Details

If outbound communications traffic is not filtered, hostile activity intended to harm other networks or packets from networks destined to unauthorized networks may not be detected and prevented.

Access control policies and access control lists implemented on devices, such as firewalls, that control the flow of network traffic ensure the flow of traffic is only allowed from authorized sources to authorized destinations. Networks with different levels of trust (e.g., the Internet) must be kept separated.

This requirement addresses the binding of the egress filter to the interface/zone rather than the content of the egress filter.

Solution

Step 1: Configure the egress ACL similar to the example below.

ASA(config)# access-list INSIDE_2_OUT extended permit tcp any any eq https
ASA(config)# access-list INSIDE_2_OUT extended permit tcp any any eq http
ASA(config)# access-list INSIDE_2_OUT extended permit tcp any any eq domain
ASA(config)# access-list INSIDE_2_OUT extended permit tcp any any eq ftp
ASA(config)# access-list INSIDE_2_OUT extended permit tcp any any eq ftp-data
ASA(config)# access-list INSIDE_2_OUT extended permit tcp any host 10.1.22.3 eq ssh
ASA(config)# access-list INSIDE_2_OUT extended deny ip any any log

Step 2: Apply the ACL inbound on the internal interfaces as shown in the example below.

ASA(config)# access-group INSIDE_2_OUT in interface INSIDE
ASA(config)# end

Supportive Information

The following resource is also helpful.

• https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_ASA_STIG.zip

This security hardening control applies to the following category of controls within NIST 800-53: System and Communications Protection.This control applies to the following type of system Cisco.

References

• 800-53|SC-7(11)
• CAT|II
• CCI|CCI-002403
• Rule-ID|SV-239866r665884_rule
• STIG-ID|CASA-FW-000240
• Vuln-ID|V-239866

Source

• Tenable.com/audits