Many WAFs rely partially on pattern matching and signatures. Attackers may evade simplistic detection using alternate syntax, encoding techniques, comments, or logically equivalent operators. Effective protection combines secure coding practices, parameterized queries, positive validation, and layered defenses rather than depending solely on signature detection.

According to CEH v13 Network Scanning Techniques, a FIN scan is a stealth scanning method that sends TCP packets with only the FIN flag set. Its behavior relies on RFC 793, which specifies that closed ports must respond with a TCP RST, while open ports should silently drop the packet.
However, modern firewalls, IDS/IPS systems, and hardened TCP/IP stacks often filter or silently drop FIN packets regardless of port state. Therefore, when a FIN scan results in no response from a large number of ports, it does not conclusively indicate that the ports are open. Instead, CEH v13 stresses that this behavior commonly points to packet filtering by firewalls or security controls.
Option A is incorrect because a lack of response does not definitively mean ports are closed. Option B is an overreaction; stealth scan anomalies alone do not indicate a breach. Option C is unlikely because congestion would impact multiple protocols, not selectively suppress FIN responses.
CEH v13 recommends that when FIN scans produce ambiguous results, analysts should correlate findings using additional scan types (such as SYN scans) and investigate firewall rules and filtering behavior. Thus, option D is the most accurate interpretation and aligns with CEH guidance.

In CEH v13 Module 01: Information Security Controls, the Remote Access Policy is defined as the guideline that governs:
Which remote access methods (VPNs, modems, RDP, etc.) are permitted.
Requirements for authentication and encryption.
Who is authorized to use them and under what conditions.
In This Case:
The use of a dial-out modem is considered a remote access method, especially if it bypasses the corporate firewall.
The analyst needs to check whether such remote access is permitted, and under what security controls.
Reference:
Module 01 - Policies and Governance: Remote Access Policy
CEH eBook: Policy Enforcement and Exception Auditing

Types of Vulnerability Assessment - External Assessment External assessment examines the network from a hacker's point of view to identify exploits and vulnerabilities accessible to the outside world. These types of assessments use external devices such as firewalls, routers, and servers. An external assessment estimates the threat of network security attacks from outside the organization. It determines the level of security of the external network and firewall. (P.527/511) External assessment examines the network from a hacker's point of view to identify exploits and vulnerabilities accessible to the outside world. These types of assessments use external devices such as firewalls, routers, and servers. An external assessment estimates the threat of network security attacks from outside the organization. It determines the level of security of the external network and firewall.
The following are some of the possible steps in performing an external assessment:
o Determine a set of rules for firewall and router configurations for the external network o Check whether the external server devices and network devices are mapped o Identify open ports and related services on the external network o Examine the patch levels on the server and external network devices o Review detection systems such as IDS, firewalls, and application-layer protection systems o Get information on DNS zones o Scan the external network through a variety of proprietary tools available on the Internet o Examine Web applications such as e-commerce and shopping cart software for vulnerabilities