Firewalls and Network Defense:-
A system administrator can utilise a variety of appliances available on the market to safeguard the network. These devices operate in various ways and focus on many layers to perform threat detection, attack prevention, and access control.
• Evading firewalls
• Advanced stealth scanning
• Filtering evasion
On a computer or a specific network device, firewalls are specialised software modules.
They function as a network's packet filter for incoming and outgoing data. System administrators and desktop users can manage access to network resources and services with the aid of firewalls. A firewall can operate on many OSI model layers, offering various functions and security measures.
Firewalls:
You must be aware of how firewalls operate and the kind of attacks they shield against. In the slides that follow, you will learn why it is incorrect for individuals to think that firewalls and antivirus software are the only security measures they require.
Packet Filtering Firewalls:
Packet filtering is the firewall's most fundamental function. An administrator can use packet filtering to set rules that will filter packets based on criteria like:
• Source IP address
• Destination IP address
• Protocol
• Source port
• Destination Port
The mainstay of network security is packet filtering, which is supported by both high-end enterprise routers and residential DSL routers.
Each packet's header is examined by packet filters to determine how to handle it. The more frequent behaviours are:
Allowing a packet to pass; Dropping a packet without sending a diagnostic message to the packet source host; and Denying a packet while informing the source host A packet's real content cannot be determined by looking at the header, for instance. Network administrators in a company set up a company firewall to permit web browsing from the internal network. They achieve this by allowing TCP traffic to use destination ports 80 or 443.What happens if a machine inside the network tries to SSH connect to a server that is listening on port 80?
Even if it isn't online traffic, the flow of traffic will continue!
Let's examine a common scenario when packet inspection fails to prevent a hacker from abusing a service. Application Attacks vs. Packet Filtering A business maintains a web server. All incoming Internet traffic will be permitted by the firewall and routed to the web server's port 80.
Application Attacks vs Packet Filtering:-
The firewall cannot tell a web application exploit from normal web browsing, hence application exploits will also pass through.
Only IP addresses, ports, and protocols can be used by the firewall to filter traffic. Any application layer traffic, including hacker exploits, will pass. The many different types of application layer exploits include XSS, buffer overflows, SQL injections, and many others.
Layer 7 assaults cannot be stopped by packet filtering alone. Let's examine a different scenario.
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