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The Cisco ASA must be configured to filter inbound traffic on all external interfaces.


Overview

Finding ID Version Rule ID IA Controls Severity
V-239865 CASA-FW-000230 SV-239865r991797_rule Medium
Description
Unrestricted traffic to the trusted networks may contain malicious traffic that poses a threat to an enclave or to other connected networks. Additionally, unrestricted traffic may transit a network, which uses bandwidth and other resources. Firewall filters 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.
STIG Date
Cisco ASA Firewall Security Technical Implementation Guide 2024-06-06

Details

Check Text ( C-43098r665879_chk )
Review the ASA configuration to verify that it is filtering inbound traffic on all external interfaces.

access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.2 eq www
access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.2 eq https
access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.3 eq ftp
access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.3 eq ftp-data
access-list OUTSIDE_2_DMZ extended deny ip any any log



access-group OUTSIDE_2_DMZ in interface OUTSIDE

If the ASA is not configured to filter inbound traffic on all external interfaces, this is a finding.
Fix Text (F-43057r665880_fix)
Step 1: Configure the ACL to allow specific inbound traffic.

ASA(config)# access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.2 eq www
ASA(config)# access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.2 eq https
ASA(config)# access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.3 eq ftp
ASA(config)# access-list OUTSIDE_2_DMZ extended permit tcp any host 10.1.33.3 eq ftp-data
ASA(config)# access-list OUTSIDE_2_DMZ extended deny ip any any log

Step 2: Apply the ACL inbound to the external interface.

ASA(config)# access-group OUTSIDE_2_DMZ in interface OUTSIDE