srx# show security ipsec
<...Output Snipped...>
        vpn vpn1 {
            bind-interface st0.0;
            ike {
                gateway ikeg;
                proxy-identity {
                    local 192.168.1.0/24;
                    remote 192.168.2.0/24;
                    service any;
                }
                ipsec-policy ipsecp;
            }
            establish-tunnels immediately;
        }

Device 2:

root@srx# show security ipsec
<...Output Snipped...>
        vpn vpn1 {
            bind-interface st0.0;
            ike {
                gateway ikeg;
                proxy-identity {
                    local 192.168.2.0/24;
                    remote 192.168.1.0/24;
                    service any;
                }
                ipsec-policy ipsecp;
            }
            establish-tunnels immediately;
        }

Loopback is configured on these devices and given routes:

Device-1:

root@240-POE-1# show interfaces lo0
unit 0 {
    family inet {
        address 192.168.4.1/32;
    }
}

[edit]
root@240-POE-1# show routing-options
static {
    route 192.168.3.1/32 next-hop st0.0;
}

Device-2:

xroot@240-POE-2# show interfaces lo0
unit 0 {
    family inet {
        address 192.168.3.1/32;
    }
}

[edit]
root@240-POE-2# show routing-options
static {
    route 192.168.4.1/32 next-hop st0.0;
}

root@srx# run show security flow session protocol icmp
Session ID: 55490, Policy name: default-policy-00/2, Timeout: 2, Valid
  In: 192.168.4.1/0 --> 192.168.3.1/23053;icmp, If: st0.0, Pkts: 1, Bytes: 84 >>>>>Coming through st0 i.e. VPN
  Out: 192.168.3.1/23053 --> 192.168.4.1/0;icmp, If: .local..0, Pkts: 1, Bytes: 84

Session ID: 55492, Policy name: default-policy-00/2, Timeout: 4, Valid
  In: 192.168.4.1/1 --> 192.168.3.1/23053;icmp, If: st0.0, Pkts: 1, Bytes: 84
  Out: 192.168.3.1/23053 --> 192.168.4.1/1;icmp, If: .local..0, Pkts: 1, Bytes: 84

When proxy-identity is configured, it is only used during the negotiation of the VPN. After the negotiation completes, the PFE module does not detect these proxy-identities. Hence once the VPN comes up, any traffic can go into the VPN.

The solution is to use traffic-selectors (introduced in Junos OS 12.1X46) as described here:  Example: Configuring Traffic Selectors in a Route-Based VP .   Traffic-selectors push the negotiated networks to the packet forwarding engine (PFE) module, and thus flow will only allow traffic configured in traffic selectors .