ISC Updated CISSP Exam Questions and Answers by emre

Adding a new rule to the application layer firewall is the most suited to quickly implement a control for an input validation and exception handling vulnerability on a critical web-based system. An input validation and exception handling vulnerability is a type of vulnerability that occurs when a web-based system does not properly check, filter, or sanitize the input data that is received from the users or other sources, or does not properly handle the errors or exceptions that are generated by the system. An input validation and exception handling vulnerability can lead to various attacks, such as:

• Injection attacks, such as SQL injection, command injection, or cross-site scripting (XSS), where the attacker inserts malicious code or commands into the input data that are executed by the system or the browser, resulting in data theft, data manipulation, or remote code execution.
• Buffer overflow attacks, where the attacker sends more input data than the system can handle, causing the system to overwrite the adjacent memory locations, resulting in data corruption, system crash, or arbitrary code execution.
• Denial-of-service (DoS) attacks, where the attacker sends malformed or invalid input data that cause the system to generate excessive errors or exceptions, resulting in system overload, resource exhaustion, or system failure.

An application layer firewall is a device or software that operates at the application layer of the OSI model and inspects the application layer payload or the content of the data packets. An application layer firewall can provide various functions, such as:

• Filtering the data packets based on the application layer protocols, such as HTTP, FTP, or SMTP, and the application layer attributes, such as URLs, cookies, or headers.
• Blocking or allowing the data packets based on the predefined rules or policies that specify the criteria for the application layer protocols and attributes.
• Logging and auditing the data packets for the application layer protocols and attributes.
• Modifying or transforming the data packets for the application layer protocols and attributes.

Adding a new rule to the application layer firewall is the most suited to quickly implement a control for an input validation and exception handling vulnerability on a critical web-based system, because it can prevent or reduce the impact of the attacks by filtering or blocking the malicious or invalid input data that exploit the vulnerability. For example, a new rule can be added to the application layer firewall to:

• Reject or drop the data packets that contain SQL statements, shell commands, or script tags in the input data, which can prevent or reduce the injection attacks.
• Reject or drop the data packets that exceed a certain size or length in the input data, which can prevent or reduce the buffer overflow attacks.
• Reject or drop the data packets that contain malformed or invalid syntax or characters in the input data, which can prevent or reduce the DoS attacks.

Adding a new rule to the application layer firewall can be done quickly and easily, without requiring any changes or patches to the web-based system, which can be time-consuming and risky, especially for a critical system. Adding a new rule to the application layer firewall can also be done remotely and centrally, without requiring any physical access or installation on the web-based system, which can be inconvenient and costly, especially for a distributed system.

The other options are not the most suited to quickly implement a control for an input validation and exception handling vulnerability on a critical web-based system, but rather options that have other limitations or drawbacks. Blocking access to the service is not the most suited option, because it can cause disruption and unavailability of the service, which can affect the business operations and customer satisfaction, especially for a critical system. Blocking access to the service can also be a temporary and incomplete solution, as it does not address the root cause of the vulnerability or prevent the attacks from occurring again. Installing an Intrusion Detection System (IDS) is not the most suited option, because IDS only monitors and detects the attacks, and does not prevent or respond to them. IDS can also generate false positives or false negatives, which can affect the accuracy and reliability of the detection. IDS can also be overwhelmed or evaded by the attacks, which can affect the effectiveness and efficiency of the detection. Patching the application source code is not the most suited option, because it can take a long time and require a lot of resources and testing to identify, fix, and deploy the patch, especially for a complex and critical system. Patching the application source code can also introduce new errors or vulnerabilities, which can affect the functionality and security of the system. Patching the application source code can also be difficult or impossible, if the system is proprietary or legacy, which can affect the feasibility and compatibility of the patch.

Link Control Protocol (LCP) is used by the Point-to-Point Protocol (PPP) to determine packet formats. PPP is a data link layer protocol that provides a standard method for transporting network layer packets over point-to-point links, such as serial lines, modems, or dial-up connections. PPP supports various network layer protocols, such as IP, IPX, or AppleTalk, and it can encapsulate them in a common frame format. PPP also provides features such as authentication, compression, error detection, and multilink aggregation. LCP is a subprotocol of PPP that is responsible for establishing, configuring, maintaining, and terminating the point-to-point connection. LCP negotiates and agrees on various options and parameters for the PPP link, such as the maximum transmission unit (MTU), the authentication method, the compression method, the error detection method, and the packet format. LCP uses a series of messages, such as configure-request, configure-ack, configure-nak, configure-reject, terminate-request, terminate-ack, code-reject, protocol-reject, echo-request, echo-reply, and discard-request, to communicate and exchange information between the PPP peers.

The other options are not used by PPP to determine packet formats, but rather for other purposes. Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol that allows the creation of virtual private networks (VPNs) over public networks, such as the Internet. L2TP encapsulates PPP frames in IP datagrams and sends them across the tunnel between two L2TP endpoints. L2TP does not determine the packet format of PPP, but rather uses it as a payload. Challenge Handshake Authentication Protocol (CHAP) is an authentication protocol that is used by PPP to verify the identity of the remote peer before allowing access to the network. CHAP uses a challenge-response mechanism that involves a random number (nonce) and a hash function to prevent replay attacks. CHAP does not determine the packet format of PPP, but rather uses it as a transport. Packet Transfer Protocol (PTP) is not a valid option, as there is no such protocol with this name. There is a Point-to-Point Protocol over Ethernet (PPPoE), which is a protocol that encapsulates PPP frames in Ethernet frames and allows the use of PPP over Ethernet networks. PPPoE does not determine the packet format of PPP, but rather uses it as a payload.

 The purpose of an Internet Protocol (IP) spoofing attack is to convince a system that it is communicating with a known entity. IP spoofing is a technique that involves creating and sending IP packets with a forged source IP address, which is usually the IP address of a trusted or authorized host. IP spoofing can be used for various malicious purposes, such as:

• Bypassing IP-based access control lists (ACLs) or firewalls that filter traffic based on the source IP address.
• Launching denial-of-service (DoS) or distributed denial-of-service (DDoS) attacks by flooding a target system with spoofed packets, or by reflecting or amplifying the traffic from intermediate systems.
• Hijacking or intercepting a TCP session by predicting or guessing the sequence numbers and sending spoofed packets to the legitimate parties.
• Gaining unauthorized access to a system or network by impersonating a trusted or authorized host and exploiting its privileges or credentials.

The purpose of IP spoofing is to convince a system that it is communicating with a known entity, because it allows the attacker to evade detection, avoid responsibility, and exploit trust relationships.

The other options are not the main purposes of IP spoofing, but rather the possible consequences or methods of IP spoofing. To send excessive amounts of data to a process, making it unpredictable is a possible consequence of IP spoofing, as it can cause a DoS or DDoS attack. To intercept network traffic without authorization is a possible method of IP spoofing, as it can be used to hijack or intercept a TCP session. To disguise the destination address from a target’s IP filtering devices is not a valid option, as IP spoofing involves forging the source address, not the destination address.

 Packet filtering operates at the network layer of the Open System Interconnection (OSI) model. The OSI model is a conceptual framework that describes how data is transmitted and processed across different layers of a network. The OSI model consists of seven layers: application, presentation, session, transport, network, data link, and physical. The network layer is the third layer from the bottom of the OSI model, and it is responsible for routing and forwarding data packets between different networks or subnets. The network layer uses logical addresses, such as IP addresses, to identify the source and destination of the data packets, and it uses protocols, such as IP, ICMP, or ARP, to perform the routing and forwarding functions.

Packet filtering is a technique that controls the access to a network or a host by inspecting the incoming and outgoing data packets and applying a set of rules or policies to allow or deny them. Packet filtering can be performed by devices, such as routers, firewalls, or proxies, that operate at the network layer of the OSI model. Packet filtering typically examines the network layer header of the data packets, such as the source and destination IP addresses, the protocol type, or the fragmentation flags, and compares them with the predefined rules or policies. Packet filtering can also examine the transport layer header of the data packets, such as the source and destination port numbers, the TCP flags, or the sequence numbers, and compare them with the rules or policies. Packet filtering can provide a basic level of security and performance for a network or a host, but it also has some limitations, such as the inability to inspect the payload or the content of the data packets, the vulnerability to spoofing or fragmentation attacks, or the complexity and maintenance of the rules or policies.

The other options are not techniques that operate at the network layer of the OSI model, but rather at other layers. Port services filtering is a technique that controls the access to a network or a host by inspecting the transport layer header of the data packets and applying a set of rules or policies to allow or deny them based on the port numbers or the services. Port services filtering operates at the transport layer of the OSI model, which is the fourth layer from the bottom. Content filtering is a technique that controls the access to a network or a host by inspecting the application layer payload or the content of the data packets and applying a set of rules or policies to allow or deny them based on the keywords, URLs, file types, or other criteria. Content filtering operates at the application layer of the OSI model, which is the seventh and the topmost layer. Application access control is a technique that controls the access to a network or a host by inspecting the application layer identity or the credentials of the users or the processes and applying a set of rules or policies to allow or deny them based on the roles, permissions, or other attributes. Application access control operates at the application layer of the OSI model, which is the seventh and the topmost layer.