VMware NSX-T Tier 1 Gateway Firewall Security Technical Implementation Guide

Without establishing what type of event occurred, it would be difficult to establish, correlate, and investigate the events leading up to an outage or attack. Audit event content that may be necessary to satisfy this requirement includes, for example, time stamps, source and destination addresses, user/process identifiers, event descriptions, success/fail indications, filenames involved, and access control or flow control rules invoked. Associating event types with detected events in the network element logs provides a means of investigating an attack, recognizing resource utilization or capacity thresholds, or identifying an improperly configured network element.

It is critical that when the network element is at risk of failing to process traffic logs as required, it takes action to mitigate the failure, secure collected log data, and restrict access to authorized personnel. Methods of protection may include encryption or logical separation. In accordance with DOD policy, the traffic log must be sent to a central audit server. This does not apply to traffic logs generated on behalf of the device itself (management). Some devices store traffic logs separately from the system logs. Satisfies: SRG-NET-000089-FW-000019, SRG-NET-000098-FW-000021

DoS attacks can take multiple forms but have the common objective of overloading or blocking a network or host to deny or seriously degrade performance. If the network does not provide safeguards against DoS attacks, network resources will be unavailable to users. Installation of a firewall at key boundaries in the architecture mitigates the risk of DoS attacks. These attacks can be detected by matching observed communications traffic with patterns of known attacks and monitoring for anomalies in traffic volume/type. The firewall must include protection against DoS attacks that originate from inside the enclave that can affect either internal or external systems. These attacks may use legitimate or rogue endpoints from inside the enclave. These attacks can be simple "floods" of traffic to saturate circuits or devices, malware that consumes CPU and memory on a device or causes it to crash, or a configuration issue that disables or impairs the proper function of a device. For example, an accidental or deliberate misconfiguration of a routing table can misdirect traffic for multiple networks. Satisfies: SRG-NET-000192-FW-000029, SRG-NET-000193-FW-000030

To prevent malicious or accidental leakage of traffic, organizations must implement a deny-by-default security posture at the network perimeter. Such rulesets prevent many malicious exploits or accidental leakage by restricting the traffic to only known sources and only those ports, protocols, or services that are permitted and operationally necessary. This configuration which is in the Manager function of the NSX-T implementation also helps prevent the firewall instance from failing to a state that may cause unauthorized access to make changes to the firewall filtering functions. As a managed boundary interface, the firewall must block all inbound and outbound network traffic unless a filter is installed to explicitly allow it. The allow filters must comply with the Ports, Protocols, and Services Management (PPSM) Category Assurance List (CAL) and Vulnerability Assessment (VA). Satisfies: SRG-NET-000235-FW-000133, SRG-NET-000236-FW-000027

Without the ability to centrally manage the content captured in the traffic log entries, identification, troubleshooting, and correlation of suspicious behavior would be difficult and could lead to a delayed or incomplete analysis of an ongoing attack. The DoD requires centralized management of all network component audit record content. Network components requiring centralized traffic log management must have the ability to support centralized management. The content captured in traffic log entries must be managed from a central location (necessitating automation). Centralized management of traffic log records and logs provides for efficiency in maintenance and management of records, as well as the backup and archiving of those records. Ensure at least one syslog server is configured on the firewall. If the product inherently has the ability to store log records locally, the local log must also be secured. However, this requirement is not met since it calls for a use of a central audit server.

Not configuring a key boundary security protection device such as the firewall, against commonly known attacks is an immediate threat to the protected enclave because they are easily implemented by those with little skill. Directions for the attack are obtainable on the internet and in hacker groups. Without filtering enabled for these attacks, the firewall will allow these attacks beyond the protected boundary. Configure the perimeter and internal boundary firewall to guard against the three general methods of well-known DoS attacks: flooding attacks, protocol sweeping attacks, and unauthorized port scanning. Flood attacks occur when the host receives too much traffic to buffer and slows down or crashes. Popular flood attacks include ICMP flood and SYN flood. A TCP flood attack of SYN packets initiating connection requests can overwhelm the device until it can no longer process legitimate connection requests, resulting in denial of service. An ICMP flood can overload the device with so many echo requests (ping requests) that it expends all its resources responding and can no longer process valid network traffic, also resulting in denial of service. An attacker might use session table floods and SYN-ACK-ACK proxy floods to fill up the session table of a host. In an IP address sweep attack, an attacker sends ICMP echo requests (pings) to multiple destination addresses. If a target host replies, the reply reveals the target’s IP address to the attacker. In a TCP sweep attack, an attacker sends TCP SYN packets to the target device as part of the TCP handshake. If the device responds to those packets, the attacker gets an indication that a port in the target device is open, which makes the port vulnerable to attack. In a UDP sweep attack, an attacker sends UDP packets to the target device. If the device responds to those packets, the attacker gets an indication that a port in the target device is open, which makes the port vulnerable to attack. In a port scanning attack, an unauthorized application is used to scan the host devices for available services and open ports for subsequent use in an attack. This type of scanning can be used as a DoS attack when the probing packets are sent excessively.

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 and 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.

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