The Juniper router must be configured to have Internet Control Message Protocol (ICMP) unreachable notifications disabled on all external interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-254034	JUEX-RT-000620	SV-254034r844135_rule		Medium

Description
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Host unreachable ICMP messages are commonly used by attackers for network mapping and diagnosis.

STIG	Date
Juniper EX Series Switches Router Security Technical Implementation Guide	2024-06-10

Details

Check Text ( C-57486r844133_chk )
Review the device configuration to determine if controls have been defined to ensure the router does not send ICMP unreachable notifications out to any external interfaces. [edit policy-options] prefix-list router-address-ipv4 { /32; /; } [edit firewall family inet] filter { term 1 { from { source-prefix-list { router-address-ipv4; } protocol icmp; icmp-type unreachable; } then { log; syslog; discard; } } term default { then { log; syslog; discard; } } } [edit interfaces] { unit { family inet { filter { output ; } address /; } } } Note: Some Juniper devices support both monolithic filters and filter lists. Filter lists separate each term, or set of terms, into a separate filter that is applied sequentially to an interface. If using filter lists, the keywords "input" or "output" change to "input-list" or "output-list". Verify the final list item is a deny-all filter. The deny-all filter is created once per family and can be reused across multiple lists. For example: input-list [ permit_mgt permit_routing_protocols default-deny ]; If ICMP unreachable notifications are enabled on any external interfaces, this is a finding.

Check Text ( C-57486r844133_chk )

Review the device configuration to determine if controls have been defined to ensure the router does not send ICMP unreachable notifications out to any external interfaces.

[edit policy-options]
prefix-list router-address-ipv4 {
/32;
/;
}
[edit firewall family inet]
filter {
term 1 {
from {
source-prefix-list {
router-address-ipv4;
}
protocol icmp;
icmp-type unreachable;
}
then {
log;
syslog;
discard;
}
}

term default {
then {
log;
syslog;
discard;
}
}
}

[edit interfaces]
{
unit {
family inet {
filter {
output ;
}
address /;
}
}
}

Note: Some Juniper devices support both monolithic filters and filter lists. Filter lists separate each term, or set of terms, into a separate filter that is applied sequentially to an interface. If using filter lists, the keywords "input" or "output" change to "input-list" or "output-list". Verify the final list item is a deny-all filter. The deny-all filter is created once per family and can be reused across multiple lists. For example:

input-list [ permit_mgt permit_routing_protocols default-deny ];

If ICMP unreachable notifications are enabled on any external interfaces, this is a finding.

Fix Text (F-57437r844134_fix)
Disable ICMP unreachable notifications on all external interfaces. set policy-options prefix-list router-addresses-ipv4 /32 set policy-options prefix-list router-addresses-ipv4 / set firewall family inet filter term 1 from source-prefix-list router-address-ipv4 set firewall family inet filter term 1 from protocol icmp set firewall family inet filter term 1 from icmp-type unreachable set firewall family inet filter term 1 then log set firewall family inet filter term 1 then syslog set firewall family inet filter term 1 then discard set firewall family inet filter term default then log set firewall family inet filter term default then syslog set firewall family inet filter term default then discard set interfaces unit family inet filter output set interfaces unit family inet address .

Fix Text (F-57437r844134_fix)

Disable ICMP unreachable notifications on all external interfaces.

set policy-options prefix-list router-addresses-ipv4 /32
set policy-options prefix-list router-addresses-ipv4 /

set firewall family inet filter term 1 from source-prefix-list router-address-ipv4
set firewall family inet filter term 1 from protocol icmp
set firewall family inet filter term 1 from icmp-type unreachable
set firewall family inet filter term 1 then log
set firewall family inet filter term 1 then syslog
set firewall family inet filter term 1 then discard

set firewall family inet filter term default then log
set firewall family inet filter term default then syslog
set firewall family inet filter term default then discard

set interfaces unit family inet filter output
set interfaces unit family inet address .