# Firewall Best Practices for Securing Smart Healthcare Environment: A Review
## 5 Firewall Vulnerabilities  
The classification of firewall vulnerabilities may help to find (quicker) any potential issue exposing a network system to security concerns throughout the use of that firewall policy. Common issues generally include wrong configurations, design errors, or misleading firewall configurations and settings; thus, disclosure of poor and unsatisfactory security policies [65]. Even worse, a misconfigured firewall may leave the system, which is supposed to be protected, exploited from the outside. Vulnerabilities, such as validation or design errors, are generally associated with IP and port filtering practices. When an error occurs, the probability of a malicious event or an attack (e.g., DDoS issue) increases accordingly. Moreover, a vulnerability belonging to the first layers of the OSI model (e.g., Layer 3) is still present in other layers touched by that application. In other words, layers are correlated with each other, and vulnerabilities cumulate throughout the layers. Vulnerabilities follow the fault classification scheme [66; 67]. Spurious, misplaced, missing, and incorrect entities are erroring whose corrections may require an insertion, a change, or removal of an entity from the original source code to fix that vulnerability. Some common vulnerabilities affecting both hardware and software firewalls are troubles in rejecting policy for illegitimate network traffic, ignoring rules for malicious threats, lack of security rules for domestic network traffic, then causing insider attacks. Vulnerabilities typically affecting only software firewalls are any malicious action aiming to bypass the firewall by exploiting it at the application layer (application control, masquerade, prevent loading, firewall uninstall, etc.), or any attempt to move the application of the firewall at a lower level, such as the network layer [68].  
Firewall vulnerabilities can be resumed into two big categories: (a) vulnerabilities related to design constraints and limitations; (b) vulnerabilities related to misconfigured firewall policy and rules. While in the second category, best practices can potentially fix the vulnerability assumed in that system (soft vulnerability), vulnerabilities of the first category are typically due to design/topology issues, then best practices can only be applied at the source (hard vulnerability), by providing, for example, a new design of the firewall [68]. Firewall engineers should always avoid the first category of vulnerabilities that happen after the testing stage of the product cycle has been validated. As a result, software firewalls disclosing hard vulnerabilities in production environments will no longer be used, and then uninstalled, and firewalls that are more effective will be considered. Table 2 provides the most frequent and common firewall vulnerabilities in the function of the firewall type(s) by cause, effect, and fix remedy of the issue found. For example, an issue, such as the validation error, occurring when a program is running in an environment regardless of the correctness of the data introduced in that environment (cause), is strictly related to a DDoS issue (effect). Likewise, firewall design errors (cause) lead to issues in the execution of codes (effect) [69].  
The role of firewalls in smart healthcare as a technical countermeasure has been progressively recognized in the security life cycle as an important tool to achieve security goals [70]. This work is a capstone for security and provides a clear categorization of firewall types and practices, also treating security for cloud environments.  
Regardless of the firewall type and the technology used, a fully effective firewall would always protect against internal and external security weaknesses and provide the right trade-off between security and performance [42]. Conversely, the correct use of firewalls within a system can be a powerful and effective resource in terms of security protection.