A great deal of confusion exists about the role that ISA Server can play in a network environment. Much of that confusion stems from the misconception that ISA Server is only a proxy server. ISA Server 2004 is, on the contrary, a fully functional firewall, VPN, web caching proxy, and application reverse-proxy solution. In addition, ISA Server 2004 addresses specific business needs to provide a secured infrastructure and improve productivity through the proper application of its built-in functionality. Determining how these features can help to improve the security and productivity of an organization is subsequently of key importance.
In addition to the built-in functionality available within ISA Server 2004, a whole host of third-party integration solutions provide additional levels of security and functionality. Enhanced Intrusion Detection support, content filtering, web surfing restriction tools, and customized application filters all extend the capabilities of ISA Server and position it as a solution to a wide variety of security needs within organizations of many sizes.
Outlining the High Cost of Security Breaches
It is rare that a week goes by without a high-profile security breach, denial-of-service (DoS) attack, exploit, virus, or worm appearing in the news. The risks inherent in modern computing have been increasing exponentially, and effective counter-measures are required in any organization that expects to do business across the Internet.
It has become impossible to turn a blind eye toward these security threats. On the contrary, even organizations that would normally not be obvious candidates for attack from the Internet must secure their services because the vast majority of modern attacks do not focus on any one particular target, but sweep the Internet for any destination host, looking for vulnerabilities to exploit. Infection or exploitation of critical business infrastructure can be extremely costly for an organization. Many of the recent productivity gains in business have been attributed to advances in Information Technology functionality, and the loss of this functionality can severely impact the bottom line.
In addition to productivity losses, the legal environment for businesses has changed significantly in recent years. Regulations such as Sarbanes Oxley (SOX), HIPAA, and Gramm Leach Blilely have changed the playing field by requiring a certain level of security and validation of private customer data. Organizations can now be sued or fined for substantial sums if proper security precautions are not taken to protect client data. The atmosphere surrounding these concerns provides the backdrop for the evolution and acceptance of the ISA Server 2004 product.
Outlining the Critical Role of Firewall Technology in a Modern Connected Infrastructure
It is widely understood today that valuable corporate assets cannot be exposed to direct access to the world's users on the Internet. In the beginning, however, the Internet was built on the concept that all connected networks could be trusted. It was not originally designed to provide robust security between networks, so security concepts needed to be developed to secure access between entities on the Internet. Special devices known as firewalls were created to block access to internal network resources for specific companies.
Originally, many organizations were not directly connected to the Internet. Often, even when a connection was created, there was no type of firewall put into place because the perception was that only government or high-security organizations required protection.
With the explosion of viruses, hacking attempts, and worms that began to proliferate, organizations soon began to understand that some type of firewall solution was required to block access to specific "dangerous" TCP or UDP ports that were used by the Internet's TCP/IP protocol. This type of firewall technology would inspect each arriving packet and accept or reject it based on the TCP or UDP port specified in the packet of information received.
Some of these firewalls were ASIC-based firewalls, which employed the use of solid-state microchips, with built-in packet filtering technology. These firewalls, many of which are still used and deployed today, provided organizations with a quick and dirty way to filter Internet traffic, but did not allow for a high degree of customization because of their static nature.
The development of software-based firewalls coincided with the need for simpler management interfaces and the capability to make software changes to firewalls quickly and easily. The most popular firewall in organizations today, CheckPoint, falls into this category, as do other popular firewalls such as SonicWall and Cisco PIX. ISA Server 2004 was built and developed as a software-based firewall, and provides the same degree of packet-filtering technology that has become a virtual necessity on the Internet today.
More recently, holes in the capabilities of simple packet-based filtering technology have made a more sophisticated approach to filtering traffic for malicious or spurious content a necessity. ISA Server 2004 responds to these needs with the capabilities to perform application-layer filtering on Internet traffic.
Understanding the Growing Need for Application-Layer Filtering
Nearly all organizations with a presence on the Internet have put some type of packet filtering firewall technology into place to protect the internal network resources from attack. These types of packet-filter firewall technologies were useful in blocking specific types of network traffic, such as vulnerabilities that utilize the RPC protocol, by simply blocking TCP and UDP ports that the RPC protocol would use. Other ports, on the other hand, were often left wide open to support certain functionality, such as the TCP 80 port, utilized for HTTP web browsing. As previously mentioned, a packet filter firewall is able to inspect only the header of a packet, understanding which port the data is meant to utilize, but unable to actually read the content. A good analogy to this would be if a border guard was instructed to allow only citizens with specific passports to enter the country, but had no way of inspecting their luggage for contraband or illegal substances.
The problem that is becoming more evident, however, is that the viruses, exploits, and attacks have adjusted to conform to this new landscape, and have started to realize that they can conceal the true malicious nature of their payload within the identity of an allowed port. For example, they can piggy-back their destructive payload over a "known good" port that is open on a packet-filter firewall. Many modern exploits, viruses, and "scumware," such as illegal file sharing applications, piggy-back off the TCP 80 HTTP port, for example. Using the border guard analogy to illustrate, the smugglers realized that if they put their contraband in the luggage of a citizen from a country on the border guard's allowed list, they could smuggle it into the country without worrying that the guard would inspect the package. These types of exploits and attacks are not uncommon, and the list of known application-level attacks continues to grow.
In the past, when an organization realized that it had been compromised through its traditional packet filter firewall, the common knee-jerk reaction was to lock down access from the Internet in response to threats. For example, an exploit that would arrive over HTTP port 80 might prompt an organization to completely close access to that port for a temporary or semi-permanent basis. This approach can greatly impact productivity, especially in a modern connected infrastructure that relies heavily on communications and collaboration with outside vendors and customers. Traditional security techniques involved a trade-off between security and productivity. The tighter a firewall was locked down, for example, the less functional and productive an end-user could be.
In direct response to the need to maintain and increase levels of productivity without compromising security, application-layer "stateful inspection" capabilities were built into ISA Server that could intelligently determine whether particular web traffic were legitimate. To illustrate, ISA Server inspects a TCP packet traveling across Port 80 to determine whether it is a properly formatted HTTP request. Looking back to the smuggling analogy, ISA Server is like a border guard who not only checks the passports, but is also given an X-ray machine to check the luggage of each person crossing the border.
The more sophisticated application-layer attacks become, the greater the need becomes for a security solution that can allow for a greater degree of productivity while reducing the types of risks that can exist in an environment that relies on simple packet-based filtering techniques.
For more information on the specifics of working with and setting up application-based filtering technology to secure inbound traffic and control access to internal resources, refer to Part III of this book, "Securing Servers and Services with ISA Server 2004."