STIGQter: STIG Summary: Cisco IOS XE Router RTR Security Technical Implementation Guide Version: 2 Release: 2 Benchmark Date: 23 Apr 2021:

The Cisco multicast Rendezvous Point (RP) router must be configured to limit the multicast forwarding cache so that its resources are not saturated by managing an overwhelming number of Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP) source-active entries.

DISA Rule

SV-216720r531086_rule

Vulnerability Number

V-216720

Group Title

SRG-NET-000362-RTR-000120

Rule Version

CISC-RT-000820

Severity

CAT III

CCI(s)

• CCI-002385 - The information system protects against or limits the effects of organization-defined types of denial of service attacks by employing organization-defined security safeguards.

Weight

10

Fix Recommendation

The risk associated with this requirement can be fully mitigated by configuring the router to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers.

Step 1: Configure the router to filter PIM register messages received from a multicast DR for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources 10.1.2.6 and 10.1.2.7.

R2(config)#ip access-list extended PIM_REGISTER_FILTER
R2(config-ext-nacl)#deny ip any 239.5.0.0 0.0.255.255
R2(config-ext-nacl)#permit ip host 10.1.2.6 any
R2(config-ext-nacl)#permit ip host 10.1.2.7 any
R2(config-ext-nacl)#deny ip any any
R2(config-ext-nacl)#exit
R2(config)#ip pim accept-register list PIM_REGISTER_FILTER
R2(config)#end

Step 2: Configure the RP to rate limit the number of multicast register messages.

R2(config)#ip pim register-rate-limit nn

Step 3: Configure the receive path or interface ACLs to only accept MSDP packets from known MSDP peers.

R8(config)#ip access-list extended EXTERNAL_ACL_INBOUND
R8(config-ext-nacl)#permit tcp any any established
R8(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq 639
R8(config-ext-nacl)#deny tcp any host x.1.28.8 eq 639
R8(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq bgp
R8(config-ext-nacl)#permit tcp host x.1.28.2 eq bgp host x.1.28.8
R8(config-ext-nacl)#permit pim host x.1.28.2 host x.1.28.8
…
…
…
R8(config-ext-nacl)#deny ip any any

Check Contents

The Cisco router does not have a mechanism to limit the multicast forwarding cache. However, the risk associated with this requirement can be fully mitigated by configuring the router to:

1. Filter PIM register messages.
2. Rate limiting the number of PIM register messages.
3. Accept MSDP packets only from known MSDP peers.

Step 1: Verify that the RP router is configured to filter PIM register messages for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources 10.1.2.6 and 10.1.2.7.

ip pim rp-address 10.1.12.3
ip pim accept-register list PIM_REGISTER_FILTER
…
…
…
ip access-list extended PIM_REGISTER_FILTER
deny ip any 239.5.0.0 0.0.255.255
permit ip host 10.1.2.6 any
permit ip host 10.1.2.7 any
deny ip any any

Step 2: Verify that the router is configured to rate limiting the number of PIM register messages as shown in the example below.

ip pim rp-address 10.2.2.2
ip pim register-rate-limit nn

Step 3: Review the router configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers as shown in the example below.

Step 3a: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example.

interface GigabitEthernet1/1
ip address x.1.28.8 255.255.255.0
ip access-group EXTERNAL_ACL_INBOUND in
ip pim sparse-mode

Step 3b: Verify that the ACL restricts MSDP peering to only known sources.

ip access-list extended EXTERNAL_ACL_INBOUND
permit tcp any any established
permit tcp host x.1.28.2 host x.1.28.8 eq 639
deny tcp any host x.1.28.8 eq 639 log
permit tcp host x.1.28.2 host 10.1.28.8 eq bgp
permit tcp host x.1.28.2 eq bgp host x.1.28.8
permit pim host x.1.28.2 pim host x.1.28.8
…
…
…
deny ip any any log

Note: MSDP connections is via TCP port 639

If the RP router is not configured to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers, this is a finding.

Vulnerability Number

V-216720

Documentable

False

Rule Version

CISC-RT-000820

Severity Override Guidance

The Cisco router does not have a mechanism to limit the multicast forwarding cache. However, the risk associated with this requirement can be fully mitigated by configuring the router to:

1. Filter PIM register messages.
2. Rate limiting the number of PIM register messages.
3. Accept MSDP packets only from known MSDP peers.

Step 1: Verify that the RP router is configured to filter PIM register messages for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources 10.1.2.6 and 10.1.2.7.

ip pim rp-address 10.1.12.3
ip pim accept-register list PIM_REGISTER_FILTER
…
…
…
ip access-list extended PIM_REGISTER_FILTER
deny ip any 239.5.0.0 0.0.255.255
permit ip host 10.1.2.6 any
permit ip host 10.1.2.7 any
deny ip any any

Step 2: Verify that the router is configured to rate limiting the number of PIM register messages as shown in the example below.

ip pim rp-address 10.2.2.2
ip pim register-rate-limit nn

Step 3: Review the router configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers as shown in the example below.

Step 3a: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example.

interface GigabitEthernet1/1
ip address x.1.28.8 255.255.255.0
ip access-group EXTERNAL_ACL_INBOUND in
ip pim sparse-mode

Step 3b: Verify that the ACL restricts MSDP peering to only known sources.

ip access-list extended EXTERNAL_ACL_INBOUND
permit tcp any any established
permit tcp host x.1.28.2 host x.1.28.8 eq 639
deny tcp any host x.1.28.8 eq 639 log
permit tcp host x.1.28.2 host 10.1.28.8 eq bgp
permit tcp host x.1.28.2 eq bgp host x.1.28.8
permit pim host x.1.28.2 pim host x.1.28.8
…
…
…
deny ip any any log

Note: MSDP connections is via TCP port 639

If the RP router is not configured to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers, this is a finding.

Check Content Reference

M

Target Key

4028

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