Attackers take advantage of the fact that network devices may become less securely configured over time as users demand exceptions for specific and temporary business needs, as the exceptions are deployed, and as those exceptions are not undone when the business need is no longer applicable. Making matters worse, in some cases, the security risk of the exception is neither properly analyzed nor measured against the associated business need and can change over time. Attackers search for electronic holes in firewalls, routers, and switches and use those to penetrate defenses. Attackers have exploited flaws in these network devices to gain access to target networks, redirect traffic on a network (to a malicious system masquerading as a trusted system), and intercept and alter information while in transmission. Through such actions, the attacker gains access to sensitive data, alters important information, or even uses one compromised machine to pose as another trusted system on the network.
1. Quick wins: Compare firewall, router, and switch configuration against standard secure configurations defined for each type of network device in use in the organization. The security configuration of such devices should be documented, reviewed, and approved by an organization change control board. Any deviations from the standard configuration or updates to the standard configuration should be documented and approved in a change control system.
2. Quick wins: At network interconnection points-such as Internet gateways, inter-organization connections, and internal network segments with different security controls--implement ingress and egress filtering to allow only those ports and protocols with an explicit and documented business need. All other ports and protocols should be blocked with default-deny rules by firewalls, network-based IPS, and/or routers.
3. Configuration/Hygiene: All new configuration rules beyond a baseline-hardened configuration that allow traffic to flow through network security devices, such as firewalls and network-based IPS, should be documented and recorded in a configuration management system, with a specific business reason for each change, a specific individual's name responsible for that business need, and an expected duration of the need.
4. Configuration/Hygiene: Network filtering technologies employed between networks with different security levels (firewalls, network-based IPS tools, and routers with access controls lists) should be deployed with capabilities to filter Internet Protocol version 6 (IPv6) traffic. However, if IPv6 is not currently being used it should be disabled. Since many operating systems today ship with IPv6 support activated, filtering technologies need to take it into account.
5. Configuration/Hygiene: Manage network devices using two-factor authentication and encrypted sessions.
6. Configuration/Hygiene: Install the latest stable version of any security-related updates within 30 days of the update being released from the device vendor.
7. Advanced: Manage the network infrastructure across network connections that are separated from the business use of that network, relying on separate VLANs or, preferably, on entirely different physical connectivity for management sessions for network devices.
AC-4 (7, 10, 11, 16), CM-1, CM-2 (1), CM-3 (2), CM-5 (1, 2, 5), CM-6 (4), CM-7 (1, 3), IA-2 (1, 6), IA-5, IA-8, RA-5, SC-7 (2, 4, 5, 6, 8, 11, 13, 14, 18), SC-9
Milestone 7: Baseline Management
Configuration and Change Management
Some organizations use commercial tools that evaluate the rule set of network filtering devices to determine whether they are consistent or in conflict, providing an automated sanity check of network filters and search for errors in rule sets or access controls lists (ACLs) that may allow unintended services through the device. Such tools should be run each time significant changes are made to firewall rule sets, router ACLs, or other filtering technologies.
The system must be capable of identifying any changes to network devices, including routers, switches, firewalls, and IDS and IPS systems. These changes include any modifications to key files, services, ports, configuration files, or any software installed on the device. Modifications include deletions, changes, or additions of new software to any part of the device configuration. The configuration of each system must be checked against the official master image database to verify any changes to secure configurations that would impact security. This includes both operating system and configuration files. Any of these changes to a device must be detected within 24 hours and notification performed by alerting or sending e-mail notification to a list of enterprise personnel. If possible, devices must prevent changes to the system and send an alert indicating the change was not successful. Every 24 hours after that point, the system must alert or send e-mail about the status of the system until it is investigated and/or remediated.
To evaluate the implementation of Control 10 on a periodic basis, an evaluation team must make a change to each type of network device plugged into the network. At a minimum, routers, switches, and firewalls need to be tested. If they exist, IPS, IDS, and other network devices must be included. Backups must be made prior to making any changes to critical network devices. It is critical that changes not impact or weaken the security of the device. Acceptable changes include but are not limited to making a comment or adding a duplicate entry in the configuration. The change must be performed twice for each critical device. The evaluation team must then verify that the systems generate an alert or e-mail notice regarding the changes to the device within 24 hours. It is important that the evaluation team verify that all unauthorized changes have been detected and have resulted in an alert or e-mail notification. The evaluation team must verify that the system provides details of the location of each device, including information about the asset owner. While the 24-hour timeframe represents the current metric to help organizations improve their state of security, in the future organizations should strive for even more rapid alerting and isolation, with notification about unauthorized configuration changes in network devices sent within two minutes.
If appropriate, an additional test must be performed on a daily basis to ensure that other protocols such as IPv6 are properly being filtered.
Organizations will find that by diagramming the entities necessary to fully meet the goals defined in this control, it will be easier to identify how to implement them, test the controls, and identify where potential failures in the system might occur.
A control system is a device or set of devices used to manage, command, direct, or regulate the behavior of other devices or systems. In this case we are examining the network devices, test lab network devices, configuration systems, and configuration management devices. The following list of the steps in the diagram above shows how the entities work together to meet the business goal defined in this control. The list also delineates each of the process steps in order to help identify potential failure points in the overall control.
Step 1: Hardened device configurations applied to production devices
Step 2: Hardened device configuration stored in a secure configuration management system
Step 3: Management network system validates configurations on production network devices
Step 4: Patch management system applies tested software updates to production network devices
Step 5:Two-factor authentication system required for administrative access to production devices
Step 6: Proxy/firewall/network monitoring systems analyze all connections to production network devices.