Hosts are any servers, workstations, or other computing devices and host security refers to methods used to protect them. In an ideal world, hosts start in a secure state. Unfortunately, it’s not an ideal world, and administrators need to be proactive host security before deployment and keep hosts secure after deployment.
This blog outlines several steps used to secure hosts, starting with basic hardening methods. Many organizations use different types of baselines, such as security baselines, configuration baselines, and performance baselines, to assist in the hardening process. Additionally, many organizations use imaging technologies to create standardized images with mandatory security settings.
Note: This blog is an excerpt from the
CompTIA Security+: Get Certified Get Ahead: SY0-301 Study Guide.
Host Security – Hardening Systems
Hardening is the practice of making a system or application more secure from its default installation. This section covers steps to harden the operating system but you should also be aware of steps required to harden applications.
Key steps to harden a server or workstation include:
- Protecting passwords
- Disabling unnecessary services
- Disabling unneeded applications
- Protecting management interfaces and applications
Other blogs have covered the different steps used to protect passwords, including the use of password policies to ensure users follow secure password practices. This blog will explore the other items in this list. Additional hardening steps covered later in this chapter include keeping systems up-to-date with patch management and controlling the configuration with change management controls.
Host Security -Disabling Unnecessary Services
A core principle associated with hardening a system includes removing all unnecessary services. If a service is not running on a system, attackers cannot attack it. For example, an expert on exploiting FTP vulnerabilities will be unsuccessful using these techniques on a server that is not running the FTP service. It doesn’t matter how vulnerable a service is. If it’s not running, it can’t be attacked.
When you disable a service, you often remove access to the associated protocol. For example, if you disable the FTP service, you disable the FTP protocol. Some protocols, such as TCP, UDP, IP, and ARP, are necessary for connectivity within a TCP/IP network. Other protocols, such as HTTP, SMTP, and FTP, are optional application protocols and only run to support the underlying service.
Disabling unnecessary services and removing unneeded protocols provides several key benefits, including the following:
- Provides protection against zero day attacks. A zero day attack is an attack on an undisclosed vulnerability. Some attackers know about the vulnerability, but it is not public knowledge, and the vendor has not released a patch. By limiting the services and protocols running on a system, you limit vulnerabilities against zero day attacks.
- Reduces risks associated with open ports. If an attacker does a port scan, the port scan fails on the associated port fail. For example, disabling the FTP service on a server causes a port scan on ports 20 and 21 to fail even if these ports are open on a firewall.
Disabling unused services is a key step in protecting systems from attacks such as zero day attacks, malware, or risks associated with open ports. This is an important step for both operating system hardening and application hardening.
Host Security – Eliminate Unneeded Applications
In addition to disabling unnecessary services to reduce vulnerabilities, it’s important to uninstall unneeded software. Software frequently has bugs and vulnerabilities. While patching software will frequently close these vulnerabilities, you can eliminate these vulnerabilities by simply eliminating unneeded applications.
Years ago, I was working at a small training company. One of the servers had a default installation of Windows. We were using the server as a file server, but since it wasn’t hardened from the default installation, it was also running Internet Information Services (IIS), Microsoft’s web server.
At some point, attackers released the Nimda virus that exploited a vulnerability with IIS. Microsoft released a patch for IIS, but since IIS was installed by default and we weren’t using it, we also weren’t managing it. Ultimately, the Nimda virus found our server, and the worm component of Nimda quickly infected our network. If the IIS software hadn’t been installed, the server would not have been vulnerable to the attack.
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